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COUNTRY  LIFE  EDUCATION 
SERIES 


Edited  by  Charles  William  Burkett,  recently  Director 

of  Experiment  Station,  Kansas  State  Agricultural 

College ;  Editor  of  American  Agriculturist 


TTPES  AND  BREEDS  OF  FARM  ANIMALS 
By  Charles  S.  Plumb,  Ohio  State  University 

PRINCIPLES  OF  BREEDING 

By  Eugene  Davenport,  University  of  Illinois 

FUNGOUS  DISEASES  OF  PLANTS 

By  Benjamin  Minge  Duggar,  Cornell  University 

SOIL  FERTILITY  AND  PERMANENT 
AGRICULTURE 

By  Cyril  G.  Hopkins,  University  of  Illinois 

Other  volumes  in  preparation 


PRINCIPLES  OF  BREEDING 


A  TREATISE  ON  THREMMATOLOGY 

OR 

THE  PRINCIPLES  AND  PRACTICES  INVOLVED  IN  THE 
ECONOMIC  IMPROVEMENT  OF  DOMESTI- 
CATED ANIMALS  AND  PLANTS 


BY 


E.  DAVENPORT,  M.AGR,  LL.D. 

PROFESSOR  OF  THREMMATOLOGY  IN  THE  UNIVERSITY  OF  ILLINOIS 

DEAN  OF  THE  COLLEGE  OF  AGRICULTURE 
DIRECTOR  OF  THE  AGRICULTURAL  EXPERIMENT  STATION 


WITH  APPENDIX 

BY 

H.  L.  RIETZ,  PH.D. 

ASSISTANT  PROFESSOR  OF  MATHEMATICS  IN  THE  UNIVERSITY  OF  ILLINOIS 


GIN-N.&  COMPANY 

BOSTON  .  NEW  YORK  •  CHICAGO  •  LONDON 


ENTERED  AT  STATIONERS'  HALL 


COPYRIGHT,  1907 
BY  EUGENE  DAVENPORT 


ALL    RIGHTS    RESERVED 


710.10 


GINN  &  COMPANY  .  PRO- 
PRIETORS  •  BOSTON  •  U.S.A. 


PREFACE 

Two  classes  of  people  have  been  in  mind  in  the  preparation  of 
this  text,  viz.  the  student  of  agriculture  in  the  college  and  experi- 
ment station  and  the  practical  breeder  upon  the  farm.  Both  need 
to  know  all  that  evolution  has  to  teach  of  methods  that  may  be 
employed  in  still  further  adapting  to  our  needs  such  animals  and 
plants  as  have  been  domesticated  because  of  their  valuable  natural 
qualities. 

The  general  purpose  has  been  first  of  all  to  define  the  problems 
involved  in  animal  and  plant  improvement ;  to  free  the  subject 
from  the  prejudice  and  tradition  that  have  always  befogged  it ; 
to  bring  to  the  study  whatever  facts  are  fully  known  to  biological 
science ;  to  recognize  and  define  somewhat  clearly  the  present 
limitations  of  knowledge,  and  to  indicate  as  well  as  may  be  the 
directions  from  which  further  and  much-needed  light  is  most 
likely  to  come.  Last  of  all  and  more  than  all,  it  has  been  the 
purpose  to  encourage,  and  if  possible  induce,  more  exact  methods 
of  study  and  of  practice  than  have  hitherto  characterized  this 
branch  of  agricultural  science. 

It  is  yet  too  early  to  prepare  an  ideal  treatise  upon  this  most 
intricate  subject,  and  no  one  is  more  conscious  than  the  author 
of  the  many  deficiencies  and  shortcomings  of  this  attempt.  Some 
effort,  however,  is  surely  needed  at  this  time  to  clear  the  atmos- 
phere, to  give  the  student_pf  agrjtffll|  at  least  a  rational  point 
of  view,  and  to  bring  M^Bito  wBHKship  with  those  who  are 
earnestly  studying  biol^^Bl  problems  and  through  whose  efforts 
these  vexed  questions  ^^^ure  sooner  or  later  to  find  a  solution. 
This,  together  with  the^ressing  need  of  a  text  in  his  own  class 
room,  is  the  author's  only  warrant  for  the  present  volume. 

No  new  theories  of  evolution  are  proposed.  The  chief  object 
has  been  to  distinguish  what  is  known  from  what  is  merely  tradi- 
tional ;  to  give  as  much  as  possible,  within  the  limits  of  available 
space,  of  the  best  established  facts  bearing  upon  this  subject ;  to 


vi  PREFACE 

call  attention  to  approved  methods  of  study,  and  to  indicate  lines 
of  research  most  likely  to  furnish  valuable  information  in  the  not 

distant  future. 

It  is  necessary  to  introduce  a  considerable  amount  of  mathe- 
matical work  in  the  later  chapters.  No  excuse  is  offered  for  this 
introduction,  and  it  is  earnestly  desired  that  the  reader  give 
special  attention  to  this  portion  of  the  text,  whether  easy  or  diffi- 
cult of  following,  because  it  is  by  this  road  that  many  new  princi- 
ples will  arrive  and  that  many  of  our  future  operations  must  be 
ordered ;  for  nothing  is  clearer  than  that  the  successful  breeder 
of  the  future  will  be  a  bookkeeper  and  a  statistician.  For  the 
convenience  of  the  non-mathematical  reader  general  formulae  are 
placed  in  footnotes,  and  some  of  the  more  abstract  matter  is 
placed  in  the  form  of  an  appendix  for  the  benefit  of  the  more 
mathematically  inclined. 

The  writer  has  taught  this  subject  for  fifteen  years  and  is  fully 
aware  of  the  pedagogic  difficulties  involved  as  well  as  of  the 
limitations  of  knowledge.  He  has  tried  many  different  outlines 
and  many  different  methods  of  presentation,  and  has  chosen  the 
one  here  employed  because  in  experience  it  seems  the  most 
favorable  for  the  presentation  of  the  subject-matter  involved  and 
at  the  same  time  for  putting  the  student  in  a  frame  of  mind 
favorable  for  the  undertaking  of  economic  breeding  operations 
and  for  the  reception  of  new  truths  as  they  shall  be  discovered. 

Variation  rather  than  heredity  has  been  chosen  for  the  initial 
and  leading  thought  because  better  calculated,  as  experience  has 
shown,  to  afford  a  favorable  outlook  and  to  develop  such  con- 
ceptions of  evolution  as  ^Mnost  useful  later  on. 

The  evolutionist  who  I  H^ancjfe^can  these  pages  would 
be  struck  by  the  absence  orsomeB  Be  cardinal  features  of 
evolution,  as  he  would  also  note  the  S  feing  prominence  given 
to  certain  other  questions  of  seeming  n^^r  importance.  Herein 
exists  the  difference  between  thremmatology  and  evolution,  and 
this  very  matter  has  given  the  author  more  difficulty  than  all 
others,  viz.  to  rearrange  values  and  to  determine  proper  relations 
of  old  questions  in  a  new  field. 

We  must  discuss  the  causes  of  variation  even  though  we  are 
told  by  the  best  students  that  such  attempts  are  premature.  A 


PREFACE  vii 

minor  matter  in  evolution,  curious  rather  than  otherwise,  it  is  a 
vital  one  in  thremmatology,  and  we  must  discuss  the  subject  the 
best  we  are  able,  if  only  to  learn  how  little  we  really  know  about 
it  and  to  point  attention  in  the  right  direction. 

No  attempt  has  been  made  to  include  exhaustive  references. 
On  the  other  hand,  they  are  confined  for  the  most  part  to  a  few 
standard  books  easy  of  access,  and  to  save  time  the  references 
are  mostly  to  definite  pages.  A  general  and  more  extended  list 
follows  the  summary  of  nearly  every  chapter,  enabling  the  student 
to  pursue  that  particular  subject  further  if  desired  ;  but  there  is 
no  attempt  at  a  complete  bibliography.  It  was  hoped  that  if  the 
list  of  references  could  be  kept  small  the  student  and  the  breeder 
would  be  the  more  likely  to  provide  themselves  with  standard 
literature  bearing  on  the  subject.  I  have  made  the  freest  use  of 
standard  authors,  giving  full  credit  in  all  cases,  generally  in  the 
form  of  reference  to  text  and  page.  This  course  has  been  dictated 
by  the  desire  to  furnish  the  student  with  reliable  facts  rather 
than  a  series  of  academic  discussions  upon  disputed  subjects. 

I  desire  to  acknowledge  the  very  great  services  of  Dr.  Rietz, 
to  whom  I  am  indebted  for  much  assistance  in  the  more  statistical 
portions,  and  for  the  preparation  of  the  appendix  especially 
directed  to  the  mathematical  student,  not  as  a  text  but  as  an 
introduction  to  further  study  in  this  special  phase  of  science. 

I  am  also  indebted  to  many  of  my  colaborers  in  the  Univer- 
sity of  Illinois  and  elsewhere,  as  well  as  to  numerous  breeders  in 
this  and  other  states,  who  by  their  assistance  have  contributed 
much  to  any  success  which  this  volume  may  meet. 

Its  possible  merits,  therefore,  I^^sJ  share  with  others ;  its 
defects  and  shortcominsMre  &^4l 

^BB  E.  DAVENPORT 


UNIVERSITY  OF  ILLINO 
URBANA 


.nijj^^n 

W 


CONTENTS 

PAGE 
INTRODUCTION i 

PART  I  — VARIATION 

CHAPTER 

I.   VARIATION  IN  GENERAL 7 

I.  Variation  Universal  among  Living  Beings  ....       7 

II.  Variability  the  Basis  for  Improvement 9 

III.  Nature  of  Variability 10 

IV.  Meaning  of  the  Term  "  Character  " 11 

V.  Dominant  and  Latent  Characters .13 

VI.  The  Unit  of  Variability        .         . 15 

VII.  Distinctions  as  to  Kinds  of  Variations         .         .         .         .         .     17 
References    .         .         .         .         .         .         .  .         .         .24 

II.   MORPHOLOGICAL  VARIATION .        .25 

References 29 

III.  SUBSTANTIVE  VARIATION 30 

IV.  MERISTIC  VARIATION 33 

I.  Symmetry 34 

II.  Meristic  Variation  in  Linear  Series 39 

III.  Meristic  Variation  and  Bilateral  Symmetry  .         .         .         -65 

IV.  Symmetry  in  Variable  Parts         :         .         .         .         .         .         .68 

V.  Meristic  Variation  in  Radial  Series 70 

VI.  Importance  of  Meristic  Variation         .         .         .         .         .         -73 
References 74 

V.  FUNCTIONAL  VARIATION 75 

I.  Variation  in  the   Degree  of  Activity  of  Normal  Functions  be- 
tween Different  Individuals  of  the  Same  Species    .         .         -77 
II.  Variation  in  the  Degree  of  Activity  of  Normal  Functions  within 

the  Same  IndTvidual 91 

III.  Modification  of  Normal  Functions  by  External  or  Other  Influ- 

ences        .         .         .         .         .     • 98 

IV.  Normal  Functions  exercised  under  Abnormal  Conditions  .         .107 

References        .:        .         .         .         .         .         .         .         .         .   109 

VI.  MUTATIONS    .         .        . no 

I.  Distinction  between  Mutation  and  Ordinary  Variation        .         .no 

II.  Examples  of  Mutation .   in 


X  CONTENTS 

CHAPTER  PAGE 

III.  Experiments  of  De  Vries .114 

IV.  American  Experiences 129 

V.  Economic  Significance  of  Mutations          .        .        .        .    .     .     135 

VI.  Biological  Significance  of  Mutations 136 

References      • .     139 

PART  II  — CAUSES  OF  VARIATION 

INTRODUCTION .        .141 

VII.   THE  MECHANISM  OF  DEVELOPMENT  AND  DIFFERENTIATION         .     142 

I.  Protoplasm  the  Physical  Basis  of  Life       .         .         .    u'     .     142 

II.  The  Cell  the  Unit  of  Structure          .         .  .         .         .143 

III.  Mechanism  of  Cell  Division  (Mitosis) 145 

IV.  Cell  Division  with  and  without  Differentiation          .         .  149 
V.  Physiological  Units            . 152 

References ,         -154 

VIII.    INTERNAL  CAUSES  OF  VARIATION 155 

/.   INTERNAL    INFLUENCES   AFFECTING  PRIMARILY  THE  IN- 
DIVIDUAL    155 

I.  Cell  Division 155 

II.  Bisexual  Reproduction  a  Fundamental  Cause  of  Variation       .  160 

III.  Maturation  and  the  Reduction  of  the  Chromosomes  a  Cause 

of  Variation  163 

IV.  Bud  Variation 181 

V.  Influence  of  the  Condition  of  the  Germ  upon  Development      .     182 

VI.  Xenia,  or  Fertilization  of  the  Endosperm          .         .         .         .183 
VII.  Telegony 185 

VIII.  Intra-Uterine  Influences    .         . 189 

IX.  Reversion  and  Atavism .192 

X.  Individual  Characters  dependent  upon  Sex       .         .         .         .194 
II.  INTERNAL    INFLUENCES    AFFECTING     THE    RACE    AS    A 

WHOLE      . 196 

XI.  Relative  Fertility,  or  Genetic  Selection 196 

XII.  Physiological  Selection .201 

XIII.  Selective  Death  Rate ;  Longevity 201 

XIV.  Bathmic  Influences 202 

XV.  Physiological  Units 208 

XVI.  Germinal  Selection 213 

References * 217 

IX.   EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION        .        .        .  220 
I.  General  Effect  of  Locality  upon  Plant  and  Animal  Develop- 
ment   221 

II.  Influence  of  Food  upon  Variability  .....  225 

III.  Effect  of  Moisture  upon  Development 230 

IV.  Effect  of  Contact  upon  Protoplasmic  Activity  ....  233 
V.  Effect  of  Gravity  upon  Living  Matter  ;  Geotropism          .         .  236 

VI.  Effect  of  Light  upon  Living  Matter 239 


CONTENTS  xi 

CHAPTER  PAGE 

VII.  Influence  of  Temperature  upon  Living  Matter           .         .         .  254 

VIII.  Effect  of  Chemical  Agents  upon  Protoplasmic  Activity     .         .  264 
IX.  Effect  of    Saline    Solution    upon   Development   in    Aquatic 

Animals .  282 

X.  Influence  of  Use  and  Disuse  upon  Development       .        .        .  285 

XI.  External  Influences  as  Causes  of  Variation  in  Type           .         .  290 

References .  294 

X.  RELATIVE  STABILITY  AND  INSTABILITY  OF  LIVING  MATTER  ,        .  295 

I.  Evidence  from  Stability  of  Type 296 

II.  Evidence  from  Mutability  of  Species           ...         .  298 
ITI.  Evidence  from  Reversion  and  Atavism 305 

IV.  Evidence  from  Disappearance  of  Parts       .         ...         .  306 

V.  Evidence  from  the  Direct  Action  of  the  Environment        .         .  307 

VI.  Evidence  from  Acclimatization           .         .         .         .         .         .  308 

VII.  Evidence  from  Regeneration 316 

VIII.  Internal  Factors  in  Regeneration 332 

IX.  Evidence  from  Grafting      .         .         .- 335 

X.  Evidence  from  the  Origin  of  New  Cells  and  Tissues          .         -336 

XI.  Evidence  from  Development  and  Differentiation        .         .         .  338 

References .  345 

PART  III  — TRANSMISSION 

XI.  TRANSMISSION  OF  MODIFICATIONS  DUE  TO  EXTERNAL  INFLUENCES  348 

I.  Introductory 348 

II.  P>idence  from  the  Nature  of  Variation      .         .                  .         .  356 

III.  Evidence  from  Mutilations          .         .         .         .         .'.'*'.         .  364 

IV.  Evidence  from  Food  Supply 370 

V.  Evidence  from  Acclimatization 374 

VI.  Evidence  from  Habit  and  Instinct 386 

VII.  Evidence  from  Use  and  Disuse 404 

VIII.  Evidence  from  Disappearing  Organs           .....  409 
IX.  Variations    due   to   Causes   not    affecting   the    Germ  are   not 

Transmitted .         .  416 

References .         .         .  418 

XII.   TYPE  AND  VARIABILITY 419 

I.  Type 420 

II.  Variability,  or  Deviation  from  Type 425 

III.  Practical  Hints  on  the  Taking  and  Grouping  of  Measurements  435 

IV.  Probable  Error 437 

V.  Comparative  Type  and  Variability  for  Different  Characters  in 

the  Same  Population .         .  444 

VI.  Effect  of  Selection  upon  Type  and  Variability           .         .         .  445 

VII.  Indirect  Effects  of  Selection  upon  Type  and  Variability    .         .  447 
VIII.  Studies  in  Type  and  Variability  of  the  Same  Variety  of  Corn 

raised  under  Different  Conditions  as  to  Fertility    .         .         .  449 

References 452 


xii  CONTENTS 

CHAPTER  PACK 

XIII.   CORRELATION      .        *        . -453 

I.  Meaning  of  Correlation 453 

II.  Calculation  of  Coefficients  of  Correlation      .         .         .         .  455 

III.  The  Correlation  Table 458 

IV.  The  Correlation  Coefficient 459 

V.  The  Regression  Coefficient 466 

VI.  Studies  in  Speed  Records  6f  Trotters    .         .         .         .         .468 

References 472 

XIV.   HEREDITY  .".".' 473 

I.  How  Characters  behave  in  Transmission        ....  473 

II.  Statistical  Methods  of  Study  of  Heredity      ....  478 

III.  The  Regression  Table 479 

IV.  Like  Parents  beget  Unlike  Offspring  and,  conversely,  Like 

Offspring  may  be  begotten  by  Unlike  Parents    .         .         .  482 
V.  Regression.    In   general,  the    Offspring  is   More   Mediocre 
than  the  Parents;  that  is,  Whatever  the  Parentage,  the 
Offspring  exhibits  a  Strong  Tendency  to  regress  toward  the 

Mean  of  the  Race 484 

VI.  The  Measure  of  Heredity       .         .         .         .         .         .         .486 

VII.  The  Mean  of  the  Offspring  not  necessarily  the  Same  as  the 

Mean  of  the  Parentage        .......  490 

VIII.  Extremes   of  a  Race   relatively  Less   Productive    than    the 

Means 491 

IX.  Progression.    Parents  in  general  produce  a  Few  Individuals 

More  Extreme  than  the  Race 492 

X.  The   Exceptional    Individual  arises  either  from   Mediocrity 

or  from  the  Exceptional  Parent 499 

XI.  Fraternal   Variability,  —  Offspring    of    Same    Parents    not 

Identical      ...                500 

XII.  Characters    tend    to    combine    in    Definite    Mathematical 

Proportions 504 

XIII.  Mendel's  Law  of  Hybrids 513 

XIV.  The  Law  of  Ancestral  Heredity 525 

XV.  Limit  to  the  Reduction  of  Variability    .....  534 

XVI.  Power  of  Selection  to  permanently  modify  Types  by  the 

Establishment  of  Breeds 537 

XVII.  Breeding  True,  or  Stability  of  a  Character  established  by 

Selection 541 

XVIII.  Duration  of  Varieties,  Breeds,  and  Family  Strains          .         .  544 

References 547 

XV.   PREPOTENCY 551 

I.  Data  from  the  Trotting  Records  illustrating  Prepotency        .  551 

II.  Prepotency  in  Sex  .........  567 

III.  Influence  of  Age  on  Prepotency     ......  573 

IV.  Influence  of  Constitutional  Vigor  upon  Prepotency       .         .  573 
References       .                           <. 575 


CONTENTS  xiii 

PART    IV— PRACTICAL  PROBLEMS 

CHAPTER  PAGE 

XVI.   SELECTION 577 

I.  Ideals  in  Selection 578 

II.  Historical  Knowledge  of  the  Breed  Necessary      .         .         .  579 

III.  General  Principles  involved  in  Selection        ....  581 

IV.  Rational  Selection          .         . 592 

XVII.    SYSTEMS  OF  BREEDING 599 

I.  Purposes  in  Breeding 599 

II.  Grading 602 

III.  Crossing  or  Hybridizing 608 

IV.  Line  Breeding         . 610 

V.  Inbreeding .  613 

VI.  Breeding  from  the  Best 626 

References 628 

XVIII.   THE  DETERMINATION  OF  SEX 629 

I.  Theories 629 

II.  Influence  of  Nutrition    .         .         .         .         ,         .         .         .631 

III.  Influence  of  Fertilization 632 

IV.  Sex  in  Mammals 634 

V.  The  Accessory  Chromosome  and  Sex  Determination    .         .  634 

References 637 

XIX.   PLANT  BREEDING 639 

I.  Advantages  and  Limitations 639 

II.  Soil  and  Culture  Conditions 641 

III.  Systems  of  Planting 643 

References 651 

XX.   ANIMAL  BREEDING          .        .        . 654 

I.  Advantages  and  Disadvantages 654 

II.  Fewer  Characters  for  Selection 656 

III.  Fashion .658 

IV.  Show-Ring  Consequences 660 

V.  Testing  of  Sires  and  Dams 660 

VI.  Weathering  a  Period  of  Depression  and  Preserving  the  Herd  665 

VII.  Records 666 

VIII.  Disposal  of  Surplus  Females          .         .         .         .         .         .  672 

IX.  A  Market  for  Sires 673 

X.  Community  Breeding 674 

XI.  The  Young  Breeder 675 

References 676 

XXI.   DEVELOPMENT 677 

APPENDIX .        .  681 

INDEX                                                                                                                  .  71S 


THE    PRINCIPLES   OF   BREEDING 
THREMMATOLOGY 

INTRODUCTION 

The  main  title  of  the  present  volume  was  chosen  because  self- 
explanatory,  though  it  less  accurately  expresses  the  scope  of  the 
subject  than  does  the  sub-title,  which  is  only  beginning  to  come 
into  general  use. 

Thremmatology,  from  the  Greek  thremma,  a  thing  bred,  is  a 
term  proposed  by  Ray  Lancaster1  to  cover  the  principles  and 
practices  concerned  in  the  improvement  of  domesticated  animals 
and  plants. 

The  term  is  broader  than  the  "  principles  of  breeding  "  because 
it  includes  development  as  well  as  reproduction.  It  is  distinct 
from  evolution  in  general,  which  attempts  to  explain  the  princi- 
ples and  forces  connected  with  the  origin  and  development  of  all 
forms  of  life  but  without  the  slightest  reference  to  economic 
considerations.  In  evolution  a  protozoon  is  as  important  as  a 
pig,  a  hydra  of  as  much  significance  as  a  horse,  and  the  most 
pestiferous  weed  as  much  an  object  of  interest  as  either  corn 
or  wheat. 

Thremmatology  limits  itself  to  those  species  and  varieties  whose 
natural  qualities  made  them  useful  to  man  in  the  beginning,  and 
it  asks  and  seeks  to  answer  this  one  question,  How  can  they  be 
made  still  more  useful  and  better  adapted  to  the  purposes  of  an 
advancing  civilization  ?  In  this  study  forms  of  life  that  are  of  no 
economic  value  are  of  no  special  concern  except  as  their  consider- 
ation may  throw  light  upon  domesticated  forms.  This  latter  is 
often  the  case,  for  it  is  doubtless  true  that  the  same  principles 
apply  to  all  species,  economic  or  otherwise,  because  none  were 

1'See  Encyclopedia  Britannica,  ninth  edition,  XXIV,  841. 


:  /.  ••  INTRODUCTION 
*  *»*       * 

specially  created  for  man  any  more  than  for  any  other  animal. 
It  is  a  general  biological  truth  that  everything  lives  unto  itself, 
—  not  where  it  choses  but  where  it  can  ;  not  upon  what  it  likes 
best  but  upon  what  it  can  get. 

It  may  seem  to  the  student  that  an  undue  amount  of  attention 
is  given  to  variation  and  that  a  disproportionate  amount  of  space  is 
devoted  to  that  subject.  In  that  event  I  have  to  say  that  variation 
is  not  the  antithesis  of  heredity  but  rather  its  constant  and  insep- 
arable attendant,  and  that  the  facts  of  variation  constitute  the 
best  portion  of  that  stock  of  information  with  which  the  student 
must  become  possessed  before  he  is  ready  to  study  the  principles 
involved  in  those  generalizations  upon  which  practical  operations 
may  be  safely  based. 

One  is  painfully  aware,  too,  of  the  necessity  of  ranging  far  and 
wide  for  facts,  and  the  student  cannot  fail  to  feel  ofttimes  that 
the  subject-matter  in  hand  is  far  removed  from  agriculture.  When 
this  is  the  case  it  is  because  we  are  forced  to  take  what  is  avail- 
able and  make  the  most  of  it.  Unfortunately  the  workers  in 
strictly  agricultural  fields  are  all  too  few  and  the  reliable  data 
deplorably  meager,  though  some  original  and  I  trust  valuable 
matter  has  been  recently  added  to  our  stock  of  knowledge. 

While  the  same  principles  doubtless  apply  in  thremmatology 
as  in  evolution,  yet  important  distinctions  are  to  be  observed. 
First,  there  is  every  reason  to  suppose  that  even  fundamental 
laws  apply  to  different  species  in  different  ways.  For  example, 
Indian  corn  seems  particularly  sensitive  to  close  breeding,  whereas 
wheat  is  almost  exclusively  inbred  and  has  been  so  inbred  for 
unknown  generations.  Again,  the  circumstances  of  the  case 
often  introduce  into  the  problem  certain  economic  considerations 
not  resting  upon  general  evolution.  For  example,  man  cannot 
afford  the  "countless  ages  "  and  "  untold  generations  "  which  are 
accorded  nature  for  accomplishing  results.  In  practical  breeding 
operations  substantial  results  must  follow  at  once  and  exhibit  a 
high  degree  of  success  within  the  period  of  a  lifetime  or  they  will 
be  discarded  as  valueless. 

Experience  shows  that  the  purposes,  standards,  and  methods 
of  a  successful  breeder  are  seldom  handed  down  from  one  man 
to  another,  even  to  his  own  son.  Even  if  that  could  be  done,  it 


INTRODUCTION  3 

would  constitute  no  exception  to  the  rule  that  a  man  must  real- 
ize the  fruit  of  his  own  labors  and  in  his  own  generation,  for 
breeding  is  a  business  and  must  be  made  to  pay.  The  breeder 
must  therefore  work  faster  than  nature,  and  thremmatology  can- 
not make  use  of  a  leisurely  operating  evolutionary  principle  unless 
its  action  can  be  accelerated  or  its  cumulative  effects  exaggerated. 
Yet  again,  man  cannot  afford  the  immense  numbers  and  the  whole- 
sale destruction  that  characterize  nature's  methods  of  working 
changes.  Animals  and  even  plants  cost  money,  and  a  relatively 
large  proportion  must  meet  the  conditions,  or  the  enterprise  must 
be  abandoned. 

Business  considerations  therefore  set  arduous  limitations  upon 
thremmatology  in  respect  to  both  time  and  numbers  from  which 
evolution  in  general  is  entirely  free.  The  breeding  business  has 
its  own  particular  problems,  some  of  the  most  important  of  which 
unfortunately  the  known  facts  of  evolution  are  least  able  to 
answer.  The  profitable  study  of  this  subject  will,  however,  be 
assisted  by  a  clear  statement  of  these  problems. 

The  problems  of  the  breeder.  Certain  questions  stand  clearly 
out  in  the  minds  of  practical  breeders,  and  though  an  attempt 
to  answer  them  seriatim  would  not  be  the  best  method  of  study, 
and  though  some  of  them  cannot  be  answered  with  certainty 
in  the  present  state  of  knowledge,  yet  nothing  is  of  more  con- 
sequence at  the  outset  than  that  the  student  get  a  clear  idea  of 
the  problems  needing  solution  and  towards  whose  solution  the 
study  of  thremmatology  is  directed.  They  are  substantially  as 
follows : 

To  what  extent  are  the  characteristics  of  an  individual  at  matur- 
ity due  to  its  ancestry  (heredity),  and  to  what  extent  are  they 
due  to  the  conditions  of  life  (environment),  such  as  food,  climate, 
exercise,  and  general  care  during  development  ? 

Are  the  influences  of  the  conditions  of  life  limited  to  the  indi- 
vidual or  are  they  in  certain  instances  and  to  some  extent  carried 
over  upon  the  offspring  ?  that  is,  are  the  effects  of  environment 
inherited  ? 

Can  variations  be  directly  controlled  to  any  extent  whatever, 
or  only  indirectly  through  selection  and  by  special  care  during 
development  ? 


4  INTRODUCTION 

How  effective  is  selection  in  controlling  variation  ?  that  is,  are 
congenital  variations  due  entirely  to  parentage  or  are  there  back 
of  the  parentage  certain  inherent  and  constitutional  tendencies 
that  largely  fix  the  general  direction  of  variations,  independent 
of  selection  ? 

Does  improvement  consist  in  raising  the  standard  absolutely  or 
only  in  raising  the  general  average  by  eliminating  the  less  desir- 
able ?  that  is,  does  breeding  improve  upon  the  best  or  does  it 
only  bring  the  general  mass  nearer  to  the  upper  level  ? 

To  what  extent  is  evolution  a  gradual  process  and  to  what 
extent  may  profound  advances  appear  suddenly,  as  in  sports  ? 
and  is  the  one  class  of  improvement  any  more  permanent  or  reli- 
able than  the  other  ? 

Do  all  possible  values  of  a  variable  character  appear  or  are 
certain  values  seldom  or  never  presented  ?  that  is  to  say,  is 
variation  always  continuous  or  is  it  sometimes  discontinuous, 
making  certain  things  impossible  because  the  proper  varia- 
tions or  combinations  do  not  appear  on  which  selection  may 
be  based  ? 

What  variations  are  most  likely  to  appear  in  successive  gener- 
ations of  any  given  breed,  variety,  or  type  ? 

Are  variations  correlated  ?  that  is,  do  they  tend  at  ail  to  move 
together,  suggesting  relations  of  cause  and  effect  ? 

What  are  the  proper  standards  for  selection  ?  How  much  shall 
be  given  to  utility  and  how  much  to  appearance  ? 

To  what  extent  is  individual  excellence  a  safe  guide  to  breed- 
ing powers  ? 

To  what  extent  is  the  offspring  like  the  immediate  parent  and 
to  what  extent  does  it  resemble  more  remote  ancestors  ? 

What  is  the  relative  influence  of  sire  and  dam  with  respect  to 
transmission  of  characters  ? 

To  what  extent  do  the  condition  of  the  male  at  the  time  of 
service  and  the  care  of  the  female  during  pregnancy  influence 
the  offspring  ? 

What  are  the  real  dangers  from  close  breeding,  if  any,  and  are 
they  certain  or  only  probable  ? 

How  can  the  advantages  of  close  or  line  breeding  be  realized 
without  encountering  its  dangers  ? 


INTRODUCTION  5 

Will  a  given  breed,  variety,  or  family  strain  endure  indefi- 
nitely under  proper  conditions  or  will  it  inevitably  "run  out," 
necessitating  a  constant  return  to  foundation  stock  for  new 
combinations  as  the  basis  of  improved  strains  ? 

What  are  the  laws  that  determine  the  sex  of  offspring  ? 

Do  the  same  laws  of  breeding  apply  equally  to  animals  and  to 
plants  and  to  all  species  and  varieties  alike,  or  do  different  species 
operate  under  somewhat  different  laws  ? 

Is  a  given  species,  variety,  or  breed  always  subject  to  the  same 
laws  ?  that  is,  are  identical  variations  always  due  to  the  same 
causes  and  do  given  causes  always  produce  the  same  effects  ? 

How  can  results  be  secured  with  the -least  wastage  either  in 
time  or  numbers  ? 

Upon  the  answers  to  these  questions  will  depend  the  policies 
of  all  breeding  enterprises  and  the  permanent  value  of  particular 
family  strains.  Upon  some  of  these  points  there  exists  much 
specific  and  reliable  information  ;  upon  others,  unfortunately,  the 
evidence  is  yet  scanty  and  uncertain.  At  the  present  rate  of 
progress,  however,  we  will  not  have  long  to  wait  for  much  addi- 
tional knowledge.  In  the  meantime  we  must  make  the  best  use 
possible  of  the  information  and  experience  at  hand. 

These  problems  can  best  be  answered  not  by  directing  atten- 
tion to  each  separately,  because  they  overlap,  but  rather  by  follow- 
ing out  what  are  known  to  be  the  characteristic  lines  of  study  in 
the  subject  as  a  whole.  The  order  pursued  in  this  book  is  the  one 
believed  to  be  most  favorable  both  for  this  purpose  and  for  the 
most  successful  answering  of  these  definite  questions.1 

1  A  fair  knowledge  of  general  evolution  is  presumed  on  the  part  of  the  student 
and  reader.  If  this  is  not  in  his  possession,  he  will  do  well  to  read  at  least 
Darwin's  Origin  of  Species  for  a  broad  though  now  somewhat  old  and  incomplete 
outlook  upon  the  general  field.  If  he  desires  to  go  further  and  enter  the  field  of 
controversy,  he  can  do  so  most  directly  by  reading  Weismann's  Essays  on 
Heredity  and  his  Germ  Plasm,  together  with  Romanes'  Examination  of  Weis- 
mannism  and  his  two  volumes  of  Darwin  and  After  Darwin.  If  this  is  done,  it 
Would  be  well  to  finish  with  Habit  and  Instinct  by  Morgan. 


PART   I- -VARIATION 

CHAPTER   I 

VARIATION  IN  GENERAL 

SECTION  I  — VARIATION  UNIVERSAL  AMONG  LIVING 

BEINGS 

The  most  obvious  fact  about  living  beings  is  their  variability. 
Not  only  do  species  differ  from  each  other  by  many  and  widely 
different  characters,  but  individuals  within  the  species  are  distin- 
guished by  differences  readily  discernible,  at  least  by  the  trained 
observer.  The  general  differences  between  horses  and  cattle,  for 
example,  are  specific  and  distinct  and  therefore  striking  even  to 
the  casual  observer ;  but  to  the  trained  eye  all  horses  are  not 
alike,  and  so  it  is  that  differences  are  detected  within  the  species. 
Two  individuals  may  be  recognized  as  possessing  the  same  char- 
acters and  therefore  related  by  descent,  but  invariably  these 
characters  differ  in  degree  or  in  their  proportions  one  to  another. 

Two  animals  may  be  of  the  same  or  of  different  colors,  but  in 
either  event  the  parts  are  differently  proportioned.  The  leg  of 
one  is  longer,  larger,  or  more  crooked  than  that  of  the  other. 
The  bones  composing  the  two  are  not  of  equal,  or  even  of  pro- 
portional, lengths.  Two  cows  of  the  same  breed  differ  marvel- 
ously  in  the  amount  of  milk  they  can  yield  in  a  year,  and  some 
are  known  to  produce  three  times  as  much  butter  fat  as  others 
from  the  same  amount  of  the  same  kind  of  feed.1  Again,  some 
milk  is  rich  in  fat  (6  or  even  8  per  cent)  while  other  is  poor 
(2  per  cent  or  even  less).  Some  horses,  because  of  their  con- 
formation, travel  more  easily  or  more  rapidly  than  others,  and 
some  are  more  intelligent  or  more  enduring  or  more  docile. 

1  See  data  from  Agricultural  Experiment  Station,  University  of  Illinois. 

7 


8  VARIATION 

Some  dogs  (bloodhounds)  trail  marvelously  well ;  others  (grey- 
hounds) scarcely  at  all.  Some  hens  lay  more  eggs  than  others, 
and  of  different  color  and  size. 

Some  animals  are  hard  feeders,  while  others  lay  on  flesh 
readily.  Some  beef  is  coarse  in  its  grain  ;  other  is  fine  and  ten- 
der. Some  is  well  marbled  with  fat ;  other  is  not.  Sometimes 
the  flavor  is  delicate  ;  again  it  is  rank,  and  often  it  is  insipid. 

No  two  trees  are  alike  in  their  growth  or  branching  habit, 
though  similar  within  the  same  variety,  and  the  widest  difference 
is  often  found  in  leaves  from  the  same  tree. 

Differences  extend  to  minute  particulars  and  include  all  charac- 
ters. The  student  should  early  form  a  clear  conception  of  the 
fact  that  differences  extend  to  all  characters  however  insignifi- 
cant or  minute.  Besides,  he  should  understand  that  they  include 
function  as  well  as  structure,  and  that  not  only  external  anatomy 
and  conformation  are  involved  but  internal  organs  and  their 
activity  as  well,  and  no  greater  mistake  can  be  made  than  to 
define  evolution  as  "a  study  in  morphology." 

If  we  so  define  the  word  "  variation  "  as  to  cover  any  change 
in  detail  of  structure  or  function  which  our  faculties  enable  us 
to  detect,  then  we  may  say  that  variation  extends  to  all  charac- 
ters, internal  or  external,  structural  or  functional,  and  if  the 
study  lay  in  the  realm  of  ethics,  economics,  philosophy,  or  reli- 
gion, we  should  add,  material  or  immaterial. 

The  individual  is  therefore  so  distinctly  a  unit  that  its  iden- 
tity is  at  once  recognized  and  the  principle  is  conceded  that  "  no 
two  are  alike  "  and  that  variation  is  universal. 

Limitation  of  variability.  The  exception  to  the  universality 
of  variability  is  in  the  realm  of  non-living  matter.  The  specific 
gravity  and  other  properties  of  iron,  gold,  sodium,  or  chlorin 
are  constant,  and  their  relations  and  combining  powers  with 
other  chemical  substances  are,  under  identical  conditions,  invari- 
able and  therefore  well  known. 

Oxygen,  hydrogen,  and  even  nitrogen  and  carbon,  combine 
always  in  definite  proportions,  and  though  their  combinations 
are  exceedingly  numerous  yet  when  the  conditions  are  known 
the  exact  combination  can  be  foretold  ;  moreover  the  properties 
of  this  combination  will  not  only  be  definite  but  they  will  be 
identical  with  those  of  all  other  similar  compounds.  In  this 


VARIATION   IN   GENERAL  9 

way  sodium  chlorid,  for  example,  has  always  definite  and  well- 
known  properties  not  subject  to  variability. 

It  is  to  be  noted  of  course  that  the  properties  of  the  com- 
pound NaCl  are  totally  different  from  the  properties  of  the  ele- 
ments that  compose  it,  Na  and  Cl.  They  are  nevertheless  distinct 
and  invariable  as  well  as  new.  This  distinction  between  the  varia- 
bility of  living  matter  and  the  constancy  of  non-living  matter 
should  be  borne  in  mind  later  on  when  discussing  some  of  the 
causes  of  variation. 


SECTION   II— VARIABILITY  THE  BASIS  FOR 
IMPROVEMENT 

Improvement  is  possible  only  where  variability  exists.  The 
compound  NaCl  being  constant,  it  would  be  impossible  to  pro- 
duce an  improved  variety  of  sodium  chlorid,  because  the  com- 
pound is  always  the  same  and  cannot  be  had  with  other  than  its 
standard  and  invariable  properties.  Improvement  in  this  com- 
modity is  limited,  therefore,  to  its  mechanical  form  and  cannot 
extend  to  its  constitution. 

Living  matter,  upon  the  other  hand,  while  possessed  of  defi- 
nite properties,  does  not  exhibit  these  properties  always  in  the 
same  degree,  and  observation  and  experience  have  both  shown 
that  profound  changes  may  be  made  in  either  the  form  or  the 
constitution  of  both  plants  and  animals  by  the  simple  method  of 
judicious  combinations  of  desirable  deviations. 

If  there  were  no  variability,  and  if  living  matter  were  as  con- 
stant in  its  properties  as  is  non-living  matter,  then  we  should  be 
certain  of  what  we  already  have,  but  no  improvement  would  be 
possible.  As  it  is,  with  variability  everywhere,  living  organisms 
are  both  capable  of  improvement  and  liable  to  degeneration,  for 
both  are  the  logical  consequence  of  variability.  Man  must  there- 
fore work  for  what  he  possesses  in  the  way  of  animals  and 
plants,  and  they  will  serve  him  well  or  ill  according  to  his  knowl- 
edge and  skill  in  dealing  with  their  variations.. 

Accordingly  he  cannot  know  too  much  about  the  variations  that 
are  likely  to  occur,  — their  nature,  their  extent,  and  the  causes 
that  control  their  appearance  and  determine  their  permanency. 


10  VARIATION 

He  cannot  know  too  much  about  life  and  its  vicissitudes,  about 
living  things  and  what  they  do. 

An  animal  is  born  into  the  world.  Its  energies  are  first 
devoted  to  nutrition  and  growth.  It  builds  its  own  machine 
and  builds  it  quickly  out  of  materials  lying  close  at  hand.  In 
good  time  it  is  finished  and  all  its  energies  are  at  a  maximum. 
It  seems  like  a  stable  thing  that  must  live  forever.  But  repro- 
duction occurs,  securing  a  succession  of  its  kind.  One  after 
another  of  its  faculties  fail,  and  its  condition  is  again  reduced  to 
that  of  bare  existence,  with  youthful  recuperative  powers  gone 
forever.  By  and  by  some  vital  function  fails.  Then  life  goes 
out ;  the  organism  breaks  down  and  returns  its  elements  to  the 
inorganic  world.  Such  is  the  brief  history  of  a  bit  of  matter 
temporarily  endowed  with  life, — fleeting  as  a  breath;  any 
service  it  may  render  us  must  be  caught  in  the  passing. 

SECTION  III  —  NATURE  OF  VARIABILITY 

The  exact  nature  of  variability  is  a  most  obscure  subject, 
and  one  that  cannot  be  fully  comprehended  in  the  present 
state  of  knowledge.  Whether  the  distinctions  between  living 
and  non-living  matter  will  always  remain  as  marked  as  they 
now  seem  to  be,  only  future  discoveries  will  determine.  We 
have  as  yet  only  touched  the  fringe  of  this  great  subject,  but 
enough  is  known  to  enable  us  to  begin  to  penetrate  some  of  its 
mysteries. 

At  least  two  general  principles  may  be  laid  down  in  the 
present  state  of  knowledge  without  much  chance  of  error : 

1.  That  all  characters  of  plant  and  animal  life,  whether  struc- 
tural or  functional,  are  exceedingly  variable. 

2.  That  ordinary  variation  is  the  result  of  a  change  in  the 
relations  between  a  number  of  associated  characters  through  the 
deviation  of  one  or  more  of  the  members,  and  not  the  introduc- 
tion of  an  absolutely  new  character. 

We  speak  loosely  of  "  introducing  new  characters,"  but  in 
truth  improvement  consists,  not  in  the  introduction  of  absolutely 
new  characters,  but  in  the  intensifying  of  desirable  old  ones  and 
the  subordination  of  those  that  are  undesirable.  For  example, 


VARIATION    IN   GENERAL  II 

when  we  undertake  to  improve  the  quality  of  wool  we  limit  our 
attempts  to  the  sheep,  with  which  wool  bearing  is  a  natural 
character.  Whether  the  horse  or  the  hog  could  be  made  to  grow 
wool  is  a  question.  If  the  hen  could  be  made  to  produce  milk 
or  the  cow  to  grow  feathers,  that  would  be  the  introduction  of 
a  new  character  in  the  strictest  sense  of  the  term. 

But  nothing  similar  to  this  has  ever  been  accomplished  by  man. 
The  particular  group  of  characters  that  constitutes  a  given  species 
appears  to  be  strangely  fixed,  and  improvement  seems  to  con- 
sist in  changing  the  relations  of  these  characters  among  them- 
selves rather  than  in  the  introduction  of  new  members.  How 
this  particular  grouping  arose  originally  and  how  a  new  member 
(character)  might  be  introduced  are  questions  for  the  student  of 
general  evolution.  They  are  questions,  moreover,  upon  which  the 
present  state  of  knowledge  sheds  little  light,  and,  so  far  as  is 
known,  the  study  of  the  practical  breeder  is  limited  to  methods 
of  dealing  with  groups  of  characters  already  associated  and  con- 
stituting well-marked  types  and  forms. 

SECTION  IV  — MEANING  OF  THE  TERM  "CHARACTER" 

This  is  a  much-abused  term,  loosely  used  in  a  variety  of  mean- 
ings. For  example,  when  an  individual  differs  slightly  from 
another  we  say  he  has  different  characteristics..  What  we  really 
mean  is  simply  that  his  characters  differ  in  their  development, 
not  that  he  has  different  characters.  His  bone  is  not  so  round 
or  his  hock  so  crooked  ;  the  crops  are  not  so  full  or  the  milk  so 
rich  ;  the  eye  of  the  potato  is  not  so  sunken  or  the  color  of  the 
fruit  so  high  in  one  specimen  as  compared  with  another,  and 
we  say  loosely  that  the  characters  are  different. 

Now  the  truth  is  the  characters  are  not  different  in  kind  but 
only  in  degree  and  proportion.  We  say  of  one  horse  that  he  has 
speed  and  of  another  that  he  has  not  speed.  The  fact  is  that 
they  both  have  some  speed,  but  only  one  has  enough  to  attract 
attention  and  be  worthy  of  remark.  This  use  of  terms,  unfortu- 
nate as  it  may  be,  is  probably  too  common  to  be  changed  ;  indeed, 
the  mere  use  of  terms  is  of  less  importance  than  a  clear  compre- 
hension of  the  facts. 


!  2  VARIATION 

The  term  "  character  "  is  employed  in  this  text  to  designate  one 
of  those  details  of  form  or  function  which,  taken  together,  consti- 
tute a  well-marked  group  of  animals  or  plants  more  or  less  closely 
related  by  descent,  and  this  is  the  only  sense  in  which  the  term 
ought  to  be  used.  Thus  the  color  characters  of  the  horse  are 
black,  bay,  brown,  gray,  etc.,  but  not  red,  green,  or  blue,  although 
these  characters  are  not  unknown  to  the  animal  world,  being 
common  with  birds. 

Used  in  this  sense,  a  "character"  belongs  primarily  to  the 
race  or  group  of  which  the  individual  is  a  member.  It  is  there- 
fore not  peculiar  to  any  particular  individual  and  is  in  no  sense 
personal  property.  Thus  not  only  the  color  of  the  coat  but  the 
form  of  the  body,  the  peculiar  function  of  any  of  its  organs,  as  in 
milk  production  or  the  secretion  of  poisons,  any  special  mental 
attitude  or  intellectual  function,  or  even  a  particular  crook  of 
limb  or  special  body  marking  of  any  kind  that  runs  commonly 
through  the  groups,  is  properly  spoken  of  as  a  racial  character. 
Those  characters  do  not  come  and  go,  but  on  the  contrary  they 
remain  with  the  race  indefinitely.  The  individual  horse,  for 
example,  will  be  marked  by  one  or  possibly  more  of  the  color 
characters  of  his  kind,  —  black,  white,  bay,  etc.,  —  but  he  will 
not  be  marked  with  characters  not  of  his  kind,  as  red,  green, 
etc.  From  this  we  see  that  the  individual  is  not  so  good  a 
unit  for  study  as  is  the  group  to  which  he  belongs  and  the  racial 
characters  that  compose  it. 

Now  the  personality  of  the  individual  so  strongly  impresses 
us  that  we  instinctively  regard  him  as  an  actual  unit,  and  we 
speak  loosely  of  his  characters  as  if  they  were  personal  property 
peculiar  to  this  individual  alone,  whereas  he  possesses  nothing 
that  is  not  common  to  his  race.  His  differences  are  in  degree, 
not  in  kind. 

What  we  mean  to  designate  in  the  individual  is  the  particular 
combination  of  racial  characters  that  make  up  his  personality, 
knowing  perfectly  well  that  the  characters  of  all  individuals  within 
the  race  are  racial  characters  and  no  other,  and  that  every  indi- 
vidual that  may  ever  arise  by  descent  will  be  limited  as  to  his 
details  to  some  combination  of  the  characters  of  his  race.  Now 
the  characters  of  any  race  are  so  many,  their  deviations  are  so 


VARIATION   IN  GENERAL  13 

wide,  and  their  power  to  move  independently  of  one  another  ie 
so  great  that,  according  to  the  doctrine  of  probabilities,  an  almost 
infinite  variety  of  combinations  is  possible.  Hence  no  two  indi- 
viduals are  ever  likely  to  be  identical.  We  thus  arrive  at  the 
conclusion  that  the  proper  study  of  the  breeder  is  not  so  much 
the  individual  as  it  is  the  normal  characters  of  the  race  to  which 
he  belongs. 


SECTION  V  — DOMINANT  AND  LATENT  CHARACTERS 

The  race  as  a  whole  clearly  possesses  more  characters  than  can 
ever  be  utilized  in  the  visible  make-up  of  any  single  individual. 
Among  all  the  colors  of  horses,  but  one,  or  at  most  two,  can  be 
found  in  any  special  instance.  The  race  is  therefore  a  kind  of 
composite  of  all  the  individuals  that  compose  it,  or,  more  properly 
speaking  for  purposes  of  study,  it  affords  a  wide  assortment  of 
elements  out  of  which  individuals  are  composed. 

The  individual  transmits  the  characters  of  the  race.  If  the 
group  of  characters  constituting  a  species  is  larger  than  that 
constituting  an  individual,  as  with  color  among  horses ;  and  if 
an  individual  may  transmit  a  character  which  (apparently)  he  does 
not  possess,  and  experience  shows  that  he  does,  then  it  follows  . 
that  the  individual  is  in  actual  possession  of  more  characters  than 
those  directly  involved  in  his  visible  make-up. 

For  example,  the  offspring  of  two  black  horses  will  likely  be 
black,  but  it  may  be  bay,  brown,  or  any  other  color  characteristic 
of  the  horse  kind.  It  is  safe  to  say  that  it  will  not  be  red,  green, 
or  blue,  because  these  colors  are  known  not  to  belong  to  the 
horse  kind,  though  all  are  freely  found  in  nature. 

Milk  secretion  is  confined  to  the  female  sex,  yet  a  bull  whose 
dam  is  a  heavy  milker  will  transmit  milking  quality  almost  as 
successfully  as  will  a  cow.  In  this  instance  the  male  transmits  a 
quality  that  he  does  not  apparently  possess  and  that  could  not 
become  functional  in  his  case. 

From  this  we  infer  that  the  individual,  whatever  his  particu- 
lar make-up,  transmits  all  the  characters  of  the  race,  and  none 
other ;  and  that  he  is  therefore  possessed  of  all  the  racial  char- 
acters of  his  kind  in  some  degree  visible  or  potential.  From 


14  VARIATION 

this  we  conclude  that  the  apparent  make-up  of  the  individual 
depends  upon  the  particular  characters  that  happen  to  be 
strongest,  that  is,  most  highly  developed  in  his  case,  but  that 
he  is  in  actual  possession  and  may  transmit  any  and  all  the 
characters  of  the  race  to  which  he  belongs,  but  no  other. 

We  now  arrive  at  the  distinction  between  dominant  and  latent 
characters,  which  is  as  follows:  Those  characters  that  are  prom- 
inent in  any  individual  are  said  to  be  dominant  with  him  because 
well  developed  and  plainly  evident,  and  all  other  racial  charac- 
ters are  said  to  be  latent  because  not  evident,  although  they  are 
known  to  be  present  from  the  fact  that  they  are  transmitted  to 
the  offspring,  often  becoming  the  dominant  characters  in  future 
generations. 

The  term  "  latent"  should  not  convey  the  impression  of 
hidden  or  lurking  characters,  but  rather  undeveloped  possibil- 
ities of  the  race  within  the  individual  in  question.  With  this 
conception  the  student  will  be  saved  much  mental  confusion 
when  dealing  with  heredity  and  reversion. 

Elementary  characters.  In  a  biological  sense  the  ultimate 
unit  of  variability,  therefore,  must  be  something  less  than  the 
racial  characters  which  we  have  been  discussing,  because  they 
themselves  are  complex  rather  than  simple.  We  speak  of  the 
leg  of  a  horse  or  the  quality  of  milk  as  a  whole.  Even  if  we 
narrow  the  point  to  the  conformation  of  the  hock  or  the  propor- 
tion of  fat,  we  yet  have  characters  clearly  made  up  of  parts. 
The  hock  is  an  exceedingly  complex  structure,  and  seven,  pos- 
sibly nine  or  ten  fats  and  oils  are  found  in  the  fat  of  milk. 

As  almost'  unlimited  color  effects  are  made  up  by  few  pri- 
maries in  different  proportions,  and  as  all  ordinary  materials  are 
made  up  of  a  few  chemical  elements  in  different  combinations, 
so  in  all  probability  if  we  could  make  the  ultimate  analysis  we 
should  find  that  all  these  characters  are  made  up  of  definite  liv- 
ing units,  that  we  may  call,  for  want  of  a  better  name,  elementary 
characters. 

These  elementary  characters  have  received  many  and  various 
names.  They  are  the  stirp  of  Galton,  the  biophors  of  Weismann, 
and  the  physiological  units  of  biologists  generally.  In  general 
they  are  the  smallest  conceivable  living  units,  comparable  with 


VARIATION   IN   GENERAL  15 

the  molecule  of  chemical  compounds.  Such  elementary  charac- 
ters are  supposed  not  to  be  variable  except  as  they  effect  dif- 
ferent combinations  among  themselves. 

SECTION  VI— THE  UNIT  OF  VARIABILITY 

The  unit  of  variation  is  therefore  not  the  individual  but  the 
racial  characters  that  constitute  the  particular  group,  and  that 
run  down  the  line  of  descent  like  the  strands  of  a  rope  and  out 
of  which  individuals  are  made  up,  — some  with  one  combination, 
others  with  another,  after  the  fashion  of  threads  in  a  fabric, 
forming  patterns  here  and  there,  now  of  one  design  now  of 
another,  as  they  wander  apparently  aimlessly  here  and  there.1 

It  is  evident,  however,  that  the  actual  basis  of  character  devia- 
tion is  sometimes  exceedingly  complex.  Milk  secretion,  for 
example,  while  limited  to  certain  animals  and  confined  to  the 
female  sex,  is  properly  recognized  as  a  distinct  character ;  yet 
its  successful  functioning  depends  upon  a  variety  of  considera- 
tions,—  the  general  health  of  the  body,  the  nervous  tempera- 
ture of  the  individual,  the  power  of  the  stomach  to  provide  large 
quantities  of  prepared  food,  the  ability  of  the  kidneys  to  do 
their  work,  and  the  power  of  every  organ  in  the  body  to  dis- 
charge its  function  successfully  and  fully  under  heavy  strains. 
All  these  are  as  important  to  successful  milk  production  as 
are  large  and  active  milk  glands,  and  an  accident  at  any  point 
will  cause  deviation  in  milk  yield  either  as  to  quantity  or  quality 
or  both. 

Deviation  in  color,  on  the  other  hand,  may  be  due  to  presence 
or  absence  of  pigment,  which  may  be  regarded  as  a  chemical 
substance  secreted  at  a  single  point.  In  this  and  in  similar 
cases  the  actual  basis  of  deviation  is  simple  and  readily  detected. 
From  this  it  will  appear  that  the  ultimate  seat  of  variation, 
whose  fluctuations  are  responsible  for  character  deviations,  may 
be  exceedingly  difficult  if  not  impossible  to  identify. 

1  The  unit  of  variability  must  not  be  confused  with  the  unit  of  selection  :  the 
latter,  of  course,  is  the  individual.  We  cannot  separate  his  characters,  but  must 
take  him  as  he  is,  for  better  or  for  worse  ;  but  we  must  do  so  fully  realizing  that 
each  of  his  separate  characters  has  an  identity  of  its  own,  so  that  the  unit  of  vari- 
ability is  far  within  the  necessary  unit  of  selection. 


1.6  VARIATION 

It  has  been  assumed  that  the  ultimate  unit  of  organized 
beings  is  the  cell.  This  is  true  in  a  structural  sense  only,  for 
there  is  positive  evidence  that  the  cell  is  itself  made  up  of 
various  and  distinct  elements,  capable  of  somewhat  independent 
action  in  both  cell  division  and  growth.  The  content  of  a  cell 
is  not  to  be  regarded  as  a  mass  of  amorphous  protoplasm  to  be 
halved  or  quartered  by  chance,  but  on  the  contrary  it  is  an 
organized  body  with  a  distinct  difference  between  the  nucleus 
with  its  definite  number  of  chromosomes  (the  supposed  seat  of 
the  physiological  units  that  give  character  to  its  activities)  and 
its  surrounding  cytoplasm  or  food  material. 

Again,  a  whole  group  of  similar  cells  may  constitute  a  special 
organ  (liver,  kidney,  or  heart),  discharging  a  highly  specialized 
function  quite  different  from  that  of  any  other  portion  of  the 
body.  This  colony  of  many  cells  discharging  the  same  function 
appears  to  move  together,  thus  constituting  a  kind  of  functional 
unit  larger  than  and  quite  distinct  from  the  ultimate  physio- 
logical units  that  must  reside  within  the  cell. 

Correlated  variation.  Still  again,  it  is  found  in  practice  that 
occasionally  whole  groups  of  characters  seem  to  be  so  correlated 
as  to  move  together,  so  that  having  found  one  we  may  reason- 
ably expect  to  discover  the  other.  Familiar  examples  of  this 
'are  found  in  nearly  all  cases  of  reversion.  For  instance,  a  white 
calf  among  Devon  cattle  will  almost  certainly  show  black  or 
brown  points  (ears,  nose,  and  legs),  while  a  white  shorthorn  will 
not.  The  one  is  a  case  of  reversion  to  the  ancestral  color  of  the 
breed,  —  the  wild  cattle  of  Britain;  the  other  is  simply  the 
appearance  of  one  of  the  normal  color  characters  of  the  race. 
In  increase  of  numbers  of  parts  there  is  some  tendency  to  repeat 
a  whole  group,  as  in  cases  of  "  double  hand." l 

The  same  tendency  for  many  distinct  characters  to  move 
together  in  groups  is  found  in  cases  of  so-called  "  sports,"  in 
which  we  instinctively  recognize  something  more  than  ordinary 
variation. 

These  instances  of  grouping  of  characters  normally  independ- 
ent in  such  a  way  as  afterward  to  move  together  is  to  be  dis- 
tinguished from  such  variation  as  is  involved  in  extreme  milk 

1  See  under  Meristic  Variation. 


VARIATION   IN   GENERAL  1 7 

production,  in  which  results  are  to  be  ascribed  rather  to  fortui- 
tous variations  among  independent  units  than  to  anything  like  a 
linking  together  of  the  separate  characters  involved. 

The  ultimate  unit.  The  student  must  maintain  a  clear  vision 
as  to  distinctions  of  this  sort.  From  the  biological  standpoint 
we  accept  as  the  unit  of  variability  the  ultimate  physiological 
units  that  must  reside  within  the  cell ;  for  purposes  of  everyday 
use,  however,  we  assume  as  a  unit  that  detail  of  form  or  function 
that  is  important  to  the  breeder,  understanding  perfectly  well 
that,  considered  physiologically,  it  doubtless  consists  of  a  num- 
ber of  ultimate  units  which,  like  the  elements  in  a  chemical  com- 
pound, are  entirely  capable  of  other  and  distinct  combinations. 

To  repeat,  we  may  assume  either  one  of  these  conceptions  as 
the  unit  for  study  according  to  the  purpose  in  hand.  In  the 
text  the  word  "  character  "  will  be  used  to  denote  that  detail  of 
(racial)  structure  or  function  which  is  important  to  the  farmer 
and  to  this  study.  The  character  will  be  considered  as  the 
practical  unit  of  variation,  knowing  perfectly  well  that  the  ulti- 
mate unit  of  variability  lies  much  farther  back  in  the  constitution 
of  the  protoplasm  itself.  When  this  is  in  mind  the  terms  "  ele- 
mentary character,"  "  physiological  unit,"  or  some  equivalent 
term  will  be  used. 

Whatever  the  situation,  the  student  must  not  consider  the 
individual  as  the  unit  of  variability  or  he  will  come  to  grief  both 
in  study  and  in  practice,  nor  should  he  become  confused  by 
those  occasional  and  remarkable  correlations  of  characters  that 
suggest  a  unit  of  variability  unduly  large. 

SECTION  VII  —  DISTINCTIONS  AS  TO  KINDS  OF 
VARIATIONS 

In  the  critical  study  of  variation  it  is  necessary  to  observe 
certain  distinctions  that  are  often  overlooked,  resulting  in  more 
or  less  confusion  as  to  what  is  really  involved  in  the  term 
"variation." 

Variation  quantitative  or  qualitative.  The  first  question  that 
should  arise  in  the  mind  of  the  student  touching  any  deviation  is 
this :  Is  the  difference  one  in  degree  merely  (quantitative)  or 


!$  VARIATION 

is  it  a  difference  in  kind  (qualitative)  ?  For  example,  one  horse 
is  exactly  like  another,  only  larger :  the  difference  is  quanti- 
tative. Another  is  no  larger,  but  he  can  draw  more  and  has 
greater  endurance :  the  difference  is  qualitative.  One  cow  gives 
more  milk  than  another :  the  difference  is  quantitative  ;  but  a 
third  gives  better  milk,  and  the  difference  is  qualitative.  One 
apple  is  larger  than  another  of  the  same  variety  (quantitative 
variation),  but  another  is  different  in  texture  and  flavor  (quali- 
tative variation). 

When,  therefore,  in  the  study  of  a  racial  character  as  repre- 
sented in  the  same  or  in  different  individuals  it  is  found  to  have 
varied,  the  first  question  to  ask  and  answer  is  this  :  Is  the  devi- 
ation one  in  kind  or  merely  in  amount  ?  Is  it  qualitative  or  merely 
quantitative  ?  Is  the  change  to  be  regarded  as  one  in  nature  or 
only  in  degree  ?  If  the  student  will  carry  these  distinctions  always 
in  mind,  he  will  avoid  much  needless  confusion. 

Variation  continuous  and  discontinuous.  It  is  not  to  be  assumed 
that  variations  differ  from  one  another  by  infinitesimal  increments. 
The  differences  may  be  infinitesimal  (continuous  variation)  or  they 
may  be  "discrete  "  (discontinuous  variation). 

Darwin  supposed,  and  it  is  commonly  assumed,  that  variation 
is  by  nature  continuous,  and  that  new  forms  originate  by  the 
gradual  accumulation  of  insensible  differences  through  the  agency 
of  long-continued  selection.  This  means  that  if  all  the  individuals 
that  ever  lived  could  be  assembled  and  so  assorted  as  to  bring 
nearest  together  those  that  are  nearest  alike,  it  would  then  be 
found  that  they  would  grade  into  one  another  by  imperceptible 
differences,  and  that  any  gaps  that  might  occur  would  be  due  to 
the  effect  of  selection  in  blotting  out  intermediate  forms. 

Now  this  is  a  hasty  assumption,  indicating  in  these  days  but 
a  superficial  acquaintance  with  the  manner  of  variation.  We 
cannot  assume  that  all  possible  values  in  variable  characters  are 
presented  ;  indeed,  we  know  very  well  that  in  many  cases  all 
possible  values  are  not  presented,  and  that  some  intermediate 
forms  never  arise.  For  example,  peaches  often  give  rise  to 
nectarines,  but  there  is  a  gap  between  the  two  that  apparently  is 
never  filled.  Darwin  called  an  occurrence  of  this  kind  a  "sport," 
as  if  it  were  an  instance  in  which  all  ordinary  laws  were  set  aside, 


VARIATION    IN   GENERAL  19 

whereas  it  only  shows  that  the  variations  of  the  peach  are  often 
discontinuous,  with  wide  gaps  representing  spaces  not  filled  by 
variation. 

To  get  a  full  understanding  of  this  ground  the  student  must 
form  a  clear  conception  of  the  distinction  between  continuity  and 
discontinuity  as  used  in  this  connection. 

A  man  grows  from  childhood  to  maturity.  In  doing  so  he 
passes  through  all  possible  weights  and  heights  between  those  of 
infancy  and  maturity.  We  cannot  represent  all  these  values  by 
any  of  our  units  of  weight  or  measurements  because  all  numbers 
are  by  nature  discontinuous.  The  only  measure  of  continuity  is 
a  line,  because  a  line,  curved  or  straight,  represents  all  values 
sensible  and  insensible  between  its  two  extremes.  We  can  thus 
plot  continuity,  but  we  cannot  measure  it  except  by  cutting  it 
into  sections  and  measuring  it  at  stated  points  as  if  it  were  dis- 
continuous, ignoring  the  intervals. 

Changes  of  temperature  are  continuous,  as  are  those  of  humidity, 
illumination,  and  all  growth  in  the  sense  of  extension  in  size, 
whether  plant  or  animal.  All  motion,  whether  regular  or  irregular, 
is  continuous  because  all  intervening  spaces  are  included. 

Discontinuity,  on  the  other  hand,  implies  vacant  spaces  not 
represented  by  values.  The  good  singer  goes  abruptly  from  one 
note  to  the  next,  giving  a  discontinuous  series  of  tones,  while  the 
unskilled  vocalist  slides  up  or  down  the  scale,  giving  rise  to  a 
continuous  series  of  tones  in  his  effort  to  find  the  proper  note. 
The  latter  is  not  music  because  the  ear  is  not  pleasantly  affected 
by  this  confused  jumble  of  sound  waves  arising  from  the  inter- 
mediate tones.  Good  music  consists  of  a  series  of  tones  not 
flowing  into  one  another  but  cut  sharply  off  and  cast  into  a 
discontinuous  series,  striking  the  ear  at  intervals  with  sound 
waves  that  fit  with  mathematical  precision. 

All  number  is  by  nature  discontinuous.  By  fractions  we  attempt 
to  bridge  the  space  between  contiguous  units,  as  between  I  and 
2  ;  but  however  small  the  fraction,  there  is  yet  a  space,  and  a 
sensible  and  measurable  one,  between  the  fraction  and  the  next 
anit.  iT9_9^_9_  is  noj-  2)  nor  will  it  ever  become  2  this  side  of 
infinity  by  the  addition  of  any  number  of  nines  to  the  numerator 
and  ciphers  to  the  denominator.  It  will  constantly  approach  2, 


20 


VARIATION 


but  will  never  reach  it,  because  definite  number  is  discontinuous. 
This  is  why  we  can  never  accurately  measure  continuity  except 
by  a  line,  and  this  is  why  we  cannot  express  in  numbers  the 
growth  of  an  animal  or  plant,  except  approximately  in  terms  of 
discontinuity. 

All  chemical  compounds  are  made  up  of  elements  in  definite 
proportion.  They  are  therefore  discontinuous.  We  have  H2O 
and  H2O2,  but  no  intermediate  is  possible,  —  this  again  for  numer- 
ical reasons.  Plants  and  animals  generally  are  dimorphic,  the  one 
form  being  male,  the  other  female :  this  is  discontinuity.  Some 
species  are  trimorphic  or  even  polymorphic.  The  ant  is  either 
male,  female,  worker,  or  soldier,  and  though  they  all  belong  to 
the  same  species  there  are  no  connecting 
links  in  this  discontinuous  chain. 

Dimorphism  without  respect  to  sex  oc- 
curs in  many  beetles,  and  is  exceedingly 
marked  in  the  common  earwig,1  as  shown 
in  the  accompanying  diagram. 

The  shape  of  this  curve  shows  clearly 
that  here  are  two  distinct  forms  of  male, 
a  large  and  a  small  one,  living  together 
and  arising  naturally  out  of  the  common 
mass,  yet  showing  almost  no  intermediates, 
nounced,  but  there  are        Students  of  breeding  familiar  with  the 
almost  no  intermediates,    older  types  of  Hereford  will  recall  that  the 
breed  was  almost  dimorphic  in  that  two  dis- 
tinct types  tended  to  appear  with  singular  perverseness,  refusing 
either  to  blend  or  to  undergo  modification.    There  was  the  old, 
large,  solid-bodied,  thick-meated,  deep-ribbed  type,  ideal  except 
as  to  lateness  of  maturity  ;  then  there  was  also  the  pony-built 
tvPe»  —  short  in  the  barrel  and  lacking  in  depth  behind,  though 
well  proportioned  in  front. 

The  shorthorns  are  almost  polymorphic  in  possessing  not  one 
but  a  variety  of  types,  each  standing  out  with  extreme  distinct- 
ness and  not  readily  merged. 

The  more  the  matter  is  examined  the  more  it  will  be  seen  that 
strange  and  unaccountable  gaps  are  found  everywhere.  Many  a 

1  Bateson,  Materials  for  the  Study  of  Variation,  pp.  36-42. 


FIG.  i.  Dimorphism  illus- 
trated :  two  types  of  the 
common  earwig.  B  is 


VARIATION   IN   GENERAL  21 

breeder  has  spent  his  life  and  his  substance  in  the  vain  attempt  to 
produce  a  desired  intermediate  between  two  forms,  either  one  of 
which  are  easily  secured.  The  question  arises,  therefore,  Are  some 
intermediates  impossible  ?  Can  we  bridge  the  space  between  the 
nectarine  and  the  peach  ?  between  the  apricot  and  the  plum  ? 

With  all  these  examples  before  us,  we  see  at  once  that  to  pro- 
ceed upon  the  theory  of  continuity  is  a  gratuitous  assumption 
not  borne  out  by  facts.  Force  and  physical  agents  generally  seem 
to  be  continuous  in  their  different  manifestations,  shading  one 
into  another  with  imperceptible  gradations  ;  but  organized  matter, 
living  or  non-living,  seems  to  be  constructed  upon  the  plan  of  dis- 
continuity, in  which  case  we  may  expect  to  find  differences  that 
are  easily  perceptible,  and  should  not  be  surprised  at  the  appear- 
ance of  wide  spaces  between  nearly  related  forms  or  at  these 
remarkably  distinct  gaps  that  often  occur  between  a  standard 
form  and  its  offset,  which  Darwin  called  a  "  sport  "  and  which  we 
in  these  days  call  a  "  mutant." 

With  this  view  of  the  case,  we  should  not  expect  to  find  all 
nature  united  by  imperceptible  gradations,  even  providing  all  living 
beings  past  and  present  could  be  assembled  and  assorted  according 
to  nearest  resemblances.  Realizing  the  discontinuous  nature  of 
all  chemical  combinations,  living  or  non-living,  we  should  expect  to 
find  notable  gaps  representing  spaces  not  taken  by  any  possible 
form,  and  appearing  quite  independent  of  any  selective  process. 

This  distinction  is  exceedingly  important  at  the  outset  of  this 
study.  If  all  variations  are  continuous,  then  all  shades  of  differ- 
ence, however  minute,  may  be  expected  to  occur  naturally,  and 
we  may  hope  to  secure  them  by  breeding.  If,  however,  some 
variations  are  discontinuous,  then  for  these  characters  minute 
gradation  is  impossible,  and  we  may  expect  descent  to  follow  along 
certain  lines  only. 

Most  of  the  conditions  of  life  are  without  doubt  naturally  con- 
tinuous in  their  variations.  This  is  certainly  true  of  temperature, 
moisture,  light,  and  food.  Discontinuity  must  therefore  arise  from 
within,  and  is  evidently  connected  with  the  nature  of  organisms. 
This  is  not  difficult  to  appreciate  when  we  recall  the  essential 
discontinuity  of  all  chemical  compounds  or  other  organizations 
built  upon  the  basis  of  distinct  units. 


22  VARIATION 

The  student  must  not  therefore  assume  the  possibility  of  inter- 
mediate gradations  and  insensible  differences  when  dealing  with 
biological  phenomena.  Many  of  these  differences  are  essentially 
and  necessarily  discontinuous.  It  remains  to  discover  which 
these  are  and  to  discover  the  bearing  of  discontinuity  upon  the 
results  to  be  accomplished  by  selection. 

If  all  variations  were  continuous  we  might  hope  to  be  able 
theoretically  to  accomplish  any  desired  result  and  secure  any 
desired  shade  of  difference  by  selection ;  but  if  not,  then  there 
will  remain  notable  gaps  that  cannot  be  filled.  The  natural  corol- 
lary of  all  this  is  that  we  can  accomplish  by  selection  almost  any 
desired  shade  of  result  with  those  variations  which  are  by  nature 
continuous,  but  that  with  those  variations  which  are  by  nature 
discontinuous,  our  efforts  in  this  respect  will  be  limited. 

Distinctions  arising  from  the  nature  of  the  characters  involved. 
Having  determined  whether  the  deviation  is  quantitative  or  quali- 
tative, continuous  or  discontinuous,  we  next  inquire  into  the  real 
nature  of  the  variation  as  it  affects  the  organism.  Manifestly 
this  depends  upon  the  character  or  characters  involved. 

Those  concerned  with  form  will,  in  their  deviations,  give  rise  to 
morphological  differences.  On  the  other  hand,  deviation  in  char- 
acters distinctly  functional  will  give  rise  to  differences  in  organic 
activity  without  regard  to  form. 

Accordingly  four  distinctly  different  kinds  of  variation  are 
recognized : 

1 .  Morphological,  relating  to  differences  in  form  or  size.    By 
nature  they  are  always  quantitative,  but  may  be  either  continuous 
or  discontinuous. 

2.  Substantive,  relating  to  differences  in  quality  of  the  struc- 
ture as  distinct  from  mere  form  or  size.    By  definition  they  are 
always  qualitative  and  generally,  if  not  always,  continuous. 

3.  Meristic,  relating  to  deviations  in  pattern,  especially  as  to 
repeated  parts,  as  in  extra  fingers  and  toes,  doubling  of  petals, 
stooling  of  grain,  etc.    Variations  of  this  kind  are  either  quanti- 
tative or  qualitative,  generally  the  former,  but  are  of  necessity 
discontinuous. 

4.  Functional,  relating  to  deviations  in  the  normal  activity  of 
the  various  organs  and  parts  of  the  body  or  the  plant,  such  as 


VARIATION    IN   GENERAL 


23 


muscular  activity,  glandular  secretions,  etc.  They  are  either 
quantitative  or  qualitative,  continuous  or  discontinuous,  though 
rarely  the  latter. 

A  clear  understanding  of  these  distinctions  is  necessary  to  an 
intelligent  study  of  the  nature  and  causes  of  variation.  Accord- 
ingly enough  attention  will  be  given  to  each  to  acquaint  the 
student  with  the  way  in  which  variation  behaves,  partly  for  its 
own  sake  and  partly  as  preparation  for  careful  inquiry  into 
methods  of  dealing  with  deviations  in  those  plants  and  animals 
that  we  have  domesticated  and  appropriated  to  our  use,  and 
which  we  would  see  still  better  adapted  to  the  purposes  of  man. 

Summary.  Variability  is  the  universal  rule  among  living 
beings.  Literally  no  two  are  alike.  The  differences  extend  to 
all  characters  and  to  the  most  minute  particulars.  Non-living 
compounds  exist  in  definite  proportions,  and  their  qualities  are 
constant,  not  variable.  Variability  is  the  only  basis  for  improv- 
ment.  No  improvment  is  possible,  in  the  strictest  sense  of  the 
term,  with  respect  to  inorganic  compounds,  but  living  matter  being 
variable  is  capable  of  change  and  therefore  of  improvement. 

Variation  consists  not  in  the  introduction  of  new  character^ 
but  in  different  proportions  or  relations  among  the  old  ones. 
All  characters  are  racial,  and  all  individuals  actually  possess  all 
the  characters  of  the  race  and  none  other.  This  is  shown  by  the 
characters  that  are  transmitted  to  the  offspring. 

The  unit  of  variability  is  in  no  sense  the  individual,  though  he 
must  be  accepted  as  the  unit  for  selection.  The  real  unit  of  devia- 
tion is  the  racial  character,  but  back  of  that,  in  a  biological  sense, 
lie  the  elementary  characters  or  physiological  units,  whose  vari- 
ous combinations  constitute  racial  characters. 

Variation  is  both  quantitative  and  qualitative,  both  continuous 
and  discontinuous,  and  these  distinctions  should  be  clearly  in 
mind  at  all  times. 

SPECIAL  EXERCISES 

Prepare  a  list  of  variations  that  are  (i)  quantitative,  (2)  qualitative, 
(3)  morphological,  (4)  substantive,  (5)  meristic,  (6)  functional,  (7)  con- 
tinuous, (8)  discontinuous. 


24  VARIATION 

ADDITIONAL  REFERENCES 

ANIMALS  AND  PLANTS  UNDER  DOMESTICATION.  By  Charles  Darwin. 
2  vols. 

DISCONTINUOUS  VARIATION.  (An  example.)  By  E.  R.  Saunders.  Pro- 
ceedings of  the  Royal  Society,  LXII,  11-25. 

ORIGIN  OF  SPECIES  BY  MEANS  OF  NATURAL  SELECTION.  By  Charles 
Darwin,  i  vol. 

THEORY  OF  ORGANIC  VARIATION.    By  H.   S.  Williams.    Science,  VI, 

73-84. 
TYPE,  How  FIXED.    (On  genetic  energy  of  organisms.    Is  variability  and 

not  permanency  the  normal  law  of  organic  life?)    By  H.  S.  Williams. 

Science,  VII,  721-729. 
VARIATION  AND  SOME  PHENOMENA  CONNECTED  WITH  REPRODUCTION 

AND  SEX.    By  Adam  Sedgwick.    Science,  XI,  881-894,  923-930. 
VARIATION    DISCONTINUOUS.  '  (Study  of  a  recent  variety  of  flatfish.)     By 

H.  C.  Bumpus.    Science,  VII,  197. 
VARIATION  IN  PLANTS.    (A  study  of  the  portions  of  a  leaf  on  which  chlo- 

'  rophyll  is  found.)    Experiment  Station  Record,  XIII,  423. 
VARIATION  IN  TRILLIUM  GRANDIFLORUM.    (A  record  of  the  variations 

observed  in   185   cases.)     By   H.   W.  Britcher.     Maine    Experiment 

Station  Bulletin  No.  86,  pp.  169-196  ;  also  Experiment  Station  Record, 

XIV,  634. 


CHAPTER  II 

MORPHOLOGICAL    VARIATION 

Morphological  variation  has  reference  to  differences  in  form.  If 
two  or  more  individuals  possess  the  same  structural  characters  and 
if  they  have  all  attained  the  same  relative  development,  then  the 
different  individuals  will  differ  only  in  size  ;  but  if  the  characters 
have  not  attained  proportional  development  in  the  different  indi- 
viduals, then  we  shall  note  differences  in  form  independent  of 
mere  size.  This  is  the  simplest  of  all  forms  of  variation  and  is 
the  one  chiefly  in  the  mind  of  older  biologists,  even  leading  to 
the  mistake  of  supposing  that  evolution  is  essentially  a  study  in 
morphology. 

The  cause  of  morphological  differences  may  lie  in  extremely 
favorable  or  unfavorable  conditions  of  life,  especially  as  regards 
food  and  climate,  affecting  different  characters  differently,  or 
they  may  arise  from  internal  and  constitutional  causes,  as  in 
giants  and  dwarfs,  or  in  such  extreme  differences  as  in  the  mul- 
berry leaves  shown  in  Fig.  2. 

Instances  of  morphological  variation  are  so  common  and  so 
easily  noted  as  to  scarcely  require  mention.  Two  apples  are 
exactly  alike  except  that  one  is  larger  than  the  other.  It  is  a 
clear  case  of  morphological  variation.  In  this  instance  there  is 
no  difference  in  the  characters  of  the  two  individuals  except  that 
cell  division  and  growth  have  proceeded  farther  in  one  case  than 
in  the  other.  Aside  from  this  they  are  identical.  If  two  stalks 
of  corn  or  if  a  number  of  pigs,  sheep,  cows,  or  horses  are  exactly 
alike  except  as  to  size,  then  their  differences  are  quantitative 
only,  and  the  effect  is  morphological  merely. 

Again,  two  horses  are  of  the  same  breed, — that  is,  possess  the 
same  characters,  —  but  their  characters  are  not  equally,  that  is, 
proportionately,  developed.  In  one  the  leg  is  longer,  the  hock 
shorter,  or  the  face  wider  between  the  eyes.  These  differences 

2.S 


FIG.  2.    Morphological  variation  illustrated  :  different  forms  of  mulberry 
leaves  picked  from  the  same  tree  on  the  same  day      . 


MORPHOLOGICAL  VARIATION  27 

are  all  quantitative  and  morphological,  but  they  influence  form 
rather  than  size  as  a  whole,  because  their  development  is  not 
proportional  one  part  with  another. 

Variation  seldom  simple.  Instances  of  the  above  kind  are, 
however,  extremely  rare.  Variation  is  so  common  that  other 
differences  generally  accompany  those  of  form.  The  two  apples 
may  differ  in  color,  flavor,  or  texture  as  well  as  in  size,  in  which 
case  substantive  variation  has  also  occurred.  One  of  the  horses 
may  have  an  extra  rib,  one  of  the  pigs  a  solid  hoof,  or  one  of 
the  sheep  more  fibers  of  wool  to  the  square  inch,  in  which  case 
meristic  variation  is  present.  The  pulse  of  one  of  the  horses 
may  be  faster  than  that  of  the  other,  or  the  milk  of  one  cow 
may  be  richer  in  fat,  showing  functional  deviation. 

And  so  it  is  in  practice  that  two  or  more  forms  of  variation 
may  be  and  likely  will  be  found  present  in  the  same  individual. 
But  however  that  may  be,  all  differences  in  form  or  size  are 
regarded  as  morphological,  no  matter  what  other  differences 
may  be  found,  and  it  is  important  that  the  student  early  form 
the  habit  of  distinguishing  clearly  between  the  different  kinds 
of  variation  present,  even  in  the  same  individual. 

The  limits  of  size.  Every  species  has  a  general  average  of 
size  to  which  most  individuals  closely  approximate.  A  few,  how- 
ever (giants),  greatly  exceed  this  size,  and  others  (dwarfs)  fall 
far  short  of  it.  All  investigators  agree  upon  the  conclusion  that 
this  difference  in  size  is  due  to  the  number  and  not  the  size 
of  individual  cells ;  in  other  words,  size  is  dependent  upon  the 
energy  of  cell  division.1  This  energy  is  exceedingly  active  in 
youth,  gradually  decreasing  to  zero  at  maturity,  except  as  to 
certain  parts  (reproductive  organs,  skin,  and  sometimes  the 
teeth  and  horns).  In  most  species  accident  to  a  part  will  stim- 
ulate cell  division,  leading  to  a  more  or  less  successful  regenera- 
tion. For  the  most  part,  however,  cell  division  does  not  proceed 
rapidly  after  maturity,  and  the  limit  of  its  activity  is  in  general 
the  limit  of  growth.  Giants  therefore  represent  excessive  cell 
division  above  the  normal,  and  dwarfs,  arrested  development,  — 
an  abnormally  early  cessation  of  cell  division. 

1  Wilson,  The  Cell  in  Development,  pp.  388-394. 


28  VARIATION 

The  causes  involved  in  this  abnormal  behavior  of  the  cell  in 
division  are  exceedingly  obscure.  They  are  certainly  sometimes 
connected  with  food  and  care  in  early  life,  and  no  doubt  they 
are  often  constitutional.  Every  stockman  knows  about  the 
stunted  pig,  calf,  or  colt,  and  that  it  sometimes,  but  rarely, 
recovers;  that  is  to  say,  cell  division  once  checked  does  not  easily 
return  to  the  normal  rate.  The  trait,  however,  easily  becomes 
constitutional  and  hereditary,  for  whole  families  (strains)  become 
undersized  and  others  as  much  above  the  medium. 

Energy  of  growth  not  to  be  confused  with  bodily  or  func- 
tional activity.  While  the  larger  animal  of  his  kind,  whether 
it  be  the  individual  or  the  strain,  represents  the  greater  energy 
of  cell  division  in  body  building,  it  by  no  means  follows  that 
the  body  when  built  will  possess  a  greater  degree  of  activity 
than  will  its  normal  or  smaller  neighbor  ;  indeed,  the  opposite  is 
likely  to  be  true,  because  the  larger  body  works  at  greater  dis- 
advantage, having  greater  inertia  to  overcome  and  more  dead 
weight  to  carry  about.  This  is  eminently  true  of  all  animals 
whose  service  involves  transporting  the  body  from  place  to 
place,  as  among  horses.  It  is  manifestly  impossible  for  a  heavy 
horse  to  equal  a  light  one  in  speed  without  the  expenditure  of 
far  more  power  in  doing  it.  This  is  not  only  because  of  the 
extra  weight  but  because  of  mechanical  disadvantages  as  well. 
In  activities  not  involving  motion  this  difference  in  size,  within 
reasonable  limits,  does  not  exist ;  small  men,  for  example,  are 
doubtless  no  more  and  no  less  intellectual  than  are  large  ones. 

Importance  of  morphological  variation.  Next  to  those  of  color, 
differences  in  size  are  the  most  noticeable  of  all  variations ;  but 
they  are  by  no  means  the  most  significant,  and  their  importance 
is  likely  to  be  greatly  overestimated.  Except  in  a  few  instances, 
as  with  draft  horses,  mere  size  is  of  far  less  consequence  than 
is  commonly  supposed. 

Generally  speaking,  it  is  some  quality  other  than  bulk  that 
determines  value,  and  it  will  be  fortunate  for  breeding  when  the 
popular  notion  that  "  the  biggest  is  the  best "  shall  have  passed 
away.  The  largest  apple  is  not  the  best  for  eating,  nor  the 
largest  bull  the  best  for  breeding  purposes.  However,  this  does 
not  free  the  student  and  breeder  from  considerations  of  size, 


MORPHOLOGICAL  VARIATION  29 

because  extremes  both  ways  are  in  most  cases  to  be  avoided, 
and  the  highest  excellence  and  the  most  reliable  breeders  will 
commonly  be  found  among  the  individuals  of  medium  size. 

Differences  in  form,  arising  from  relative  inequality  in  devel- 
opment of  structural  parts,  are  of  more  consequence  than  are 
differences  in  mere  bulk,  in  which  development  has  been  pro- 
portional. This  is  especially  true  in  horses,  in  which  differences 
in  relative  development  of  structural  parts  may  seriously  affect 
the  appearance  or  interfere  with  the  action  of  the  individual. 
And  so  it  is  that,  while  morphological  differences  are  of  far 
more  significance  to  the  student  of  general  evolution  than  they 
are  to  the  farmer,  they  yet  constitute  a  phase  of  variation  not 
to  be  overlooked  by  the  student  who  is  interested  in  the  improve- 
ment of  domesticated  forms. 


ADDITIONAL  REFERENCES 

DARWINIANA.    By  Asa  Gray,    i  vol. 

DARWINISM.    By  A.  R.  Wallace,    i  vol. 

EXPRESSION  OF  THE  EMOTIONS  IN   MAN  AND  ANIMALS.    By  Charles 

Darwin,    i  vol. 

FROM  GREEKS  TO  DARWIN.    By  H.  F.  Osborn.    i  vol. 
LAMARCK:   His  LIFE  AND  WORK.    By  A.  S.  Packard,    i  vol. 


CHAPTER  III 

SUBSTANTIVE  VARIATION 

Substantive  variation  has  reference  to  differences  in  quality 
as  distinct  from  form  or  size.  It  regards  the  composition  or 
make-up  of  the  body  or  its  members,  and  refers  to  the  constitu- 
tion, or  inherent  nature,  of  the  organism. 

Everybody  recognizes  differences  in  muscles,  whether  firm 
and  strong,  or  soft,  flabby,  and  weak.  We  distinguish  the  bone 
of  a  horse  as  dense  or  as  soft,  porous,  and  spongy.  The  horn 
of  the  hoof  is  hard  and  tough  or  soft  and  "  shelly." 

Meat  is  fine  in  grain  and  high  in  flavor  or  coarse  in  grain  and 
lacking  in  quality.1  It  is  either  juicy  and  rich  or  dry  and  taste- 
less. The  gamy  flavor  of  wild  meat,  both  of  mammals  and  birds, 
is  especially  tasteful  to  the  huntsman,  and  whether  due  to  breed- 
ing or  to  feed,  it  is  certainly  characteristic  of  wild  life  everywhere. 
No  two  cuts  of  meat  are  alike,  whether  wild  or  tame,  and  these 
differences  are  so  pronounced  as  to  be  commonly  recognized ; 
indeed,  language  abounds  in  adjectives  descriptive  of  differences 
in  quality  of  food  stuffs. 

At  one  time  milk  was  sold  on  the  quantitative  basis  only,  but 
now  the  per  cent  of  fat  is  the  basis  of  value.  The  intelligence  of 
an  animal  or  of  a  man  depends  less  upon  the  size  and  weight  of 
the  brain  than  upon  the  quality  of  the  brain  matter  and  the 
depth  of  the  convolutions. 

One  apple  is  sweet,  another  is  sour,  and  still  another  is  insipid. 
One  fruit  is  highly  flavored,  another  is  tasteless.  The  sugar  of 
beets,  of  cane,  and  of  maple  is  the  same  ;  but  the  two  former  are 
simply  sweet,  while  the  latter  is  accompanied  by  a  highly  volatile 
ether  that  adds  a  peculiarly  delicious  aroma.2 

1  Pigs  fed  heavily  on  cotton-seed  meal  make  a  pork  strongly  flavored  with 
cotton-seed  oil.    See  Grindley,  Journal  of  American  Chemical  Society,  Vol.  XXVII. 

2  Isolated  by  Kedzie,  of  the  Michigan  Agricultural  College,  from  samples  fur- 
nished by  the  author. 

3° 


SUBSTANTIVE   VARIATION  31 

The  sugar  content  of  beets  varies  from  4  or  5  per  cent  to  over 
20  per  cent.  It  is  also  exceedingly  variable  in  cane.  Wheat  is 
richer  in  protein  than  is  corn,  but  both  are  variable,  and  corn 
has  been  bred  with  a  protein  content  higher  than  that  of  wheat.1 

Plants  differ  in  their  ability  to  withstand  frost  as  do  animals  to 
resist  disease.  A  single  stalk  of  corn  may  remain  fresh  and  green 
when  all  its  neighbors  have  been  killed.  Certain  individuals  seem 
immune  to  particular  diseases,  and  appear  to  be  able  to  resist 
infection  indefinitely. 

Color  in  general  is  based  upon  definite  chemical  constituents 
or  upon  the  character  of  the  surfaces  presented  for  refraction  of 
light.  In  either  case  it  is  a  matter  of  inherent  quality  and  is 
substantive. 

Importance  of  substantive  variation.  The  significance  of  sub- 
stantive differences  depends  upon  the  instance.  Speaking  gen- 
erally, these  differences  are  of  high  value.  They  are  usually, 
though  not  invariably,  correlated  with  efficiency,  and  in  such  cases 
they  possess  a  utilitarian  interest. 

A  dense  bone  is  better  than  a  soft  and  fibrous  one.  Every- 
body prefers  a  good  apple  to  a  poor  one  ;  we  have  a  decided  pref- 
erence for  certain  aromas  ;  the  juicy,  highly  flavored  steak  is 
better  than  the  dry,  tough,  and  tasteless  one. 

Color  is  a  utility  character  among  flowers.  We  buy  them  for 
their  color,  their  form,  and  their  odor.  They  have  no  other  value, 
and  of  these  characters  their  coloring  is  of  the  most  importance. 

Color,  however,  is  in  general  the  most  deceptive  of  all  charac- 
ters, —  deceptive  because  it  is  striking  and  because  we  greatly 
prefer  certain  color  effects  over  others,  even  though  not  correlated 
with  utility.  We  carry  this  preference  beyond  reason.  A  red 
apple  will  sell  for  more  than  one  of  any  other  color ;  yet  vye  buy 
an  apple  not  to  look  at  but  to  eat ;  and  no  one  has  shown  a  cor- 
relation between  color  and  quality  in  fruit. 

Horses  with  white  skin  are  proverbially  subject  to  certain 
diseases.  For  this  and  other  reasons  color  has  no  little  signifi- 
cance in  horses,  but  among  cattle  it  has  practically  no  meaning 
whatever  ;  and  yet  how  decidedly  do  color  markings  figure  in 

1  The  lowest  protein  content  discovered  in  the  breeding  experiments  at  the 
University  of  Illinois  up  to  date  (1907)  is  6.13  per  cent,  and  the  highest  is  17.79. 


32  VARIATION 

many  score  cards  for  pure-bred  animals  !  Now  the  facts  are  that 
a  cow  is  kept  for  what  she  can  do,  and  there  is  nothing  inherent 
in  mere  color  that  is  indicative  of  her  ability  to  convert  feed  into 
either  milk  or  meat.  She  is  therefore  neither  better  nor  worse 
for  her  color  except  as  it  is  an  index  of  blood  lines  when  she  is 
to  be  used  as  a  breeder. 

So  striking  are  color  differences,  however,  and  so  distinct  are 
our  preferences,  that  we  instinctively  follow  our  prejudices  in  this 
respect,  quite  regardless  of  more  important  considerations,  until 
the  whole  fabric  of  breeding  is  interwoven  with  "fancy  points" 
in  the  shape  of  color  markings  that  greatly  confuse  the  breeder 
in  his  attempts  to  select  individuals  for  breeding  purposes. 

To-day  the  majority  of  prize-winning  shorthorns  are  either 
roan  or  pure  white.  Twenty-five  years  ago  no  breeder  would 
have  dared  to  show  a  roan  animal,  and  if  a  white  calf  had  been 
dropped  in  his  herd  he  would  have  destroyed  it  at  once  and  kept 
the  matter  as  secret  as  possible,  so  strong  was  the  red  color  craze 
following  the  American  worship  of  Bates  cattle.  This  craze, 
which  was  always  groundless,  cost  the  breed  and  their  admirers 
dearly  and  checked  by  a  decade  or  more  its  progress  upward. 

Probably  of  all  substantive  variations  color  is,  excepting  among 
flowers  and  ornamental  plants,  of  the  least  consequence  to  man ; 
yet  the  prejudice  is  with  us,  and  the  breeder  who  expects  to  sell 
his  product  must  reckon  with  it.  He  should  do  it  intelligently, 
however,  realizing  fully  that  individuals  vary  greatly  in  inherent 
quality  quite  independently  of  color. 

In  general  it  may  be  said  that  substantive  differences,  though 
not  so  easily  detected,  are  yet  of  far  more  significance  to  the 
farmer  than  are  those  of  either  form  or  size. 


CHAPTER  IV 

MERISTIC  VARIATION 

Meristic  variation  has  reference  to  a  deviation  in  the  number 
or  arrangement  of  repeated  parts  involved  in  the  plan  or  pattern 
upon  which  any  particular  organism  is  built. 

A  plant  or  an  animal  is  not  an  amorphous  lump  of  living 
matter.  On  the  contrary,  it  is  made  up  of  parts,  each  of  which  has 
a  kind  of  identity  of  its  own,  many  of  which  are  similar,  and  all 
of  which  are  definitely  related  and  placed  in  some  sort  of  orderly 
arrangement. 

Reflection  discloses  the  fact  that  each  organism  is  developed 
upon  a  specific  plan,  essentially  different  from  that  of  any  other, 
and  that  with  most  organisms  the  pattern  is  composed  of  a  defi- 
nite number  of  similar  parts  more  or  less  repeated. 

Thus  the  chicken  has  two  legs,  and  the  horse  has  four  legs, 
that  are  more  or  less  alike.  The  flower  has  many  petals,  the 
corn  plant  many  leaves ;  the  spinal  column  is  composed  of  vertebra 
very  much  alike,  and  organisms  generally  possess  many  parts 
that  more  or  less  closely  resemble  one  another. 

From  this  it  appears  that  the  individual  animal  or  plant  is 
not  a  unit  in  respect  to  form,  but  rather  that  it  is  made  up  of 
many  units,  some  of  which  are  practical  duplicates.  Thus  the 
idea  of  multiple  parts  in  orderly  arrangement  (merism)  comes  at 
once  into  the  study,  and  variation  in  the  number  or  character  of 
these  repeated  parts  (meristic  variation)  is  a  broad  and  compli- 
cated subject  affording  considerable  insight  into  the  nature  of 
variation.  Accordingly  it  is  profitable  to  pursue  it  at  considerable 
length,  not  so  much  for  the  material  involved,  which  consists 
largely  of  abnormalities  of  no  practical  interest  or  value,  but 
because  no  other  phase  of  variation  affords  so  much  information 
upon  the  real  nature  of  living  matter  and  its  adherence  to  or 
deviation  from  a  definite  plan. 

33 


34 


VARIATION 


SECTION  I— SYMMETRY 


The  central  thought  in  all  meristic  studies  is  symmetry,  by 
which  is  meant  that  opposite  sides  of  an  organism  possess  parts 
that  are  either  identical  or  at  least  similar.  Thus  the  petals  upon 
one  side  of  a  flower  are  in  most  cases  like  those  upon  the  oppo- 
site side,  and  the  blossom  is  made  up  of  a  number  of  similar  parts 
very  much  alike  and  several  times  repeated.1 

Among  higher  animals,  however,  opposite  sides  are  similar  but 
not  identical,  and  here  arises  the  distinction  between  radial  sym- 
metry and  bilateral  symmetry. 

Radial  symmetry  and  radial  series.  By  this  is  meant  that  kind 
of  pattern  in  which  the  separate  parts  are  identical  and  each  part 
is  capable  of  replacing  any  other  in  the  series.  Common  examples 
are  the  petals  of  most  flowers  (leguminous  and  the  like  excepted), 
the  leaves  and  lateral  shoots  of  plants,  the  capsules  of  many  seeds, 
such  as  the  apple,  orange,  etc.,  the  rows  of  corn  upon  the  cob, 
the  parts  of  the  sea  urchin,  the  starfish,  and  the  Radiolaria 
generally. 

In  all  cases  of  this  sort  the  individual  parts  could  each  replace 
any  other  part  of  the  series.  The  pattern  is  therefore  spoken  of 
as  one  of  radial  symmetry,  and  the  parts  as  members  of  a  radial 
series. 

Bilateral  symmetry.  Among  higher  animals  a  different  sym- 
metry is  observable.  While  each  side  has  its  counterpart  upon 
the  other,  yet  there  is  a  distinction  between  the  right  and  the 
left  sides  and  between  the  dorsal  and  the  ventral  surfaces.  In 
such  cases  the  parts  while  similar  are  not  alike,  nor  could  they 
replace  each  other. 

1  Symmetry  is  well-nigh  universal.  All  organisms  arise  through  cell  division  in 
one  or  more  planes,  and  some  degree  of  symmetry  is  to  be  expected  from  the 
manner  in  which  growth  takes  place. 

But  symmetry  is  not  confined  to  multicellular  structures.  Appendages  consist- 
ing of  single  cells  are  frequently  symmetrically  placed,  and  many  organisms,  which 
are  single  celled  and  therefore  microscopic,  as  diatoms,  secrete  a  skeleton  with 
regular  markings  as  symmetrical  as  hoarfrost  and  quite  as  beautiful. 

All  this  is  curious  rather  than  valuable  to  the  student  of  thremmatology  who 
is  interested  in  multicellular  beings ;  yet  it  all  throws  light  on  the  method  of  life, 
and  we  are  able  to  lay  down  the  principle  that  symmetry  is  not  only  the  natural 
corollary  of  development  by  cell  division,  but  that  it  is  also  a  general  principle  in 
living  matter. 


MERISTIC  VARIATION 


35 


The  right  hand  and  arm  are  made  upon  the  same  plan  as  the 
left,  but  could  not  replace  them  because  they  would  not  fit ;  the 
one  is  the  reverse  of  the  other. 

Reflected  in  the  mirror  the  right  hand  seems  to  be  the  left, 
but  it  is  an  illusion,  for  the  right  side  is  the  negative  or  optical 
image  of  the  left  with  all  its  elements  reversed.  Hence  a  part 
upon  the  one  side  could  not  replace  the  corresponding  part  upon 
the  other.  It  is  its  counterpart,  not  its  duplicate  as  among  leaves 
and  petals.  Thus  we  arrive  at  the  distinction  between  the  com- 
plexity of  bilateral  symmetry  and  the  simplicity  of  radial  symmetry. 
It  is  also  significant  that  bilateral  symmetry  is  characteristic  of 
higher  animal  life,  and  radial  symmetry  of  lower  animals  and  plants. 

Dorsal  and  ventral  surfaces.  The  fundamental  fact  at  the 
bottom  of  bilateral  symmetry  is  the  distinction  between  dorsal 
and  ventral  surfaces,  necessitating  differences  in  the  quadrants 
that  are  forced  to  work  in  opposition  to  each  other.1 

Indian  corn  and  the  grass  family  generally  are  as  distinctly 
bilateral  as  is  the  horse  or  man,  yet  there  is  no  thought  of  dorsal 
and  ventral  differences,  and  hence  no  distinction  between  right 
and  left. 

For  example,  let  the  leaves  of  a  corn  plant  and  the  arms  of  a 
man  extend  east  and  west.  Then  the  north  and  south  sides  of 
the  corn  plant  will  be  alike.  Not  so  with  the  man.  In  the  one 
direction  (we  will  say  the  south)  will  be  his  spinal  column  and 
the  general  framework  of  the  body  ;  in  the  other  (to  the  north) 
will  be  his  face,  his  nose,  his  eyes,  and  all  the  -active  external 
parts.  Moreover  his  hands  are  made  to  oppose  each  other  and  to 
work  together  with  this  (the  ventral)  side  of  the  body.  There  is 
therefore  bilateral  symmetry  in  one  direction  but  not  in  the  other. 

With  the  corn  plant  the  case  is  different.  It  does  not  move 
from  place  to  place,  and  it  presents  its  plain  sides  indifferently 
to  the  world.  Accordingly  no  distinctions  similar  to  dorsal  and 
ventral  are  possible.2 

1  The  word  "opposition  "  is  here  used  not  in  the  sense  of  "  antagonism  "  but 
as  "  placed  opposite  and  working  with  "  ;  as,  The  thumb  is  "  opposed  "  to  the 
other  members  of  the  hand,  thereby  making  a  working  unit. 

2  None  of  these  distinctions  should  be  confused  with  homologous  parts  or 
with  analogous  parts,  nor  should  the  ideas  be  confounded. 

Homologous  parts  belong  to  two  individuals,  not  one,  and  they  are  such  as 
bear  corresponding  structural  relations  to  their  respective  organisms,  suggesting 


36  VARIATION 

Bilateral  symmetry  not  complete.  Curiously  enough  not  all  the 
parts  follow  the  same  plan  as  to  bilateralism  and  symmetry.  What 
has  been  said  refers  to  paired  organs  standing  on  opposite  sides 
of  the  body,  as  hands,  arms,  legs,  eyes,  ears,  etc. 

Many  organs  not  paired  present  curious  facts  to  the  evolu- 
tionist. The  nose,  for  example,  has  no  counterpart,  but  it  stands 
on  the  median  line  and  has  a  bilateral  symmetry  of  its  own, 
being  made  up  of  right  and  left  halves.  The  liver  and  the  heart, 
however,  while  consisting  of  right  and  left  halves,  are  impaired 
organs,  placed  not  on  the  median  line,  but  the  one  upon  the  right, 
the  other  upon  the  left.  Each  has  a  bilateral  symmetry  of  its 
own,  with  distinct  right  and  left  sides,  yet  both  are  unsymmetric- 
ally  placed. 

The  stomach,  on  the  other  hand,  is  an  unpaired  organ  lying 
unsymmetrically  across  the  body,  and  its  own  bilateralism  is  not 
between  right  and  left  but  from  front  to  back.  The  kidneys  pre- 
sent the  anomalous  phenomena  of  paired  organs  with  a  bilateral- 
ism of  their  own  but  at  right  angles  to  that  of  the  body,  being 
also  from  front  to  back. 

Longitudinal  symmetry  and  linear  series.  Inasmuch  as  all 
growth  is  by  cell  division,  we  might  expect  longitudinal  symmetry 
as  well  as  lateral  symmetry.  Owing,  however,  to  the  definite 
relations  of  both  animals  and  plants  to  the  external  world,  it  is 
not  much  developed,  and  there  is  but  a  suggestion  of  longitudinal 
symmetry  to  be  found  in  either  plant  or  animal  forms. 

Most  plants,  are  both  geotropic  and  heliotropic  ;  that  is,  one 
part  goes  down  into  the  earth  in  response  to  gravity  and  the 
other  upward  toward  the  light  and  against  gravity.  This  makes 

common  descent.  Thus  the  leg  of  a  man  is  homologous  with  that  of  a  horse  or  a 
bird,  because  of  structural  resemblances.  In  the  same  sense  his  arm  is  homolo- 
gous with  the  fore  leg  of  the  horse  or  the  wing  of  a  bird. 

Analogous  parts  are  such  as  serve  the  same  purpose  in  different  organisms 
though  structurally  distinct.  Thus  the  flipper  of  the  whale,  which  is  a  modified 
hand,  is  analogous  to  the  fin  of  a  fish,  and  the  gill  of  a  fish  is  analogous  to  the 
lung  of  a  mammal,  because  it  serves  the  same  purpose,  though  there  is  no  struc- 
tural relation  between  the  two. 

The  homologue  or  the  analogue  of  a  part  is  therefore  to  be  found  in  another 
individual  and  of  a  different  species.  Symmetry,  on  the  contrary,  with  its  corollary 
of  multiple  parts,  refers  to  individuals  taken  singly  and  to  the  interrelations  of 
their  parts. 


MERISTIC  VARIATION  37 

the  two  extremities  at  once  very  different,  and  forestalls  the 
development  of  any  very  pronounced  symmetry  longitudinally. 

Animals  in  their  locomotion  establish  different  relations  at  their 
opposite  extremities,  thus  preventing  exact  symmetry  in  this  direc- 
tion, and  yet  reminders  of  inherent  tendencies  toward  universal 
symmetry  are  constantly  encountered.  Long  worms,  for  example, 
though  distinctly  different  at  the  extremities,  are  yet  composed 
of  rings  very  much  alike  throughout  most  of  their  length,  even 
permitting  locomotion  backward  with  considerable  facility. 

Longitudinal  division,  however,  with  or  without  corresponding 
symmetry,  is  everywhere  found  both  in  plant  and  animal  life,  espe- 
cially in  the  latter,  and  linear  series  of  similar  parts  present  as 
many  opportunities  for  variation  as  are  afforded  by  radial  series 
either  with  or  without  bilateral  symmetry.  Thus  the  rings  of 
worms,  the  vertebrae  and  the  ribs  of  the  body,  the  joints  of  the 
fingers  and  of  insect  parts,  —  all  these  are  fertile  sources  of 
meristic  variation. 

Homoeosis  in  meristic  variation.  This  is  a  form  of  variation  in 
which  one  part  assumes  the  characters  or  appearance  of  another, 
usually  quite  distinct.  It  is  a  frequent  accompaniment  of  meristic 
variations.  For  example,  an  extra  vertebra  may  be  found  in  the 
dorsal  series,  increasing  the  number  by  one,  —  all  normal.  This 
is  meristic  variation  of  the  simplest  kind,  with  no  homceosis. 

On  the  other  hand,  it  may  be  situated  at  the  front  of  the  dor- 
sal series  and  partake  somewhat  of  the  character  of  a  cervical 
(forward  homceosis),  or  it  may  be  located  at  the  rear  of  the  dor- 
sal series  and  in  many  respects  resemble  a  lumbar  (backward 
homceosis). 

This  posterior  dorsal  vertebra  may  bear  a  rib  that  is  bifurcated 
at  the  extremity,  one  branch  effecting  a  union  with  the  sacrum, 
the  other  floating,  in  which  case  there  is  doubt  as  to  the  real 
character  of  the  additional  vertebra,  whether  dorsal  or  lumbar. 

In  much  the  same  way  misplaced  organs  are  often  found.  A 
leaf  may  be  seen  growing  from  a  fruit,  an  antenna  may  spring 
from  an  injured  eye,  or  foot  appendages  may  develop  instead  of 
those  proper  to  the  extremity  of  the  antenna. 

All  cases  of  this  order,  in  which  one  organ  through  some  dis- 
turbance assumes  the  character  of  another  organ,  are  known  as 


38  VARIATION 

homceotic  variations,  and  homoeosis  of  some  sort  is  a  frequent 
accompaniment  of  meristic  variation  in  longitudinal  series.  The 
best  instance  of  this  is  found  in  the  petals  of  flowers  which  are 
recognized  by  botanists  as  modified  leaves,  and  instances  are  not 
rare  in  which  the  specimen  plainly  shows  the  various  transition 
states  from  leaf  to  sepal,  sepal  to  petal,  and  petal  to  stamen. 

This  tendency  of  one  part  to  assume  the  character  and  dis- 
charge the  functions  of  a  neighboring  part  is  an  important  phase 
of  variation,  throwing  much  light  upon  the  general  subject  of 
development. 

With  this  introduction  the  student  is  prepared  for  the  study  of 
meristic  variation  somewhat  in  detail,  in  which  he  will  find  that 
while  each  species  is  built  upon  its  own  somewhat  peculiar  and 
definite  pattern,  yet  this  pattern  is  subject  to  many  and  profound 
alterations,  and  the  organism  is  frequently  able  to  exist  upon  an- 
other and  much-distorted  plan,  all  of  which  goes  far  toward  enlight- 
ening the  student  as  to  the  variations  that  may  be  expected  in  the 
organic  world.  Studies  in  meristic  variation  are  useful  to  the  stu- 
dent of  thremmatology,  not  so  much  for  their  own  sake  as  for  the 
light  they  shed  upon  the  nature  and  manner  of  variation. 

Examples  of  meristic  variation.  Examples  of  meristic  varia- 
tion are  to  be  found  at  every  hand.  In  the  doubling  of  flowers 
and  the  stooling  of  grain,  in  increased  or  reduced  numbers  of 
fingers  and  toes,  in  the  four-leaved  clover  and  the  branching 
habit  of  many  plants,  —  everywhere  are  seen  alterations  in  the 
customary  plan  on  which  nature. does  its  work. 

Fortunately  an  extended  and  valuable  collection  of  meristic 
variations,  mostly  among  animals,  has  been  made  by  Bateson.1 
He  lists  his  data  under  886  headings,  each  recording  from  one 
to  several  authentic  cases. 

Equally  complete  data  covering  plants  have  not  been  collected, 
though  it  is  among  plants  that  meristic  variation  is  most  common. 
Indeed,  it  is  so  common  and  so  evident  that  formal  collection  is 
hardly  necessary.  The  student  is  therefore  referred  to  plant  life 
out  of  doors  and  to  Bateson's  collection  for  a  fuller  study  of  this 
important  subject,  a  bare  outline  of  which,  as  a  guide,  being  all 
that  is  attempted  here. 

1  Bateson,  Materials  for  the  Study  of  Variation  [Macmillan  &  Co.,  1894]. 


MERISTIC  VARIATION  39 

SECTION  II  — MERISTIC  VARIATION  IN   LINEAR  SERIES 

Vertebrae.  Among  fishes  and  snakes  variation  in  the  number 
of  vertebrae  may  be  very  great.  In  mammals  it  is  smaller  but 
yet  distinct,  as  in  the  following  examples,  instances  of  which, 
according  to  Bateson,  could  be  multiplied  indefinitely. 

ERINACEOUS  EUROP^EUS  (THE  HEDGEHOG)1 


No. 

Cervical 

Dorsal 

Lumbar 

Sacral 

Coccygeal 

TOTAL 

I 

7 

M 

6 

4 

II 

42 

2 

7 

15 

6 

3 

10  + 

3 

7 

16 

6 

3 

9  + 

4 

7 

'5 

6 

4 

12 

44 

5 

7 

15 

6 

4 

II 

43 

6 

7 

M 

6 

3 

9  + 

7 

7 

IS 

6 

3 

n  or  12 

8 

7 

15 

6 

3 

13 

44 

9 

7 

15 

6 

3 

12  or  13 

It  will  be  noticed  that  I  and  5  differ  only  in  the  dorsal  region, 
which  fact,  however,  affects  the  total,  but  that  4  and  8  differ  both 
in  the  sacral  and  the  coccygeal  without  affecting  the  total. 

Commenting  on  the  phenomena  of  an  additional  lumbar  or 
sacral  vertebra,  Bateson  says  : 

.  .  .  There  is  a  strong  suggestion  that  (in  cases  of  this  kind)  the  num- 
ber of  vertebrae  has  been  increased  by  simple  addition  of  a  new  segment 
behind,  after  the  fashion  of  a  growing  worm  ;  the  variation  of  vertebras 
thus  seems  a  simple  thing.  But  there  is  evidence  of  other  kinds,  which 
plainly  shows  this  view  of  the  matter  to  be  quite  inadequate. 

What  this  evidence  is  he  proceeds  to  show  by  succeeding 
examples,  a  few  of  which  are  reproduced  here  : 

In  a  skeleton  of  Pythott  tigris^  (No.  602,  Museum  of  the  College 
of  Surgeons]  the  vertebrae  are  normal  up  to  the  I47th  inclusive. 
The  1 48th  and  i4Qth  are,  however,  abnormally  short  from  front 
to  back,  suggesting  arrested  development  with  imperfect  separa- 
tion, although  each  vertebra  bears  a  normal  rib  on  either  side. 

1  Bateson,  Materials,  etc.,  p.  103.  2  Ibid.  pp.  103-105. 


40  VARIATION 

Passing  backward  in  the  same  specimen,  the  i66th  vertebra  is 
seen  to  be  normal  on  the  left  but  double  and  bearing  two  ribs  on 
the  right,  thus  greatly  crowding  the  ribs  on  that  side.  The  i85th 
vertebra  is  reported  in  the  same  condition,  both  being  doubled 
on  the  right  side  and  single  on  the  left  (see  Fig.  3). 

Following,  Bateson l  gives  two  examples  of  the  reverse  condi- 
tion, namely  with  duplicity  on  the  left  side,  and  another  with 

duplicity  on  the  right,  showing 
clearly  that  meristic  variation  in 
one  side  of  a  bilateral  symmetry 
may  or  may  not  involve  the  other 
side. 

Ribs.  Variation  in  the  dorsal 
region  necessarily  involves  the 
ribs.  Aside  from  this,  all  evi- 
dence goes  to  show  that  partial 
division  of  the  ribs  is  much  more 
common  than  is  variation  in  the 
number  of  vertebrae.  In  man, 
for  example,  the  cartilage  is  fre- 
quently divided  for  a  considerable 
distance  (1.5  in.)  back  from  the 

FIG.  3.  Meristic  variation  in  vertebrae:        sternum,   often   involving  a   real 
double  on  right  side.  —  After  Bateson    ,  _     ,          ..     .       ir 

bifurcation  of  the  rib  itself. 

Homceotic  variation  in  vertebrae  and  ribs.2  These  may  be  out- 
lined as  follows  (all  in  man,  except  as  noted) : 

I.  Cervical  resembling  dorsal:  backward  homceosis.  The  dis- 
tinguishing character  of  dorsal  vertebrae  is  the  bearing  of  ribs, 
but  this  character  is  often  assumed  by  neighboring  cervical, 
being  common  on  the  seventh  and  not  unknown  on  the  sixth. 
Of  fifty-seven  cases  examined  by  Struthers,  forty-two  showed 
ribs  on  both  sides  and  fifteen  on  one  side  only,  showing  a  tend- 
ency to  preservation  of  symmetry.  The  completeness  of  develop- 
ment ranges  all  the  way  from  the  merest  rudiments  (rare)  to  a 
perfect  rib  connected  by  cartilage  to  the  sternum  (also  rare),  the 
commonest  form  ending  free  or  being  joined  by  cartilage  to  the 
first  true  rib. 

1  Bateson,  Materials,  etc.,  p.  105.  2  Ibid.  pp.  106-128. 


MERISTIC  VARIATION  4! 

2.  Dorsal  resembling  cervical:   forward  homoeosis.    Not  so 
common  as  above,  but  Struthers1  describes  a  specimen  in  which 
the  first   pair  of  ribs   is  defective.     On   the   left   side   the   rib 
extends  but  two  fifths  of  the  way  around,  where  it  articulates 
with  a  process  on  the  second  rib.    On  the  right  side  it  joins  the 
second  rib  about  one  inch  beyond  the  tubercle.    As  seven  nor- 
mal cervical  vertebrae  are  present  in  this  specimen,  it  is  to  be 
regarded  as  a  modified  dorsal  rather  than  an  extra  cervical  assum- 
ing the  characters  of  the  dorsal,  as  in  the  preceding  cases. 

3.  Dorsal  resembling  lumbar.     Frequently    the    twelfth    rib 
in  man  is  rudimentary,  in  which  case  the  last  dorsal  vertebra 
assumes  the  form  and  general  appearance  of  a  lumbar. 

4.  Lumbar  resembling  dorsal.    Cases  of  a  thirteenth  rib  are 
not    unknown    but    are    more  rare    than   the  reduction  of  the 
twelfth. 

5.  Homceosis  between  lumbar,  sacral,  and  coccygeal.    The  last 
lumbar  may  unite  on  one  or  both  sides  with  the  sacral,  in  which 
case  the  lumbar  develops  processes  to  assist  in  the  support  of 
the  ilium.    On  the  contrary,  the  first  sacral  may  remain  detached, 
thus  becoming  practically  a  lumbar.    Similar  relations  obtain  be- 
tween the  sacral  and  the  coccygeal. 

A  careful  study  of  this  whole  subject  develops  the  following 
facts : 

1.  That  an  increase  in  the  number  of  parts  in  one  region  may 
or  may  not  affect  the  total  number  in  the  series. 

2.  That  consequently  a  change  in  number  in  one  region  may 
or  may  not  be  accompanied  by  changes  in  other  regions  of  the 
same  series  ;  that  is,  changes  in  the  dorsal  do  not  imply  changes 
in  either  the  cervical  or  the  lumbar. 

3.  That  homoeosis  in  vertebrae  and  ribs  is  confined  to  members 
contiguous  ;  that  is,  if  a  cervical  resemble  a  dorsal,  it  will  be  that 
cervical  lying  next  to  the  dorsal  series. 

4.  That  the  tendency   is  for  an  extra  member  to  resemble 
somewhat  the  members  of  the  next  region  ;  that  is,  an  extra 
dorsal   is   likely   to  resemble  a  lumbar  or  a  cervical,  if  not  to 
entirely  replace  it,  suggesting  that  it  arose  at  the  end,  and  not 
in  the  middle,  of  the  dorsal  series. 

1  Bateson.  Materials,  etc.,  p.  109. 


42  VARIATION 

5.  That  forward  homoeosis  in  one  region  is  not  necessarily 
attended  by  forward  homoeosis   in  other  regions  of   the  same 
series. 

6.  That  in  general  (especially  in  man,  where  this  has  been 
most  studied)  forward  homoeosis  is  attended  by  a  total  increase 
of  the  series,  and  backward  homoeosis  by  a  decrease. 

7.  That  an  abnormality  on  one   side   may  or    may  not   be 
attended  by  a  like  abnormality  on  the  other,  though  the  tend- 
ency is  strongly  to  the  preservation  of  bilateral  symmetry. 

8.  That  when  one  part  resembles  another  it  is  the  member 
lying  contiguous ;  that  is,  a  dorsal  vertebra  will  resemble  a  cer- 
vical or  a  lumbar,  not  a  sacral,  and  lying  between  the  stamen 
and  the  leaf  are  the  petal  and  sepal  and  all  intermediate  grada- 
tions, either  present  or  obliterated. 

Meristic  variation  in  spinal  nerves.  Branches  from  the  spinal 
cord  emerge  between  the  vertebrae,  so  that  in  general  the  sys- 
tem of  spinal  nerves  is  determined  by  the  vertebrae.  Aside  from 
this,  however,  the  emergence  of  the  branches  varies  greatly 
both  in  number  and  in  conformation,  even  when  the  vertebrae 
are  normal. 

Fiirbringer's1  studies  in  birds  show  that  the  minimum  num- 
ber of  spinal  nerves  forming  the  brachial  plexus  (supplying  the 
wings)  is  three,  but  in  some  species  it  rises  as  high  as  six. 
Moreover,  in  some  instances  the  number  varied  from  four  to 
five  within  a  single  species,  and  in  one  (the  pigeon)  the  varia- 
tion was  from  four  to  six.  As  might  be  suspected,  the  two  sides 
are  often  differently  supplied.  For  example,  in  one  specimen 
(goose)  "  the  plexus  was  formed  on  the  right  side  by  nerves  xvi, 
xvn,  xvm,  and  xix,  while  on  the  left  side  it  received  a  strand 
from  the  xxth  nerve  in  addition  to  these." 

Fiirbringer's  tables  show  that  in  some  specimens  of  the  goose 
the  wings  were  supplied  by  the  nerves  xv  to  xix,  while  in 
others  they  were  supplied  by  the  xvnth  to  the  xxth.  In  the 
dove  the  brachial  plexus  was  formed  by  the  xth  branches  of 
the  spinal  nerve  in  some  specimens,  by  the  xnth  to  the  xvth 
in  others,  and  in  one  case  by  the  xith  to  the  xivth  as  an 
intermediary. 

1  Bateson,  Materials,  etc.,  pp.  129-135. 


MERISTIC   VARIATION 


43 


Herringham *  dissected  to  their  origin  the  nerves  forming 
the  brachial  plexus  in  fifty-five  human  subjects  (thirty-two  fetal 
and  twenty-three  adult).  Quoting  from  his  work,  Bateson  says  : 

The  origin  of  the  ulnar  nerve  was  traced  in  thirty-two  cases,  fourteen 
being  adults.  It  (the  ulnar  nerve)  was  found  to  arise  in  four  different  ways. 
Most  commonly  it  arises  from  the  vinth  and  ixth ;  this  occurred  in  twenty- 
three  cases.  With  the  vinth  and  ixth  is  sometimes  combined  a  strand  from 
the  vnth,  as  shown  in  five  cases  (four  fetal,  one  adult).  In  three  fetal 
cases  it  arose  from  the  vnith  only,  and  in  one  fetal  and  one  adult  case  from 
the  vuth  and  vinth.  ...  In  several  cases  the  branch  from  the  vnith  was 
much  larger  than  that  from  the  ixth,  but  the  reverse  was  never  met  with. 

Similar  conditions  were  found  elsewhere  with  man,  the  gorilla, 
baboon,  and  chimpanzee,  and  the  following  principle  was  set 
forth:  "  Any  given  fiber  may  alter  its  position  relative  to  the 
vertebral  column,  but  will  maintain  its 
position  relative  to  other  fibers.''' 

Homceosis  in  insects  and  other  small 
animals.  The  replacement  of  one  part 
by  another,  while  common  among  plants 
(modified  leaves  and  stems),  is  compar- 
atively rare  in  animal  life.  It  is,  however, 
by  no  means  unknown,  and  some  striking 
examples  are  quoted  from  Bateson  to 
show  the  remarkable  manner  in  which  a 
perfect  part  may  arise  in  a  most  unusual  FlG-  4-  Homceotic variation 


place,  among  which  are  the  following  :2 


in  sawfly:  right  antenna 
normal;  left  antenna 
bearing  a  foot.  A  and  B, 
enlarged. — After  Bateson 


1.  Specimens  of  sawfly  (Cimbex  axillaris}  in 
which  the  left  antenna  ended  in  "  a  well-formed 

foot,  having  a  pair  of  normal    claws   and  the  plantula   between  them " 
(Fig.  4).    Right  antenna  normal.3 

2.  A  male  bumblebee  {Bombus  variabilis}  taken  in  Munich  showed  the 
left  antenna  "  partially  developed  as  a  foot,"  bearing  "  a  pair  of  regularly 
formed  claws  like  the  claws  of  the  foot." 

3.  A  male  specimen  viZygana  filipendulce  "  possessing  a  supernumerary 
wing  arising  in  such  a  position  as  to  suggest  that  it  replaced  a  leg"  (Fig.  5). 
The  extra  wing  was  on  the  left  side  and  projected  from  the  underside  of  the 
body  after  the  exact  fashion  of  the  leg,  which  was  absent.    The  specimen 

1  Bateson,  Materials,  etc.,  pp.  135-138.  2  Ibid.  p.  147. 

3  Ibid.  pp.  146-155.     Professor  Bateson  vouches  for  the  genuineness  of  this 
specimen,  which  he  himself  carefully  examined,  although  it  belonged  to  Dr.  Kraatz. 


44 


VARIATION 


belongs  to  Mr.  Richardson,  and  was  examined  by  Professor  Bateson  as 
closely  as  was  possible  without  removing  the  hairs,  to  which  the  owner 
objected.  It  is  well  known  that  supernumerary  wings  may  arise  with  the 
normal  number  of  legs.  In  this  case  the  closest  examination  failed  to  reveal 

even  a  rudimentary  leg,  and  there  was  cer- 
tainly "  no  empty  socket  or  other  suggestion 
that  the  rest  of  the  leg  had  been  lost." 

4.  Specimen  of  Palinurus penicillatus  with 
an  "  antenna-like  flagellum  growing  up  from 
the  surface  of  the  (left)  eye." 

5.  The  female  crayfish  has  normally  a  pair 
of  oviducal  openings  on  the  bases  of  the  ante- 
penultimate pair  of  walking  legs.    This  speci- 
men possessed  in  addition  a  pair  also  on  the 

p— -- showing  irreg?ar  sf^entatir, 

6.  Another  specimen,  also  of  the  crayfish, 
possesses  an  extra  pair  of  oviducal  openings,  as  in  the  last,  except  that  they 
were  placed  on  the  last  pair  of  legs,  skipping  the  penultimate.    It  is  note- 
worthy that  this  is  the  normal  position  for  the  sexual  organs  of  the  male, 
except  that  the  openings  were  placed  in  their  own  proper  position  on  the  leg 
and  not  "  at  the  posterior  surface  of  the  joint  as  the  male  openings  are." 

7.  Bateson  himself  examined   586  female  crayfish  for  abnormalities  of 
oviducal  openings.    Of  this  number  he  found  563   were  normal   and  23 
abnormal,  as  follows : 

1.  Extra  oviducal  opening  on  left  penultimate  leg 7 

2.  Extra  oviducal  opening  on  right  penultimate  leg       .     .     .     .  10 

3.  Extra  oviducal  opening  on  both  penultimate  legs     ....  i 

4.  Extra  oviducal  opening  on  both  penultimate  and  last  legs      .  i 

5.  Single  oviducal  opening  on  left  side  only 3 

6.  Single  oviducal  opening  on  right  side  only i 

Total  abnormal  specimens  23 

Bateson  reports  but  one  abnormal  specimen  out  of  7 1 4  males  examined 
by  him,  and  this  abnormality  consisted  in  the  absence  of  a  generative  open- 
ing on  the  right  side. 

8.  Among  earthworms  will  be  found  many  cases  of  imperfect  segmenta- 
tion, showing  more  rings  on  one  side  than  upon  the  other,  often  suggesting 
a  spiral  rather  than  a  series  of  rings.    Great  irregularity  is  also  found  in  the 
position  of  generative  openings,  as  to  whether  paired  or  single,1  although 
the  male  parts  are  always  posterior  to  the  female,  whatever  the  number  of 
the  ring  on  which  either  is  borne. 

Cervical  fistulae  and  auricular  appendages  in  mammals.2 
Cervical  fistulae  are  openings  in  the  neck,  occurring  singly  or  in 
pairs  and  located  anywhere  from  the  median  line  backward  as 

1  Bateson,  Materials,  etc.,  pp.  156-166.  *  I  hid.  pp.  174-180. 


M ERISTIC   VARIATION 


45 


far  as  the  angle  of  the  jaw.  The  opening  is  sometimes  slight, 
but  often  it  extends  completely  to  the  pharynx.  In  the  latter 
case  it  is  possible  to  pass  an  instrument  the  size  of  a  small 
quill,  provided  the  opening  is  comparatively  straight,  otherwise 
its  completeness  or  incompleteness  may  be  ascertained  by  the 
injection  of  a  liquid. 

Bateson  quotes  Fisher1  as  describing  sixty-five  persons  with 
seventy-nine  fistulae.    Fourteen  of  these  were  bilateral  (occurring 


"x 


FIG.  6.  Child  with  supernumerary  auricle  on  each  side  of  the  neck.  —  After 
Bateson,  from  Birkett 

on  both  sides),  and  fifty -one  were  unilateral,  of  which  thirty- 
three  were  on  the  right  side.  He  adds,  "  There  was  evidence  of 
heredity  in  twenty-one  cases." 

Auricular  appendages,  often  called  supernumerary  auricles, 
are  not  at  all  uncommon.  They  are  non-functional  growths 
occurring  in  the  neighborhood  of  the  ear  but  below  it,  and  are 
generally  accompanied  by  some  deformity  of  that  organ.  They 
consist  of  little  flaps  of  skin  or,  more  commonly,  of  cartilaginous 
growths  identical  in  texture  with  that  of  the  normal  external  ear. 

1  Bateson,  Materials,  etc.,  p.  175.  Obvious  errors  in  figures  prevent  further 
quotations  that  would  otherwise  be  of  interest. 


46  VARIATION 

One  of  the  most  remarkable  cases  ever  described  is  that  of 
an  infant  brought  to  Guy's  hospital  in  iSsi.1  Ano'ther  was 
of  a  child  having  a  well-developed  supernumerary  auricle  on 
each  side  of  the  neck  (see  Fig.  6).  These  appendages  were 
easily  removed  and  proved  to  be  entirely  cutaneous,  though 
each  was  served  by  a  small  artery. 

Whether  cervical  fistulae  are  to  be  regarded  as  remains  of 
unclosed  gill  slits,  or  whether  they  are  to  be  regarded  as  repeti- 
tions of  the  external  ear,  in  any  event  their  presence  shows  a 
pronounced  tendency  to  repeat  certain  characteristic  structures 
in  this  particular  region  of  the  body. 

Growths  of  this  character  are  by  no  means  confined  to  man. 
Cervical  auricles  (the  so-called  "  wattles  ")  are  common  in  sheep, 
especially  merinos.  They  are  well  known  in  goats  and  are  ex- 
ceedingly common  in  many  strains  of  unimproved  swine.  Strange 
as  it  may  seem,  these  repetitions  of  the  ear  appendages  are  un- 
known in  either  the  horse  or  the  ox. 

Meristic  repetition  in  mammae.2  One  of  the  chief  distinguish- 
ing features  of  mammals  is  milk  secretion.  Speaking  generally, 
this  occurs  at  some  point  or  points  on  either  side  of  the  ventral 
surface  of  the  body  on  lines  running  from  the  armpit  to  the 
groin.  In  swine  and  in  dogs  it  is  distributed  throughout  the 
entire  extent  of  these  mammary  lines.  In  cattle,  horses,  goats, 
sheep,  etc.,  it  is  confined  to  the  rear  extremity  of  the  line,  and 
in  the  elephant  it  is  as  decidedly  forward,  the  udder  being  located 
at  the  armpit.  In  the  human  being  the  point  of  normal  activity 
is  relatively  further  back  (down)  than  in  the  elephant,  but  yet 
above  the  middle. 

This  latter  point  is  established  by  the  fact  that  supernumerary 
nipples  are  found  both  above  and  below  the  normal.  The  fact 
that  no  less  than  three  supernumeraries  have  been  found  above 
indicates  that  the  normal  mammae  are  perhaps  fourth  in  a  full 
series.  It  is  to  be  noted  in  this  connection,  however,  that  in 
most  cases  supernumeraries  are  situated  below  rather  than  above 
the  normal.  These  structures  vary  all  the  way  from  mere  nipples 
resembling  warts  and  entirely  unaccompanied  by  mammary  tissue 

1  Bateson,  Materials,  etc.,  p.  178.  2  Ibid.  pp.  181-195. 


MERISTIC  VARIATION  47 

up  to  well-formed  organs  fully  functional.  Curiously  enough  super- 
numerary mammae  are  more  common  in  men  than  in  women. 

Bateson l  quotes  Bruce  as  having  found  in  2  3 1 1  females  fourteen 
cases  (0.605  percent),  and  in  1645  males  forty-seven  cases  (2.857 
per  cent).  In  another  series  315  subjects  were  examined,  show- 
ing twenty-four  cases  (7.6  per  cent),  nineteen  being  male  and 
five  female.  Bardeleben  is  also  quoted  as  having  examined  2736 
recruits  (all  males,  of  course).  In  this  series  "637  cases  (23.3 
per  cent)  were  seen,  2 1 9  being  on  the  right  side,  248  on  the  left, 
and  170  on  both  sides." 

The  largest  number  of  supernumerary  mammae  ever  recorded 
was  in  a  subject  described  by  Neugebauer.2  This  patient  had 
five  pairs  of  nipples,  of  which  the  fourth,  numbered  from  above, 
was  the  normal.  When  the  child  was  being  suckled  milk  oozed 
from  each  of  the  uppermost  pair,  but  all  other  supernumeraries 
yielded  milk  only  with  pressure. 

Extra  teats  in  cows  are  too  common  to  need  mention  except  to 
call  attention  to  their  excessive  number.  The  cow  Rose,  famous 
for  her  record  at  the  Illinois  Station,3  had  in  all  eight  mammae, 
six  of  which  were  fairly  well  developed,  though  only  four  were 
functional.4  It  is  noticeable  that  supernumeraries  are  nearly 
always  posterior  to  the  normal  or  else  constitute  a  doubling  of  one 
of  the  normals.  Every  milker  knows  by  sad  experience  that  these 
supernumeraries  are  not  only  common  but  frequently  functional. 

A  close  study  of  this  subject  shows  that  repetition  of  these 
parts  may  be  by  pairs  or  singly ;  that  the  repeated  parts  may  be 
on  the  same  or  on  different  levels  ;  that  they  may  be  out  of  line, 
being  in  some  cases  very  near  the  median,  and  that  the  normal 
nipple  may  be  doubled.  From  the  latter  fact  we  further  establish 
the  point  that  meristic  variation  may  occur  in  two  ways,  —  either 
by  addition  to  the  series  or  by  division  of  a  normal  number.  We 
shall  find  the  same  in  teeth. 

1  Bateson,  Materials,  etc.,  pp.  182-183. 

2  Ibid.  p.  183. 

3  See  Bulletin  No.  66. 

4  These  supernumeraries  were  not  symmetrically  placed.    On  the  right  side  the 
two  extra  teats  were  placed  behind  the  two  functional,  as  is  commonly  the  case  ; 
but  on  the  left  side  only  one  supernumerary  was  so  placed,  while  the  other  was 
between  the  two  functional  teats. 


48  VARIATION 

Meristic  variation  in  teeth.  As  Bateson  remarks,  "Teeth 
arise  by  special  differentiation  at  points  along  the  jaw,  as  mammae 
arise  by  special  differentiation  at  points  along  the  mammary  line," 
and  we  shall  see  that  with  teeth  as  with  mammae  these  points 
of  special  differentiation  may  frequently  lie  outside  the  normal 
region,  that  they  are  subject  to  increase  or  decrease  in  number, 
and  that  the  increase  may  be  due  either  to  the  addition  of  a  mem- 
ber to  the  series,  to  the  interpolation  of  a  member,  or  to  the 
division  of  a  normal  member. 

Before  considering  special  cases  it  is  well  to  note  that  the 
similarity  between  the  right  and  left  jaws  is  that  of  ordinary 
bilateral  symmetry,  but  that  there  is  also  a  kind  of  symmetry, 
not  very  close  but  still  marked,  between  the  dentition  of  the 
upper  and  that  of  the  lower  jaw.  It  should  be  further  noted 
that  in  many  animals,  as  in  the  shark,  alligator,  etc.,  the  denti- 
tion constitutes  a  series  in  which  the  separate  teeth  differ  from 
one  another  mainly  in  size.  But  mammals  for  the  most  part  are 
heterodont ;  that  is,  the  series  is  broken  up  into  groups  which 
differ  among  themselves,  though  the  members  of  the  separate 
groups  resemble  one  another  closely.  Thus  the  incisors  are 
quite  different  from  the  canines,  which  in  turn  differ  from  the 
premolars  and  the  molars.  The  different  incisors,  however, 
are  very  much  alike,  and  the  same  is  true  of  the  canines  and  the 
various  molars  and  premolars.  Meristic  variation  in  a  heteroge- 
nous  series  like  this  is  manifestly  much  more  complicated  than 
in  a  simple  series  like  the  mammae  or  the  rii>s.  With  this  intro- 
duction attention  will  be  called  to  a  few  special  examples  quoted 
from  the  237  cases  that  have  been  collected  by  Bateson.1 

1.  One  hundred  and  fifty-two  adult  skulls  of  anthropoid  apes  showed 
twelve  cases  of  extra  teeth.    One  was  an  incisor,  one  was  anomalous,  and  the 
others  were  molars.    This  is  nearly   8  per  cent  abnormal,  as  against  425 
Old  World  monkeys  that  showed  but  two  cases  of  extra  teeth,  —less  than 
one  half  of  I  per  cent. 

2.  Adult  orang,  with  an  additional  posterior  molar  on  both  sides  above 
and  on  the  left  side  below.    No  trace  of  extra  molar  on  right  side  was  dis- 
covered, "  though  there  is  almost  as  much  room  for  it  as  on  the  left  side." 
Extra  molars  perfect  but  slightly  smaller  than  the  normal. 

1  Bateson,  Materials,  etc.,  pp.  195-273. 


MERISTIC  VARIATION 


49 


3.  Skull  (orang)  No.  2043 a,  Oxford  Museum,  is  normal  except  as  to  the 
second  premolar  in  the  upper  jaw  (j&2).    Both  these  teeth  are  missing  from 
their  proper  place.    There  is  plenty  of  space  on  the  left  side  but  somewhat 
less  than  the  normal  on  the  right  side.    The  missing  tooth  of  the  right  side 
is  present  in  the  skull,  but  instead  of  being  in  its  proper  place  it  stands  up 
from  the  roof  of  the  mouth  within  the  arcade  immediately  in  front  of  the 
right  canine  and  almost  exactly  on  the  level  of  the  second  incisor,  being  in 
the  premaxilla  at  some  distance  in  front  of  the  maxillary  suture. 

Discussing  this  case,  Bateson  observes  : 

That  this  tooth  is  actually  the  second  premolar  which  has  by  some  means 
been  shifted  into  this  position  there  can  be  no  doubt  whatever.  It  has  the 
exact  form  of  the  second  premolar  and  is  of  full  size.  It  stands  nearly  verti- 
cally, but  is  a  little  inclined  towards  the  outside.  The  canine  is,  by  the 
growth  of  this  tooth,  slightly  separated  from  the  second  incisor,  and  the  first 
premolar  is  consequently  pushed  also  somewhat  further  back.  Hence  it 
happens  that  the  diastema  space  for  the  second  premolar  on  the  right  side 
is  not  of  full  size.  This  should  be  understood,  as  it  might  otherwise  be 
imagined  that  the  contraction  was  due  to  a  complementary  increase  in  the 
size  of  the  other  teeth,  of  which  there  is  no  evidence. 

The  missing  premolar  on  the  left  side  was  not  visible,  but  "  on 
the  left  side  of  the  palate  there  was  a  very  slight  elevation  at  a 
point  homologous  and  symmetrical  with  that  at  which  the  second 
premolar  on  the  right  side  was  placed.  ...  A  small  piece  of 
bone  was  here  cut  away,  with  the  result  that  a  tooth  of  about  the 
same  size  and  formation  as  /2  was  found  imbedded  in  the  bone." 
In  this  case,  therefore,  the  upper  premolars  on  both  sides  had 
"  traveled  away  from  their  proper  positions  and  taken  up  new 
and  symmetrical  positions  in  the  palate,  anterior  to  the  canines." 

As  Bateson  pertinently  remarks  (italics  and  parenthesis  mine), 
"  The  facts  of  this  case  go  to  show  that  the  germ  of  a  tooth  con- 
tains within  itself  all  the  elements  necessary  to  its  development  in 
its  ozvn  true  form  [even  in  an  abnormal  position],  provided  of 
course  that  nutrition  is  unrestricted."  This  is  a  significant  point 
of  peculiar  interest  to  students  of  thremmatology,  not  because  of 
its  bearing  upon  dentition  but  because  of  the  light  it  affords  upon 
the  basis  of  variability  and  the  ultimate  units  of  variation. 

4.  Gorilla  from  the  Congo,  with  a  fifth  incisor  standing  almost  in  the 
middle  of  the  lower  jaw.    It  has  the  characteristic  chisel  shape  of  the  incisor, 
but  it  is  «  turned  half  round  so  that  the  plane  of  its  chisel  stands  obliquely." 


50  VARIATION 

5.  Dog  with  lower  jaw  and  teeth  normal,  but  with  upper  canines  imper- 
fectly divided.    The  division  was  more  complete  on  the  right  side,  forming 
practically  two  canines  standing  in  line  with  the  regular  teeth. 

6.  Dog  with  first  premolar  in  right  side  of  upper  jaw  doubled,  both  teeth 
being  normal  in  shape,  the  anterior  somewhat  the  larger. 


FIG.  7.    Merism  in  teeth  :  canines  partially  divided.  —  After  Bateson 

7.  Dog  with  an  extra  premolar  on  both  sides  above  and  below,  the  denti- 
tion formula  being  p     ~~     . 

8.  Sledge  dog :  "  All  teeth  normal,  except  left  upper  p  2.    This  tooth  nor- 
mally has  two  roots.    Here  it  is  represented  by  two  teeth,  each  having  one 
root." 

9.  Absence  of  first  premolar  frequently  quite  common  in  Eskimo  dogs, 
suggesting  a  breed  peculiarity. 

10.  Among  domestic  dogs  supernumerary  molars  were  found  in  twenty- 
eight  cases  out  of  345  skulls  examined,  as  follows,1  the  normal  dentition  of 
the  dog  as  to  molars  being  two  above  and  three  below  (m  2). 

tn9  on  both  sides  and  m*  on  one  side I  case 

m*  on  both  sides 2  cases 

#z8  on  one  side 9  cases 

w8  and  w4  on  one  side  only 2  cases 

m4  on  both  sides 6  cases 

m*  on  one  side  only 8  cases 

This  strongly  suggests  the  formula  wf,  which  is  that  of 
Otocyon  (Lalandes  dog)  and  of  the  fossil  Amphicyon,  the  sup- 
posed doglike  progenitor  of  the  bears.  It  calls  to  mind  the 
further  remarkable  facts  that  Otocyon  itself  varies  from  m\ 
to  m  |  and  that  it  is  the  only  mammal  outside  the  marsupials 

1  Bateson,  Materials,  etc.,  p.  220. 


MERISTIC  VARIATION  51 

that  ever  has  four  molars  on  both  jaws,1  which  goes  far  to  indi- 
cate a  marsupial  ancestry. 

Remembering  that  the  teeth  are  considered  as  one  of  the  few 
most  reliable  bases  for  classification,  the  remarkable  variation  in 
their  number,  character,  and  position  throws  no  little  light  on 
the  manner  in  which  variation  behaves,  which  is  the  chief  reason 
for  their  extended  notice  here. 

Supernumerary  eyes.  The  development  of  extra  eyes  seems 
to  be  confined  to  insects,  which  afford  a  number  of  excellent 
examples  of  the  development  of  normal  tissue  in  abnormal 
situations. 

Bateson's  Nos.  419  to  421  are  all  cases  of  the  development 
of  a  third  eye  in  Coleoptera.  In  every  case  these  extra  eyes  are 
quite  distinct  from  the  normal.  In  No.  419  the  supernumerary 
was  small  and  lay  abutting  against  but  distinct  from  the  right 
eye.  Its  color  was  brownish  yellow,  while  the  normal  eye  was 
black.  In  No.  420  the  extra  eye  was  on  the  left  side  but  quite 
independent  of  the  normal  eyes,  which  were  exactly  alike.  In 
No.  421  the  extra  eye  was  on  the  left  side  of  the  head,  which 
was  rather  less  developed  than  the  right.  This  eye  is  borne 
upon  an  irregular  chitinous  loop,  having  a  diameter  of  about 
2.5  mm.  This  loop  is  attached  to  the  substance  of  the  head 
before  and  behind,  and  these  two  attachments  are  distant  from 
each  other  about  i  mm.  The  diameter  of  the  eye  is  about  2.5  mm., 
thus  occupying  the  full  surface  of  the"  loop,  and  its  faceting  is 
said  to  be  "not  quite  regular,  and  finer  and  slighter  than  that  of 
the  normal  eye."  It  is  thus  a  very  good  attempt  at  a  functional 
third  eye. 

Supernumerary  wings  in  insects.  Bateson2  reports  and  de4 
scribes  fifteen  cases  of  extra  wings  among  insects,  —  sometimes 
on  one  side,  sometimes  on  the  other,  but  generally  if  not  always 
smaller  than  the  normal  ;  sometimes  plainly  identified  with  the 
fore  wing,  more  frequently  with  the  posterior ;  occasionally  nor- 
mal in  coloring  and  scaling,  but  as  a  rule  abnormal.  In  one  in- 
stance it  took  the  form  of  a  large  upright  scale  and  in  another  of 
a  winglike  appendage  to  the  left  anterior  wing. 

1  Lydekker,  Library  of  Natural  History,  p.  580. 

2  Bateson,  Materials,  etc.,  pp.  281-285. 


VARIATION 

Meristic  variation  in  horns.1  These  appendages  afford  good 
material  for  studies  in  variation.  They  sometimes  consist  of 
horny  matter  (cattle,  sheep,  rhinoceros,  etc.)  and  sometimes  of 
true  bone,  as  in  the  deer.  They  sometimes  persist  through  life 
(cattle,  sheep,  goats,  etc.)  and  sometimes  are  periodically  shed, 
as  with  the  antlers  of  the  stag.  They  sometimes,  as  in  cattle, 
have  a  bony  case,  which  is  a  true  outgrowth  of  the  skull,  but 
often,  as  in  the  rhinoceros,  they  have  no  connection  whatever 
with  the  bone  beneath.  Again,  the  antlers,  which  are  bony,  sep- 
arate with  a  clean  scar  from  the  bone  of  the  skull,  as  a  leaf 
stem  parts  from  its  twig. 

The  meristic  variations  of  horns  are  no  less  remarkable  than 
their  substantive  variations  just  mentioned.  They  are  for  the 
most  part  symmetrically  placed  in  pairs  on  either  side  of  the 
skull  just  above  the  eyes,  though  the  horn  of  the  rhinoceros  is 
borne  upon  the  nose  and  therefore  upon  the  median  line. 

Variation  in  number  occurs  either  symmetrically  or  asymmet- 
rically. If  the  rhinoceros  has  an  extra  horn  it  will  be  just 
above  and  on  the  median  line  with  the  normal.  Sheep  may  have 
an  extra  pair  just  external  to  (behind)  the  normal,2  or  there  may 
be  three  on  one  side  and  two  on  the  other.  In  the  latter  case  the 
third  horn  will  be  a  little  one  lying  between  the  normal  and  the 
more  ordinary  extra  horn.  In  still  other  cases,  according  to 
Bateson,  a  double  core  will  be  found  incased  in  a  kind  of 
"double-barreled"  single  horn. 

Among  cattle  no  increase  in  the  normal  number  of  horns  is 
known  to  the  writer,  but  their  entire  absence  is  common. 
Indeed,  the  readiness  with  which  the  polled  character  appears  is 
astonishing,3  particularly  as  it  is  associated  with  a  peculiar  prom- 
inence (the  poll)  lying  between  and  often  slightly  below  the 
normal  base  of  the  horns.  In  cattle,  meristic  variation  in  horns 
seems  to  be  associated  neither  with  divided  horns  or  extra 
prongs. 

1  Bateson,  Materials,  etc.,  pp.  285-287. 

2  Four-horned  breeds  are  not  unknown.    Bateson,  Materials,  etc.,  p.  285. 

8  It  is  a  well-known  fact  that  if  either  parent  be  polled  the  horns  are  almost 
certain  to  be  absent  in  the  offspring,  and  Storer,  in  his  Wild  White  Cattle  of 
Great  Britain,  says  there  is  evidence  that  these  park  cattle  have  been  several 
times  alternately  polled  and  horned  since  their  inclosure  in  the  parks. 


MERISTIC   VARIATION 


53 


Besides  sheep  Bateson  gives  three  specific  cases  of  increase  in 
the  number  of  horns,  as  follows:  (i)  a  family  of  goats  in  which 
the  four-horned  character  was  hereditary  for  "  many  genera- 
tions "  ;  (2)  chamois  with  two  "  well-formed  and  sym- 
metrical extra  horns  "  ;  (3)  roebuck,  two  specimens  of 
which  are  figured.  Of  these  one  has  two  horns  on  one 


FIG.  8.   Abnormal  horns  in  roebuck :  all  but  one  have  undergone  meristic 
variation.  —  After  Bateson 

side  and  three  on  the  opposite  side,  while  the  other  has  three  on 
one  side,  the  other  being  normal,  consisting  of  a  single  horn 
with  one  prong  near  the  summit  (see  Fig.  8). 

Meristic  variation  in  digits.1  Variations  in  these  parts  are 
peculiarly  complex.  There  may  be  an  increase  or  a  decrease 
not  only  in  the  total  number  but  also  in  the  parts  or  joints  that 
compose  the  several  members. 

The  best  example  covering  both  these  points  in  the  same 
individual  is  Bateson's  No.  485.2  In  this  case  the  right  hand 


1  Bateson,  Materials,  etc.,  pp.  311-410. 


2  Ibid.  p.  327. 


54 


VARIATION 


has  the  usual  number  of  digits,  but  the  thumb  has  three  instead 
of  two  phalanges,  though  its  general  shape  is  normal.  In  the 
left  hand  there  is  much  confusion  in  the  region  of  the  thumb. 
There  is  an  extra  digit,  but  its  true  character  is  not  so  evident. 
It  is  sharp,  like  a  finger,  but  functions  as  a  thumb.  Internal  to 
this  is  a  thumblike  supernumerary  with  a  true  nail,  but  from 
its  position  it  is  functionless  (see  Fig.  9). 


FIG.  9.  Meristic  variation  in  the  hand :  right  and  left  hands  of  the  same  indi- 
vidual, showing  on  the  left  hand  a  duplication  of  the  forefinger  at  the 
expense  of  the  thumb,  and  on  the  right  hand  an  extra  joint  in  the  thumb. 
—  After  Bateson 

A  fifth  real  finger,  making  six  digits  in  all,  is  not  uncom- 
mon. Its  true  position,  however,  is  by  no  means  always  easy 
to  determine. 

Speaking  generally,  extra  digits  may  arise  in  three  ways,  — 
either  by  addition  to  the  series  of  an  outside  member  next  the 
thumb  or  the  little  finger,  by  the  insertion  of  a  member  at  some 
point  within  the  series,  or  by  the  doubling  of  a  member.  Just 
which  has  taken  place  in  any  given  case  is  not  always  easy  to 
determine. 

Reduction  in  the  number  of  digits  is  common  and  takes  place 
in  three  ways,  —  by  the  loss  of  an  outside  member  (generally 


MERISTIC  VARIATION 


55 


the  thumb,  when  the  radius  is  absent),  by  the  suppression  of 
a  member  within  the  series  (ectrodactylism),  or  by  the  union  of 
two  or  more  members  (syndactylism). 

Syndactylism  may  occur  in  all  degrees,  from  mere  webbing 
to  a  real  bony  union,  as  in  the  case  of  solid-hoofed  hogs.  Fig.  10 

A  T> 

/[  -O 


FIG.  10.    Degrees  of  syndactylism  in  digits:  the  general  shape  of  the  member  is 
preserved  even  when  one  digit  is  suppressed.  —  After  Bateson 

exhibits  a  case,  Z>,  in  which  the  normal  shape  is  preserved  in 
the  absence  of  a  member  (ectrodactylism),  with  nothing  to  sug- 
gest a  union ;  that  is  to  say,  digits  in  and  iv  seem  to  be  fully 
represented  by  a  single  digit,  normal  in  character  but  replacing 
two  members  of  the  usual  series. 


56  VARIATION 

To  fully  appreciate  the  significance  of  this  subject  we  need 
to  remind  ourselves  of  evolutionary  history  with  respect  to  digits. 

Man,  for  example,  has  normally  five  digits  in  all  extremities. 
The  same  is  true  of  the  bat.  The  ox  has  only  two  toes  and  the 
horse  but  one,  yet  there  are  rudiments  of  others  in  both  cases, 
strongly  suggesting  that  at  some  remote  period  the  number  might 
have  been  greater. 

All  things  considered,  it  looks  as  if,  for  some  unexplained  and 
at  present  unexplainable  reason,  animal  life  in  most  of  its  higher 
forms  had  been  originally  constructed  upon  a  plan  of  five  as 
regards  the  extremities.  True,  many,  if  not  most  species,  have 
long  since  departed  more  or  less  widely  from  the  original  plan, 
and  yet  the  numeral  five  is  as  distinctly  characteristic  of  the  digits 
in  animals  as  it  is  of  petals  in  the  rose  family  among  plants. 

How  this  number  has  been  gradually  reduced  to  a  final  form, 
sometimes  of  two,  as  in  cattle,  sometimes  of  one,  as  in  horses, 
is  a  chapter  in  development  that  belongs  to  the  ancient  history 
of  evolution.  Moreover  it  is  a  chapter  that,  for  obvious  reasons, 
must  be  read  backwards  and  reconstructed  from  its  fragments. 

It  will  assist  in  this  reconstruction,  and,  what  is  of  more 
consequence  to  the  breeder,  it  will  throw  much  light  upon  the 
manner  of  development  and  the  unit  of  variability,  if  the  stu- 
dent will  consider  the  present  condition  and  evident  ancestry  of 
a  few  characteristic  species  with  respect  to  digits. 

Bats  have  five  digits  in  both  wing  and  leg,  though  the  thumb 
is  modified  into  a  strong  claw. 

Birds  have  three  digits  in  the  wing,  namely,  i,  the  thumb, 
which  makes  the  so-called  bastard  wing;  n  and  in,  which  make 
the  true  wing ;  iv  and  v,  missing.  Radius  and  ulna  are  both 
present.  In  the  leg  the  fibula  is  a  mere  splint,  lying  by  the 
tibia. 

There  is  but  one  metatarsus,  but  it  is  large  and  heavy,  ending 
in  three  pulley-like  surfaces,  over  which  play  the  tendons  that  are 
attached  to  the  three  toes  directed  forward  (n,  in,  and  iv).  This 
plan  suggests  that  the  three  middle  metatarsals  of  the  normal 
foot  have  here  become  united  along  the  shank  into  one,  but 
with  three  surfaces  preserved  for  attachment  of  digits.  Most 
birds  have  also  a  toe  behind.  This  is  regarded  as  digit  i,  but 


MERISTIC   VARIATION  57 

no  bird  has  shown  a  trace  of  v.  Added  together,  this  all  means 
that  birds  have  lost  digit  v  from  the  leg,  if  they  ever  possessed  it, 
and  iv  and  v  from  the  wing,  with  i  in  a  fair  way  to  ultimately 
disappear  from  both  wing  and  leg,  except  when  functional  in  the 
latter. 

The  cat  has  normally  four  digits  (u  to  v)  on  each  foot,  all 
with  three  phalanges,  and  all  furnished  with  claws.  Besides  this, 
I  is  represented  on  the  fore  foot  by  a  pollex  (thumb)  of  two 
phalanges,  and  a  non-retractile  claw,  while  on  the  hind  foot  the 
hallux  (great  toe)  is  rudimentary,  consisting  of  a  small  bone 
articulating  with  the  cuneiform  but  bearing  no  claw.  Of  all 
animals,  aside  from  man,  the  cat  is  the  most  subject  to  supernu- 
merary digits,  especially  on  the  fore  foot.  In  the  great  majority  of 
cases  the  doubling  is  in  the  region  of  digit  I.  Often  the  extra  mem- 
ber is  shaped,  not  like  its  neighbors,  but  rather  as  if  belonging 
to  the  opposite  foot,  though  sometimes  it  is  indifferent.  For 
exhaustive  material  on  this  subject,  see  Bateson,  Materials  for  the 
Study  of  Variation,  pp.  313-324. 

Speaking  generally,  the  dog  tribe  has  five  toes  in  front 1  (digit 
i  not  touching  the  ground)  and  four  behind  (i  absent). 

The  seal  has  five  digits  on  all  extremities,  though  the  hand  is 
modified  into  the  flipper,  and  the  foot  is  but  slightly  functional 
and  evidently  well  on  the  road  to  extinction. 

The  whale  generally  has  five  digits  in  front  incased  in  skin 
to  form  a  flipper,  though  this  number  is  often  reduced  to  four, 
and  in  all  cases  n  and  in  have  more  than  the  usual  number  of 
joints.  The  only  traces  of  a  hind  limb  are  a  few  small  bones 
beneath  the  sacral  region  and  occasionally  a  part  of  a  limb.2 

In  the  manatee  and  the  dugong  the  process  has  gone  farther. 
Though  these  aquatic  mammals  have  exceedingly  serviceable 
flippers  with  five  digits,  yet  the  hind  leg  has  been  entirely  lost. 
The  vertebrae  in  the  sacral  region  are  not  united,  and  even  the 
pelvis  is  represented  only  by  a  pair  of  splint  bones,  though  some 
fossil  forms  show  a  rudimentary  femur  or  thigh  bone.3 

1  Excepting  the  African  hunting  dog,  which  has  four  (Lydekker,  Library  of 
Natural  History,  p.  496). 

2  This  is  similar  to  the  loss  of  wings  in  the  case  of  the  New  Zealand  apteryx. 

3  Lydekker,  Library  of  Natural  History,  p.  1156. 


58  VARIATION 

The  bear  has  five  toes,  all  round,  with  an  additional  claw  in 
digit  ii  behind,  which  he  uses  for  combing. 

In  mice  and  rats  digit  I  in  front  is  rudimentary.  This  case  is 
unique  because  in  most  instances,  where  a  difference  is  notice- 
able, the  reduction  in  digits  has  proceeded  farther  behind  than 
before. 

Snakes,  especially  the  large  ones,  occasionally  show  external 
vestiges  of  hind  legs,  and  internally  are  frequently  found  traces 
not  only  of  the  pelvis  but  likewise  of  the  thigh  bone  or  femur.1 
This  shows  clearly  that  the  snake  is  a  somewhat  recent  form 
developed  from  lizard-like  ancestors  with  limbs,  the  hind  pair  of 
which  must  have  been  placed  not  far  from  the  middle  point  of 
the  much-elongated  body.  This  view  is  strengthened  by  the  fact 
that  as  a  rule  but  one  lung  is  developed,  showing  that  the  body  is 
more  slender  than  formerly. 

Of  all  studies  in  digits  the  most  interesting  is  that  of  the 
ungulates  or  hoofed  animals. '  It  is  also  the  most  profitable, 
because  the  majority  of  our  valuable  domesticated  animals  are 
included  in  this  classification. 

The  interest  arises  from  the  fact  that  out  of  this  stock  have 
developed  two  very  different  forms  of  feet,  viz.  the  two-toed  (as 
cattle)  and  the  one-toed  (as  horses),  both  evidently  having 
descended  from  five-toed  ancestors,  each  by  a  process  of  its  own. 

For  example,  cattle,  sheep,  deer,  pigs,  etc.,  have  two  toes  (in 
and  iv)  well  developed  into  a  serviceable  foot,  with  two  others 
(n  and  v)  standing  behind,  not  touching  the  ground  (pigs),  often 
rudimentary  (deer),  and  frequently  represented  merely  by  splints 
(cattle).  Occasionally  all  trace  of  these  digits  is  lost  (giraffe). 

On  the  other  hand,  the  horse  and  his  kind  have  but  a  single 
toe  (in) ;  but  on  either  side  is  a  well-developed  splint,  the  re- 
mains of  the  second  and  fourth  metacarpals  in  front  and  of  the 
corresponding  metatarsals  behind.  They  are,  however,  without 
functional  significance,  being  attached  only  above  and  extend- 
ing downward  with  slender  shafts  and  free  ends  not  supplied 
with  digits. 

In  this  connection  it  is  to  be  noted  that  the  extinct  protohippus 
of  the  United  States  and  the  hipparion  of  Europe,  both  decidedly 

1  Lydekker,  Library  of  Natural  History,  p.  2535. 


MERISTIC  VARIATION  59 

horselike  animals  and  regarded  as  ancestors  of  the  modern  horse, 
had  each  three  toes  that  probably  reached  very  near  the  ground. 

Passing  still  further  back  (clown)  in  geologic  time  and  looking 
for  a  still  more  remote  ancestor,  we  get  beyond  what  can  be 
called  a  true  horse,  as  can  the  protohippus  and  the  hipparion. 
But  yet  there  is  among  these  long-extinct  forms  sufficient  horse- 
like  character  to  suggest  ancestry,  as  with  the  forest  horse  and 
desert  horse  of  the  Whitney  find  in  Wyoming,  forty  inches  high 
and  three  toes  down.1  As  we  progress  in  this  direction,  however, 
the  toes  increase  in  number  to  four  and  even  five,  clearly  indi- 
cating that  the  modern  horse  has  developed  from  a  five-toed  ances- 
tor like  the  Eohippus,  twelve  to  sixteen  inches  high  and  all  toes 
down,  also  discovered  in  Wyoming  where  it  flourished,  according 
to  Osborn,  some  three  million  years  ago  or  thereabouts.2 

If  we  begin  with  the  modern  two-toed  species  and  attempt  to 
read  their  story  backwards,  we  soon  land  among  the  same  four- 
or  five-toed  primitive  forms  just  mentioned,  forcing  the  conclu- 
sion that  the  one-toed  and  the  two-toed  species  of  recent  times 
have  each  descended  from  five-toed  progenitors,  —  indeed,  we  may 
even  believe  from  the  same  five-toed  progenitors. 

The  manner  of  this  descent  is  not  difficult  to  trace  by  the 
comparison  of  modern  species  with  similar  extinct  forms  in  suc- 
cessive downward  (backward)  geologic  times.  In  almost  the 
lowest  tertiary  rocks  of  both  North  America  and  Europe  occur 
fossil  remains  of  large  ungulates.  These  "  Coryphodons  "  were 
supplied  with  five-toed  feet  much  like  the  elephant  of  to-day, 
that  has  survived  by  virtue  of  his  teeth  and  in  spite  of  his  feet. 

Ascending  to  the  Miocene  Tertiary,  we  find  large  ungulates 
still  remaining,  but  digit  I  is  gone,  while  the  metacarpal  (or  meta- 
tarsal)  has  become  much  lengthened  and  the  third  and  fourth 
members  greatly  strengthened,  not  only  in  their  own  development 

1  Henry  F.  Osborn,  Origin  and  History  of  the  Horse. 

2  The  development  of  the  horse  from  an  ancestor  only  twelve  to  sixteen  inches 
high  and  with  five  toes,  all  down,  is  the  best  instance  of  progressive  evolution 
of  which  we  have  any  knowledge.    Doubtless  the  evolution  of  other  species  has 
been  no  less  extended  and  fascinating,  but  of  no  other  case  do  we  possess  so 
complete  a  history,  thanks  for  which  are  in  large  measure  due  to  the  generosity 
of  the  late  William  C.  Whitney  and  to  the  labors  of  Professor  Henry  F.  Osborn. 
See  also  chap,  x,  sect.  ii. 


60  VARIATION 

but  also  as  regards  their  articulation  with  the  small  bones  above. 
This  foot  is  now  on  the  road  to  becoming  indifferently  either  a 
two-toed  or  a  one-toed  form,  depending  upon  whether  n  and  v 
reduce  together  or  whether  in  takes  the  lead. 

In  this  connection  certain  intermediate  or  stranded  forms  are 
of  no  little  interest.  For  example,  the  elephant  has  five  toes  in 
front,  with  four  and  sometimes  three  behind.  The  rhinoceros  has 
three  both  before  and  behind,  but  the  extinct  form  often  had 
four.  The  tapir,  which  is  also  regarded  as  a  remnant  of  ancient 
life  preserved  until  the  present,  has  generally  three  toes,  though 
sometimes  four  and  occasionally  two.  In  any  case,  however,  digit 
in  is  largest  and  symmetrical  in  itself,  showing  affinity  with  the 
line  of  descent  that  has  developed  the  single-toed  forms. 

The  camel  has  two  toes,  while  the  nearly  related  chevrotain 
has  four,  two  being  reduced.  The  hippopotamus  has  four  short 
toes,  all  down,  all  hoofed  and  partly  webbed,  showing  affinity 
with  two-toed  forms  in  that  the  symmetry  is  about  a  line  drawn 
between  digits  in  and  iv.  This  is  the  same  plan  as  that  of  the 
pig,  except  that  in  the  latter  the  foot  is  more  contracted,  the 
toes  being  flattened  on  the  inside  and  the  second  pair  not  touch- 
ing the  ground. 

The  kangaroo  is  anomalous,  having  five  toes  in  front  and  in 
general  four  behind,  of  which  iv  is  much  the  largest ;  v  is  small, 
and  ii  and  in  are  much  reduced  and  incased  in  a  common 
integument. 

With  this  brief  survey  of  specific  differences  in  respect  to 
digits,  certain  individual  deviations  will  have  an  added  meaning. 
Bateson  gives  us  the  following  : 1 

1.  Horse  having  supernumerary  toe  on  inside  of  right  fore  foot,  presum- 
ably digit  ir.    It  articulated  with  an   extra  bone  in  the  lower  row  of  the 
carpus  and  was  provided  with  a  hoof,  "  convex  both  sides,  resembling  the 
hoof  of  an  ass"  (see  Fig.  1 1). 

2.  Foal  having  two  toes  on  each  fore  foot,  otherwise  normal.     The  car- 
pus was  in  this  case  normal,  but  the  extra  toes  were  again  borne  on  the 
inside  and  were  provided  with  a  small  hoof. 

3.  Horse  having  a  rudimentary  digit  on  inside  of  left  hind  foot.    This 
again  results  from  a  slight  development  of  digit  n,  which  is  the  most  com- 
mon cause  of  polydactylism  among  horses. 

1  For  variation  in  the  feet  of  the  horse,  see  Bateson,  Materials,  etc.,  pp.  360-372. 


MERISTIC  VARIATION 


6l 


More  rare  than  this  are  :  (i)  the  development  of  iv,  making  an  extra 
toe  on  the  outside  ;  (2)  development  of  n  and  iv,  with  in  normal,  making 
three  toes  in  all,  after  the  fashion  of  the  protohippus ;  and  (3)  development 
of  ii  and  iv  with  in  aborted,  resulting  in  an  abnormal  two-toed  foot.  All 
these  forms  are  well  known  among  horses. 

4.  Horse  with  supernumerary  on  outside  of  each  fore  foot,  illustrating 
condition  mentioned  above  (development  of  digit  iv)  (see  Fig.  12). 

5.  Horse   with   both   splint   bones 
bearing  digits  on  each  foot,  illustrat- 
ing condition  2  (n  and  iv  developed 
normal,  making  a  three-toed  horse). 


FIG.  ii.  Right  fore  foot  of  horse  (front 
view) :  as  the  hoof  of  the  horse  is  re- 
garded as  digit  in,  this  extra  member 
is  to  be  considered  as  digit  ii.  —  After 
Bateson 


FIG.  12.  Right  fore  foot  of  horse 
(rear  view)  :  this  extra  toe  is  to 
be  regarded  not  as  digit  ii  but 
as  digit  iv.  —  After  Bateson 


62 


VARIATION 


6.  Foal  with  right  fore  foot  bearing  two  complete  digits  symmetrically 
developed,  each  bearing  well-formed  hoofs  that  are  flattened  on  the  inner 
sides  and  curve  toward  each  other  like  those  of  the  artiodactyles  (cattle, 
etc.).  This  illustrates  condition  (3) 
just  mentioned  (see  Fig.  13). 

Cattle,  sheep,  and  pigs  af- 
ford deviations  no  less  inter- 
esting : 1 


FIG.  13.  Foot  of  horse :  digit  ill  sup- 
pressed, digits  ii  and  iv  developed.  — 
After  Bateson 


i.  Calf  having  three  digits    on 
right  fore  foot,  borne   on  a  single 

common  bone  after  the  fashion  of  the  birds  and  fully 
symmetrical  (see  Fig.  14). 

2.  Heifer  having  three  fully  developed  toes  on 
each  hind  limb.    In  this  case  the  supernumerary  was 
clearly  digit  n. 

3.  Calf  with  "supernumerary  toe  placed  between 
the  digits  of  the  right  manus  (fore  foot).    This  toe 

had  a  hoof  and  seemed  ex- 
ternally to  be  perfect,  but  on 
dissection  it  was  found  to 
contain  no  ossification,  but 
was  entirely  composed  of 
fibrous  tissue  and  fat."  2 

4.  Cow,  full-grown,  right 
fore    foot  with    four  digits 
arranged  in  two  groups  of 
two  each  (see  Fig.  15). 

This  is  clearly  a  case  in 
which  the  increase  is  due, 
not  to  the  reappearance  of 
an  ancient  lost  toe  like  n  or 
v,  but  rather  to  the  doubling 
of  the  normal  digits  ill  and 
iv  through  ordinary  meristic 
variation? 

5.  Calf,    left     hind    foot 
with    five    toes,    "an    inner 

three  digits  group  of  two  toes  curving 
toward  each  other,  and  an 
outer  group  of  three,  of 


FIG.  14.    Right   fore  foot  of  calf: 

present,  each   supplied  with  both  flexor  and 
extensor  tendons. —  After  Bateson 


p.  377. 


1  Bateson,  Materials,  etc.,  pp.  373-390.  2 

8  No  case  is  better  than  this  to  suggest  caution  to  the  student  of  evolution. 
When  an  extra  toe  appears  among  those  forms  whose  ancestors  were  known  to 


MERISTIC   VARIATION 


which  the  middle  one  was  almost  bilaterally  symmetrical,  while  the  hoofs 
of  the  other  two  turned  toward  it."  1 

Bateson  says  of  the  pig  that  he  knows  of  no  case  of  polydac- 
tylism  in  the  hind  feet.  All  cases  described  are  of  the  fore  feet, 
and  the  extra  toes  are  on  the  internal  side 
of  the  digital  series. 

Syndactylism  in  cattle,  sheep,  and  pigs. 
By  this  term  is  meant  a  real  union  of 
digits  ii  and  in  into  a  single  bone  incased 
in  a  single  hoof,  as  in  the  solid-hoofed  hogs. 

According  to  Rosenberg,  as  quoted  by 
Bateson,2  in  the  normal  sheep  "  the  meta- 
carpals  n  and  v  are  distinct  in  the 
embryonic  state,  afterwards  completely 
uniting  (fusing)  with  in  and  iv."  3  This 
throws  some  light  upon  the  whole  ques- 
tion, as  tending  to  explain  not  only  certain 
cases  of  polydactylism  but  all  cases  of 
syndactylism.4  Again  quoting  Bateson  : 

FIG.  1 5.  Said  to  be  the  right 

1.  A  young  ox  having  the  two  digits  of  the       forefoot  of  cow:  digits  in 
right  fore  foot  completely  united. 

2.  Calf:    each    foot  having  only  one  hoof, 
though  all  the  bones  were  normal. 

3.  Same  as  above,  except  that  in  the  fore  foot  the  normal  digits  (in  and 
iv)  were  completely  united,  bearing  a  single  hoof.    The  same  condition 
was  found  behind,  except  that  the  hoof  was  more  pointed. 

4.  A  fore  foot  and  a  hind  foot  of  the  same  individual  (pig),  in  which 
the  two  chief  digits  were  completely  united,  viz.  represented  by  a  single 
series  of  bones. 

possess  a  greater  number  of  digits,  it  is  habitual  with  many  to  regard  it  as  a  case 
of  atavism,  —  the  reappearance  of  a  long-lost  character.  But  how  is  it  in  the  case 
of  man  when  a  sixth  or  even  seventh  digit  appears  ?  This  must  be  meristic  varia- 
tion and  not  atavism,  because  no  six-toed  species  of  any  sort  has  ever  been 
described  or  its  existence  suspected.  Meristic  variation,  therefore,  is  not  limited 
to  lost  characters  or  to  numbers  once  normal,  but  may  go  far  in  excess  of  either. 
Here,  then,  is  need  for  discrimination,  for  even  the  appearance  of  a  character  that 
has  been  once  lost  is  not  absolute  evidence  of  atavism. 
1  Bateson,  Materials,  etc.  p.  381.  2  Ibid.  p.  383. 

3  The  former  from  failing  ever  to  unite,  the   latter  from  a  continuation  of  the 
fusing  process  to  include  in  and  iv. 

4  That  is,  ii  unites  with  in,  and  v  unites  with  iv  during  development. 


two  groups  of  two  each. 
—  After  Bateson  (from 
Delplanque) 


64 


VARIATION 


Other  and  similar  cases  are  given,  though  the  latter  is  the 
only  one  described  in  which  the  syndactylism  is  complete  in  all 
four  feet.  It  is,  however,  generally  simultaneous  in  fore  and 
hind  feet.1 

Absence  of  parts  in  a  linear  series.  Men  with  hands  but  no 
arms,  with  feet  but  no  legs,  are  not  unknown.  Whether  the 
missing  parts  are  really  dropped  out  of  the  series,  or  whether 

they  were  originally  present  but 
suffered  abortion  during  embry- 
onic development,  being  repre- 
sented at  maturity  by  rudimentary 
parts,  is  uncertain,  though  zoolo- 
gists would  incline  strongly  to  the 
latter  view.  The  exact  fact  would 
have  an  important  bearing  upon 
the  unit  of  variability,  the  nature 
of  heredity,  and  the  manner  of 
differentiation. 

Whatever  the  fact  in  this  re- 
gard, variations  of  this  order  are 
manifestly  rare  as  compared  with 
the  increase  or  decrease  in  strictly 
multiple  parts.  In  other  words, 
while  considerable  deviation  in  the 
number  of  similar  members  (as 

.    .  .  \' 

fingers)  is  common,  it  is  exceed- 
ingly uncommon  for  an  entire 

group  (as  the  hand)  to  be  omitted,  —  rarely  from  the  end  of 
the  series  (as  the  foot  or  hand)  and  still  more  rarely,  if  ever, 
from  the  middle  of  the  series,  as  would  be  the  case  in  a  truly 
missing  arm  (humerus,  radius,  and  ulna),  but  with  the  hand 
present,  coming  directly  from  the  body. 

Extra  legs.  The  repetition  of  a  member  as  complicated  as  a 
leg  is  extremely  unusual  but  by  no  means  unknown.  The  writer 

1  Bateson  gives  many  similar  cases,  each  with  some  peculiarity  of  its  own. 
Solid-hoofed  pigs  are  seen  so  frequently  and  at  points  so  widely  removed  both 
in  time  and  space  (mentioned  by  Aristotle  and  reported  from  many  regions  of  the 
earth)  (see  Bateson,  Materials,  etc.,  p.  387)  that  this  would  seem  to  be  a  variation 
that  has  often  arisen  afresh. 


FIG.  16.   Meristic  repetition  in  leg: 

.  right   leg   of    beetle    repeated   in 

triplicate.  -  After  Bateson 


MERISTIC   VARIATION  65 

saw  one  specimen  of  a  leglike  appendage  growing  from  the  left 
side  of  the  neck  of  a  calf  near  the  point  of  the  shoulder.  The 
leg  was  not  more  than  two  thirds  the  usual  length,  and  was 
twisted  and  functionless,  though  it  terminated  with  a  hooflike 
growth.1 

Extra  legs  are  common  in  insects,  sometimes  throughout  their 
entire  length,  sometimes  doubling  at  the  femur  (see  Fig.  16). 


SECTION  III  — MERISTIC   VARIATION   AND   BILATERAL 

SYMMETRY 

Meristic  variation  among  paired  organs  and  those  standing 
singly  on  the  median  line  throws  no  little  light  upon  the  nature 
of  bilateral  symmetry  and  also  incidentally  upon  the  manner  of 
variation. 

Speaking  generally,  paired  organs  may  double  on  either  side 
separately  or  on  both  sides  (digits,  legs,  wings,  etc.),  or  they  may 
unite  into  a  single  organ  with  its  axis  on  the  median  line  (horse- 
shoe kidney). 

Most  of  the  examples  of  meristic  variation  already  given  are 
of  repetition  in  paired  organs  in  bilateral  symmetry.  It  remains 
to  call  attention  to  the  opposite  condition,  —  the  fusion  of  a  pair 
into  a  single  organ  standing  on  the  median  line  : 

1.  A  good  example  of  this  is  that  of  a  roebuck  having  the  horns  com- 
pounded for  fully  half  their  length  into  a  single  "  beam  "  standing  on  the 
middle  line  2  (see  Fig.  17). 

2.  A  honeybee  3  having  the  two  compound  eyes  united  into  one  at  the  top 
of  the  head  with  no  groove  or  line  of  division  between  them.4 

3.  Posterior  ends  of  kidney  united  (in  man),  forming  a  horseshoe  kidney 
with  three  renal  arteries  on  each  side.    This  case  is  in  sharp  contrast  to 
Bateson's  No.  407,  with  a  single  large  kidney  on  the  left  and  two  smaller, 
one  below  the  other,  on  the  right. 

1  This  specimen  is  described  from  memory,  as  it  was  seen  before  these  phe- 
nomena were  matters  of  personal  interest. 

2  Bateson,  Materials,  etc.,  p.  460. 

3  Ibid.  p.  461. 

4  The  compounding  of  eyes  has  already  been  mentioned.    It  apparently  occurs 
only  in  insects,  but  is  a  good  example  of  the  development  of  highly  differentiated 
tissue  in  abnormal  situations,  illustrating  not  only  meristic  variation  but  functional 
variation  as  well. 


66 


VARIATION 


Conversely,  impaired  organs  standing  on  the  median  line  may 

be  divided  so  as  to  form  a  pair  of  organs  symmetrically  placed. 
It  should  be  noted  that  in  general  a  single  organ  standing  on 

the  median  line,  as  the  nose,  is  symmetrical  both  with  reference 

to  itself  and  to  the  median  line,  but 
that  for  the  most  part  paired  organs, 
though  symmetrical  with  reference  to 
the  median  line,  are  not  themselves 
necessarily  symmetrical  bodies  (ears, 
arms,  hands).  In  other  cases  of  paired 
organs,  however  (eyes,  kidneys),  the 
members  do  have  a  kind  of  symmetry 
of  their  own. 

Again,  nothing  is  more  common, 
especially  among  plants,  than  to  find 
a  single  organ  on  the  median  line 
appearing  as  a  paired  organ  in  cer- 
tain individuals  or  in  nearly  related 
species  or  varieties. 

Bateson  gives  as  examples  of  the 
last  the  posterior  petal  in  Veronica, 
which  in  most  related  species  appears 

FIG.  17.  Compounding  of  paired  as  a  pair  of  petals  lying  on  either  side 

organs:  the  two  horns  of  this       .    .  .  ,  ,,     ,. 

roebuck  are  united  into  a  single    of  the  middle  lme- 

beam  for  a  considerable  dis-       After  giving  numerous  instances  of 
tance,  but  afterwards  they  sep-  division  of    median  organs  in  fishes 

arate.  —  After  Bateson  .    .  .  .       .        r 

and  in  insects,  he  cites  authority  tor 

saying  that  "  The  organs  most  often  divided  in  man  are  the 
sternum,  neural  arches,  uterus,  penis,  etc.,  and  of  these,  speci- 
mens may  be  seen  in  any  pathological  museum.1  Organs  more 
rarely  divided  are  the  tongue,  epiglottis,  uvula,  and  central  neural 
canal."  2  These  latter  are  in  reality  cases  of  axial  duplicity.3 

1  Bateson,  Materials,  etc.,  pp.  450-458. 

2  Teratology  is  that  branch  of  biology  which  treats  of  abnormalities,  and  it 
affords  many  cases  of  extreme  variations.    This  study  has  been  considered  as 
curious  rather  than  profitable,  and  yet,  as  such  abnormalities  are  coming  to  be 
regarded  as  frequently  due  to  a  defective  germ,  it  may  yet  prove  that  attention  to 
cases  of  this  order  may  furnish  the  key  to  the  solution  of  questions  involving  the 
unit  of  variability.  3  Bateson,  Materials,  etc.,  pp.  559-566. 


FIG.  18.  Double-headed  turtle  compared  with  the  usual  specimens  two  to  three 
days  old.  Note  effect  on  shell  plates.  In  this  specimen  the  movements  of 
the  legs  on  opposite  sides  were  not  well  coordinated.  —  After  Bateson 


68  VARIATION 

Fig.  1 8  shows  a  case  of  double  head  in  the  turtle.  Many 
similar  instances  have  been  described,  but  this  is  especially  inter- 
esting because  "  the  two  heads  seemed  to  act  independently,  and 
it  is  said  there  was  no  concerted  action  between  the  feet  of  the 
two  sides."  The  same  phenomena  of  double  monsters  are  said 
to  be  frequently  noted  in  fish-hatching  establishments.  Among 
snakes  "  some  twenty  cases  are  recorded  of  complete  or  partial 
duplicity,  nearly  always  of  the  head.  Several  of  these  were  ani- 
mals of  good  size,  and  must  have  led  an  independent  existence 
for  some  considerable  time."  1 

Similar  cases  of  doubling  are  known  in  birds  and  even  in  mam- 
mals, but  among  these  higher  animals  the  practical  difficulties 
in  sustaining  existence  with  extreme  abnormality  are  very  great, 
and  they  commonly  do  not  long  survive. 

Between  this  division  of  a  single  organ  lying  on  the  median 
line  and  the  doubling  of  so  important  a  part  as  the  head,  there 
seems  to  be  no  clear  line  of  demarcation.  This  doubling  may 
even  go  further,  as  in  the  case  of  the  Siamese  twins,  until  the 
specimen  is  regarded  as  essentially  two  individuals  united  by 
some  sort  of  attachment. 

SECTION   IV —  SYMMETRY  IN  VARIABLE  PARTS 

Without  a  doubt  meristic  variation  in  one  organ  of  the  body 
is  likely,  but  not  certain,  to  be  accompanied  by  abnormality  in 
another.  For  example,  a  variation  among  the  digits  of  the  fore 
foot  is  likely  to  be  associated  with  a  similar  variation  behind,  still 
more  likely  on  the  opposite  side,  but  not  positively  with  either. 

Again,  there  is  some  suggestion  of  symmetry  within  the  part 
itself  in  which  the  variation  occurs.  A  good  example  of  this  is 
Bateson's  No.  495  (Fig.  19). 

This  is  a  left  hand,  and  the  four  extra  fingers  seem  to  repre- 
sent not  the  thumb  of  that  hand  but  the  fingers  of  the  opposite 
(right)  hand,  thus  seeming  to  aim  at  a  kind  of  secondary  sym- 
metry within  the  member.2 

In  the  description  of  this  case  we  are  told  that  this  double 
hand  and  arm  were  very  muscular,  so  that  it  was  not  possible 

1  Bateson,  Materials,  etc.,  p.  561.  2  Ibid.  p.  335. 


MERISTIC  VARIATION 


69 


to  decide  in  the  living  subject  whether  or  not  there  was  a 
doubling  of  the  bones  of  the  forearm.  The  eight  fingers  were  in 
two  groups  of  four  each,  with  a  wide  space  between.  The  two 
"  hands  "  were  thus  opposed  to  each  other  and  could  be  folded 
upon  each  other.  The  power  of  independent  action  of  these 
digits  was  limited,  showing  an  insufficient  supply  of  muscles.  If 
the  two  index  fingers,  iv  and  v  (really  n  and  n),  were  extended, 
the  other  six  could  be  flexed  ;  either  group  of  four  could  be 
flexed  independently  of  the  other,  or  the  three  fingers  of  either 


FIG.  19.  Symmetry  within  the  variable  part.  Here  it  would  seem  that  an  attempt 
has  been  made  to  repeat  the  hand,  or  rather  that  an  attempt  at  repetition  of 
the  thumb  has  resulted  in  a  doubling  of  the  hand. —  After  Bateson 

hand  could  be  flexed  alone.  The  index  fingers  alone  could  not 
be  flexed  while  the  other  six  were  extended. 

Bateson  gives  several  other  cases  of  "  double  hand"  (Nos. 
496-500),  all  giving  the  impression  that  the  doubling  is  not 
simply  of  digits  but  of  a  hand  as  a  whole.  His  No.  5  1 3  is  the 
case  of  a  double  thumb,  in  which  the  two  are  symmetrically 
opposed  to  each  other. 

It  is  unfortunate  for  our  purpose  that  so  large  a  proportion  of 
cases  cited  as  examples  of  meristic  variation  should  be  among 
human  subjects.  This  is  only  because  it  is  here  that  the  matter 
has  been  most  studied.  The  idea  has  been  advanced  that  domes- 
ticated species  are  more  variable  than  wild  ones,  and  man  more 
variable  than  his  simian  congeners.  The  point  is  not  well  taken, 
because  careful  study  shows  the  ape,  the  chimpanzee,  the  baboon, 
and  the  gorilla  to  present  the  same  meristic  deviations  in  respect 
to  digits  and  the  same  abnormalities  in  dentition  as  are  found 


;o 


VARIATION 


in  man.  Again,  while  digital  variation  is  exceedingly  common 
in  chickens,  it  is  rare  in  birds  generally,  and  is  almost  unknown 
in  ducks  and  geese  which  have  long  been  domesticated. 

The  fallacy  above  alluded  to  seems  to  have  arisen  from  the 
fact  that  domesticated  species  are  better  known  than  wild  ones, 
and  that  certain  variations  at  least  are  more  likely  to  be  preserved. 
In  any  event  they  are  more  strongly  impressed  upon  our  atten- 
tion. The  truth  seems  to  be  that  variability  depends  upon  the 
nature  of  the  part  and  the  relative  stability  of  the  species  in  ques- 
tion, not  upon  its  domestication  or  its  place  in  the  scale  of  life. 

We  can  therefore  avail  ourselves  of  any  material  bearing  upon 
the  general  question  wherever  it  may  be  found,  hoping,  however, 
for  the  early  coming  of  the  time  when  the  variations  within  the 
particular  field  of  thremmatology  shall  be  better  known  and  more 
accurately  described. 

Asymmetrical  development  in  symmetrical  parts.  The  case  of 
the  narwhal  illustrates  a  fact  in  variation  which,  though  seldom 
so  apparent,  is  doubtless  often  potentially  present,  and  if  so,  is 
certainly  to  be  reckoned  with  by  the  breeder. 

In  the  narwhal  the  canine  tooth  (in  the  male  only)  develops 
as  a  tusk,  often  attaining  a  length  of  seven  or  eight  feet,  or  half 
the  length  of  the  body.  The  peculiarity  is  that  normally  only 
the  left  tusk  develops,  and  in  the  few  cases  seen  in  which  both 
are  developed  the  right  tusk  is  spirally  twisted  from  left  to  right, 
exactly  like  the  left  tusk,  and  not  in  the  opposite  direction,  as 
we  should  expect.  What  is  still  more  astonishing  is  that  no  case 
has  ever  been  described  in  which  the  right  tusk  was  developed 
alone  instead  of  the  left.  Either  both  are  developed  or  the 
left  one  only,  and  in  the  former  case  they  are  essentially  both 
left  tusks. 

SECTION  V  — MERISTIC  VARIATION  IN  RADIAL  SERIES 

Except  in  the  lower  forms,  radial  series  are  characteristic  of 
plant  rather  than  of  animal  life.  In  the  branching  of  stems  and 
the  parts  of  flowers,  members  of  radial  series  are  everywhere 
about  us.  Their  variations  are  always  interesting  (doubling  of 
flowers)  and  often  exceedingly  valuable  (stooling  of  grain). 


MERISTIC   VARIATION  71 

Botanists  would  say  that  what  seem  to  us  as  radial  series, 
with  the  members  standing  on  the  same  horizontal  level,  are  in 
most  cases  really  shortened  stems,  bringing  these  parts  into  a 
relation  which  is  apparent  rather  than  actual,  as  would  happen  if 
we  could  telescope  any  long  stem  until  the  leaves,  regularly  dis- 
posed along  its  length,  should  come  to  occupy  the  same  plane.1 

In  this  view  of  the  case  the  petals  of  flowers  and  the  branch- 
ing of  stems,  as  in  the  stooling  of  grain,  would  be  examples  of 
linear  series  very  much  shortened  rather  than  of  radial  series, 
according  to  the  strictest  definition  of  the  term.  For  our  purposes, 
however,  this  structural  point  may  be  waived,  and  all  apparent 
cases  of  radial  symmetry  treated  as  actual. 

Observations  indicate  and  experiments  show  that  members  of 
such  series  may  be  increased  in  number  almost  indefinitely.  All 
the  members  may  be  doubled  simultaneously  (as  five  petals 
increased  to  ten),  or  any  one  member  (original  segment)  may 
double  or  even  triple,  or  it  may  be  entirely  suppressed  without 
reference  to  other  members  of  the  series. 

The  natural  method  of  doubling  seems  to  be  for  cell  division 
to  proceed  one  step  beyond  the  normal,  giving  rise  to  two  instead 
of  one.  If  this  occurs  in  all  the  members  (petals),  then  the 
members  will  all  be  doubled,  as  ten  instead  of  five ;  if  only  in 
part,  then  only  that  portion  will  be  affected,  making  six,  seven, 
or  even  eight  instead  of  five.  Thus  we  have  clover  running  all 
the  way  from  the  normal  three  up  to  as  high  as  seven  leaflets. 

Manifestly  if  cell  division  proceeds  two  stages  beyond  the 
normal,  each  of  the  twin  pair  again  dividing,  it  will  result  in 

1  Leaves  are  arranged  in  regular  order  upon  the  stems  of  plants  according  to 
a  system  constituting  the  mathematical  series,  |,  ^,  f,  f,  etc.,  in  which  the 
numerator  indicates  the  number  of  circuits  around  the  stem  to  reach  a  leaf 
directly  over  the  one  with  which  the  count  was  started,  and  the  denominator  the 
number  of  leaves  that  would  be  passed  in  such  a  circuit.  It  therefore  repre- 
sents the  number  of  members  in  a  whorl  of  a  shortened  stem  of  this  character. 

Corn,  for  example,  belongs,  with  all  other  members  of  the  grass  family,  to 
the  fraction  | ,  —  built  upon  the  plan  of  two.  This  number  runs  throughout  the 
plant,  and  while  the  number  of  rows  of  corn  on  the  cob  may  vary  freely  from 
eight  to  twenty-four,  no  case  of  an  odd  number  of  rows  has  ever  been  reported. 
This  fact  tends  to  set  some  limits  to  even  so  wayward  a  thing  as  meristic  varia- 
tion, which  seems  never  to  have  produced  an  ear  of  corn  with  an  odd  number  of 
rows.  This  seems  marvelous  when  we  consider  the  havoc  it  works  with  digits 
and  with  even  so  complicated  a  structure  as  a  head. 


72  VARIATION 

quadrupling  that  member  of  the  series.  If,  however,  only  one  of 
this  pair  should  divide  again,  we  should  then  have  one  plus  two, 
or  three,  new  parts  in  place  of  the  one  that  was  normal.  Again, 
if  all  four  should  start  and  one  abort,  it  would  likewise  result 
in  three  developed  members  instead  of  four  that  should  have 
appeared. 

All  these  various  processes  may  take  place,  but  whatever  the 
final  result,  and  whatever  number  ultimately  develops,  the  method 
is  that  of  doubling  through  cell  division,  giving  rise  naturally  to 
even  numbers.  Odd  numbers  are  explainable,  however,  by  sup- 
posing that  one  of  a  pair  continues  the  process  one  step  farther 
than  its  twin,  or  else  that  one  of  the  members  fails  to  develop. 
In  these  ways  an  original  member  of  a  radial  series  may  at  any 
time  develop  into  two,  three,  four,  or  more  ;  and  if  all  the  mem- 
bers take  part,  a  true  doubling  results. 

Meristic  variation  and  cell  division.  In  the  last  analysis,  there- 
fore, variation  in  the  number  of  members  in  a  radial  series  is 
reducible  to  questions  of  cell  division.  Indeed,  we  may  go  further 
and  note  that  all  cases  of  meristic  deviation  arise  in  this  manner  ; 
that  the  preservation  of  the  normal  number  of  multiple  parts 
depends  upon  successful  cell  division  up  to  a  certain  (normal) 
point  and  its  abrupt  cessation  at  that  point ;  and  that  all  sorts  of 
abnormalities  may  arise  through  excessive  multiplication,  through 
abortion,  or  through  some  other  disturbance  of  the  process  of 
cell  division. 

This  view  of  the  case  helps  to  explain  why  it  is  that  meristic 
variations  in  radial  series  are  among  the  easiest  to  explain  of  all 
variations  which  may  present  themselves  to  the  breeder. 

Considerations  of  this  character  make  clear  the  futility  and 
shortsightedness  of  appealing  to  reversion  or  atavism  to  explain 
what  may  be  a  mere  incident  in  cell  division,  —  an  incident,  more- 
over, .that  may  never  have  occurred  in  phylogeny,  may  not  be 
even  common  in  ontogeny,  and  is  therefore  not  to  unduly  im- 
press the  observer.1 

1  These  terms  will  be  frequently  used  in  the  text.  Phylogeny  refers  to  the 
development  of  the  species,  ontogeny  to  the  development  of  the  individual. 
The  latter  is  supposed  in  a  general  way  to  repeat  the  steps  of  the  former,  though 
with  this  view  of  the  matter  important  gaps  are  of  frequent  occurrence. 


MERISTIC   VARIATION  73 

SECTION  VI  —  IMPORTANCE  OF  MERISTIC  VARIATION 

Nothing  is  of  more  direct  benefit  to  man  than  the  stooling  of 
grain,  and  the  doubling  of  flowers  is  of  prime  importance  to 
students  of  the  beautiful.  Digital  variation,  and  indeed  most  of 
the  examples  among  animals,  are  not  only  of  no  practical  use  but 
they  constitute  deformities  that  would  at  once  be  eliminated  from 
the  fields  of  any  intelligent  stockman. 

Their  study  is,  however,  useful  to  the  student  in  two  ways : 
first,  as  showing  him  that  freaks  are  by  no  means  uncommon 
and  therefore  not  to  be  specially  prized  ;  and  second,  to  show 
the  manner  in  which  variation  operates  and  the  size  of  the  unit 
involved,  together  with  something  of  its  relations  to  other  and 
similar  units  in  the  same  body.  The  careful  student  will  not, 
therefore,  waste  his  time  in  trying  to  establish  a  race  of  solid- 
hoofed  hogs  the  first  time  a  specimen  of  the  kind  turns  up  in 
his  yard,  but  he  will  utilize  the  information  afforded  in  meristic 
variation  generally  to  advance  his  understanding  of  the  manner 
in  which  variation  behaves  and  of  the  relations  that  obtain  between 
the  several  parts  of  a  highly  differentiated  body. 

The  purpose  at  this  time  is  to  secure  a  mass  of  characteristic 
facts  on  which  future  studies  may  be  based.  Most  of  the  dangers 
of  erroneous  procedure  in  this  field  arise  from  a  paucity  of  well- 
authenticated  instances  and  from  restricted  views  of  their  real 
significance. 

Summary.  Meristic  variation  refers  to  deviations  in  the  plan 
or  pattern  on  which  the  organism  is  built.  Its  central  thought  is 
symmetry.  Symmetry  may  be  radial  with  the  members  identical, 
or  it  may  be  bilateral  with  opposite  members,  as  optical  images 
the  one  of  the  other.  Distinctions  of  right  and  left  arise  fr6m 
those  of  dorsal  and  ventral,  and  have  reference  to  the  relation  of 
the  individual  to  the  outside  world.  Organs  symmetrically  placed 
may  or  may  not  have  a  symmetry  of  their  own,  but  the  ten- 
dency is  for  a  part  to  establish  some  kind  of  symmetry  within 
its  own  members. 

When  parts  are  multiplied  they  may  be  like  the  other  mem- 
bers of  the  series  in  which  they  arise,  or  they  may  imitate  those 
of  neighboring  series  (homoeosis).  Repeated  parts  are  especially 


74 


VARIATION 


subject  to  meristic  variation.  The  general  plan  is  preserved,  but 
wide  variation  in  the  details  is  common,  as  in  the  nerve  branches 
from  the  spinal  column. 

The  part  repeated  may  be  simple,  like  a  digit ;  or  it  may  be 
an  entire  group,  as  a  whole  hand  or  an  entire  leg. 

Meristic  variation  has  its  seat  in  cell  division.  It  is  of  little 
utility  in  animals  though  highly  useful  in  plants,  but  its  phe- 
nomena are  valuable  for  the  insight  they  afford  into  the  man- 
ner of  variation,  the  general  persistence  of  plan,  and  the  unit  of 
variability. 

Exercises.  Let  the  student  give  ten  separate  examples  of 
meristic  variation  not  mentioned  in  the  text  and  describe  each 
fully,  stating  all  that  is  involved  of  symmetry,  homoeosis,  etc. 

ADDITIONAL   REFERENCES 

VARIATION.    A  cock  with  no  spurs  on  the  leg,  but  with  well-developed  ones 

on  either  side  of  the  comb.    By  E.  S.  Dexter.    Science,  VII,  136. 
VEGETABLE  TERATOLOGY.  By  Maxwell  T.  Masters. 


CHAPTER  V 

FUNCTIONAL  VARIATION 

By  functional  variation  is  meant  a  deviation,  not  in  form  or  in 
the  number  of  parts  but  in  the  functions  that  they  perform.  The 
living  animal  (or  plant)  not  only  is  something,  but  it  does  some- 
thing, and  plants  and  animals  differ  among  themselves  not  only 
in  what  they  are  but  in  what  they  do. 

Each  portion  of  a  highly  differentiated  organism  has  its  own 
peculiar  activity,  which  is  essentially  different  from  that  of  any 
other  part  of  the  same  organism.  These  activities  are  not  con- 
stant but  variable ;  and  inasmuch  as  many  animals  and  not  a 
few  plants  are  kept  not  for  their  appearance  but  for  what  they 
can  do,  any  deviations  in  their  performance  ability  are  of  prime 
importance  to  the  breeder,  who  is  bent  upon  their  increased 
efficiency  and  their  permanent  improvement  for  the  service 
of  man. 

Now  plants  and  animals  are  considered  as  high  or  low  in  their 
development  according  to  the  degree  of  differentiation  or  division 
of  labor  between  their  different  parts.  In  the  protozoon  the  func- 
tions of  life  are  few,  and  its  relations  to  the  environment  are 
simple.  Accordingly  its  activities  are  exerted  and  its  obligations 
to  life  discharged  by  the  common  mass  of  undifferentiated  pro- 
toplasm, perhaps  without  so  much  as  a  stomach,  reproduction 
being  effected  by  a  direct  division  of  the  whole  mass. 

In  higher  organisms  (metazoans),  however,  life  is  more  complex 
and  the  responsibilities  of  existence  are  heavier.  These  are  met 
by  specialized  structures,  such  as  the  mouth  to  take  food,  the 
stomach  and  intestines  to  dissolve  and  prepare  it  for  use,  the 
liver  to  convert  certain  portions  into  specially  usable  form, 
the  lungs  to  absorb  air,  the  blood  vessels  to  carry  it  and  the 
digested  food  to  all  parts  of  the  body,  where  each  extracts  what 
it  needs  and  can  use. 

75 


76 


VARIATION 


Then  there  are  organs,  as  the  kidneys,  whose  function  is  to 
remove  waste  products  that  would  otherwise  accumulate  and 
destroy  the  body.  There  are  others,  as  the  udder  and  various 
glands,  whose  function  is  to  manufacture  some  particular  product 
to  be  used  either  within  or  without  the  body.  There  is  a  system 
(the  muscular)  for  moving  the  body  as  a  whole  or  for  the  exercise 
of  any  of  its  parts,  and  a  network  of  nerves  forming  a  ready  and 
rapid. means  of  communication.  There  is  a  heart  to  drive  the 
blood,  and  perhaps  a  bony  skeleton  to  hold  the  complicated  mass 
together. 

Now  the  activities  or  functions  of  these  various  parts  are  by 
no  means  constant  and  invariable  from  day  to  day.  In  other 
words,  there  is  probably  as  much  deviation  in  function  as  in 
form,  and  for  the  purpose  of  the  farmer  it  is  even  more 
important. 

Evolution  not  a  study  in  morphology  only.  The  mistake  is 
often  made  of  defining  evolution  as  exclusively  a  study  in  mor- 
phology.1 It  means  more  than  that.  Living  beings  are  some- 
thing besides  form,  and  their  evolution  something  more  than  the 
development  of  their  form  ;  indeed,  in  their  service  to  man  both 
animals  and  plants  are  valued  less  for  their  structure  than  for 
their  function,  which  is  what  they  can  do.  And  so  it  is  that 

1  "  The  problem  of  development  is  an  acknowledged  morphological  problem." 
—  C.  B.  Davenport,  Experimental  Morphology,  Part  I,  Preface. 

The  conception  here  alluded  to  is  not  difficult  to  account  for.  The  idea  of 
evolution  or  development  as  opposed  to  the  older  assumption  of  special  crea- 
tion was  first  announced  at  the  very  close  of  the  eighteenth  century,  but  was  not 
generally  before  the  public  until  the  appearance  of  the  Origin  of  Species,  after  the 
middle  of  the  nineteenth  century  (1859).  At  that  time  biologists  were  chiefly  con- 
cerned in  classification  as  based  upon  external  structure  or  form.  It  is  not  strange, 
therefore,  that  the  discussion  should  have  first  arisen,  and  the  battles  incident  to  a 
new,  startling,  and,  in  the  popular  mind,  sacrilegious  theory  have  been  first  fought 
out,  in  the  field  of  morphology. 

Gradually,  however,  biologists  began  to  concern  themselves  more  and  more 
with  internal  structure  (histology),  and,  quite  to  their  surprise,  they  found  them- 
selves still  within  the  field  of  evolution.  Then  came  studies  in  function  (physi- 
ology)' showing  conclusively  that  this,  too,  is  a  matter  of  development  and  subject 
to  variation  and  heredity.  It  is  therefore  not  only  erroneous  but  for  the  breeder 
dangerously  misleading  to  consider  the  study  of  evolution  as  confined  to  the  field 
of  morphology,  which  is  not  the  exclusive  nor  to  him  even  the  primary  manifesta- 
tion of  the  great  principle  of  evolution.  There  is  evoluion  of  function  as  well  as 
evolution  of  form. 


FUNCTIONAL  VARIATION  77 

the  breeder,  intent  upon  enhancing  their  service  to  man,  sees 
in  the  variation  of  the  functions  natural  to  domesticated  animals 
and  plants  the  greatest  opportunity  for  improvement. 

So  true  is  all  this  that  the  successful  breeder  may  be  distin- 
guished from  the  novice  at  this  point.  The  latter  is  likely  to  be 
attracted,  first  of  all,  by  form  or  color,  because  differences  of  this 
sort  are  striking  and  easily  noticed  ;  while  the  former  will  always 
keep  foremost  in  mind  the  question,  Why  is  this  animal  (or  plant) 
valuable  to  man,  and  what  is  it  to  do  ? 

The  student  cannot,  therefore,  know  too  much  about  the 
natural  functions  of  domesticated  animals  and  plants  and  the 
deviations  to  which  they  are  subject.  He  should  know  this,  not 
only  as  a  guide  to  his  selection  but  also  as  constituting  valuable 
information  upon  the  nature  of  evolution  and  the  possibility  of 
influencing  the  causes  that  control  the  development  of  living 
beings,  functionally  as  well  as  structurally. 

Instances  of  variation  in  functional  activity  are  easily  divisible 
into  four  classes. 

1.  Variation  in  the  degree  of  activity  of  normal  functions 
between  different  individuals  of  the  same  species. 

2.  Variations  in  the  degree  of  activity  of  normal  functions 
within  the  same  individual. 

3.  Modification   of    normal    functions  by  external    or   other 
influences. 

4.  Normal  functions  exercised  under  abnormal  conditions. 

SECTION   I— VARIATION    IN  THE   DEGREE  OF  ACTIVITY 

OF  NORMAL  FUNCTIONS  BETWEEN  DIFFERENT 

INDIVIDUALS  OF  THE  SAME  SPECIES 

Variation  in  milk  secretion.  This  is  a  function  peculiar  to  one 
class  of  animals  (mammals).  It  is  the  product  of  a  highly  spe- 
cialized structure  and  is  practically  confined  to  the  female  sex. 
Moreover,  it  is  of  peculiar  economic  as  well  as  physiological  im- 
portance, and  there  is  no  better  example  to  bring  out  much  that 
is  involved  in  functional  variation. 

The  structure  of  mammary-gland  tissue  is  characteristic 
wherever  found,  but  the  quality  and  flavor  of  its  product  (milk) 


78  VARIATION 

are  not  the  same  for  any  two  species  (functional  variation  between 
species). 

Again,  no  two  individuals  of  the  same  species  can  be  depended 
upon  to  give  exactly  the  same  quality  of  milk,  for  herd  records 
show  that  the  milk  of  different  cows  varies  naturally  from  less 
than  3  per  cent  to  more  than  6  per  cent  fat l  (functional  varia- 
tion between  individuals).  Nor  is  this  dependent  upon  the  food 
supply,  for  all  authorities  agree  that  the  proportion  of  fat  to 
other  solids  is  dependent  upon  the  individual  and  not  upon  her 
feed.  Moreover,  differences  nearly  as  wide  as  these  quoted  may 
be  found  within  the  limits  of  a  single  herd  and  therefore  under 
identical  conditions  as  to  feed. 

Still  again,  two  individuals  of  the  same  breed  will  produce 
radically  different  amounts  of  milk  or  fat,  whichever  is  measured, 
from  identical  amounts  of  the  same  kind  of  feed.  This  has  been 
repeatedly  and  conclusively  shown  by  Professor  Eraser  of  the 
University  of  Illinois.2  Probably  no  fact  in  animal  physiology  is 
of  more  far-reaching  importance  than  is  this  marked  instance  of 
functional  difference  between  individuals. 

Three  experiments  were  conducted  in  the  attempt  to  deter- 
mine the  limits  of  this  difference  between  cows  considered  good 
enough  for  a  place  in  a  commercial  herd.  In  the  first  3  Eva 
produced  48  per  cent  more  milk  and  1 1  per  cent  more  butter 
in  ninety-one  days  than  did  Janet,  and  in  doing  so  consumed  no 
more  grain  and  but  7.6  per  cent  more  roughness.  These  cows 
were  both  mature,  were  fresh  on  the  same  day,  and  neither  suf- 
fered accident  during  the  experiment,  yet  Eva  produced  1057 
pounds  of  milk  and  12  pounds  of  fat  out  of  an  extra  feed  of 
112  pounds  of  hay  and  corn  stover,  —  a  difference  greater  than 
any  margin  of  profit  the  dairyman  may  hope  to  realize. 

The  second  experiment  was  a  comparison  between  Rose,  a 
native  cow  nine  years  old,  and  Nora,  a  native  cow  six  years  old.4 

1  The  actual  range  in  milk  is  far  greater  than  these  figures.    Single  milkings 
have  been  known  to  run  as  low  as  1.8  per  cent  fat,  and  Jersey  cows  near  the  close 
of  lactation  often  give  milk  with  9.0  per  cent  fat. 

2  See  Bulletin  No.  51  and  Bulletin  No.  66,  Agricultural  Experiment  Station, 
University  of  Illinois,  May,  1898. 

8  Ibid.  (51)  p.  103. 

*  Bulletin  No.  66,  University  of  Illinois,  November,  1901. 


FUNCTIONAL  VARIATION 


79 


Rose  commenced  April  13  and  Nora,  May  22,  1899,  and  both 
were  milked  for  a  full  twelve  months.  Both  were  in  good  health, 
and  both  continued  in  good  flow  until  the  last,  Rose  averaging 
over  1 8  pounds  of  milk  per  day  and  Nora  nearly  14  pounds  for 
the  last  seven  days  of  the  test.  Each  consumed  all  the  feed  she 
cared  to  take,  the  only  restriction  being  that  its  composition 
was  the  same  for  both.  Neither  was  in  any  sense  beefy,  but 
Rose  gained  181  pounds  and  Nora  165  pounds  from  August  I 
to  April  i ,  showing  that  they  were  evidently  working  at  or  near 
their  limit  of  milk  production.  The  grain  fed  was  corn  meal 
and  oil  meal,  and  the  roughage  consisted  of  clover-  hay,  rape, 
green  corn,  and  corn  silage,  always  in  combination  with  one  or 
more  of  the  following,  —  gluten  meal,  wheat  bran,  ajid  ground 
oats.  They  were  never  on  pasture  during  the  experiment,  and, 
as  has  been  stated,  the  feed  was  identical  in  quality  for  both. 

Rose  consumed  slightly  the  heavier  ration  and  yielded  decid- 
edly the  larger  product  both  in  milk  and  fat.  The  following 
table  exhibits  the  total  feed  consumed  and  the  product  yielded 
for  the  entire  period  of  twelve  months  : l 

COMPARATIVE  MILK  PRODUCTION  ON  BASIS  OF  FOOD  CONSUMED 


Cow 

FEED1 

MILK 

FAT 

BUTTER  l 

Rose       

64.77  Q2 

1  1,720  OO 

$6d  82 

6c8o<; 

Nora. 

618906 

7  7  CQ  QO 

29864 

"j"'Vj 
7J.8  ill 

Difference  .... 
Per  cent      .... 

288.86 
4.67 

3.570.00 
46.01 

266.18 
89.13 

3!0.54 
89.13 

Cast  in  verbal  form  this  means  that  Rose  was  able  to  produce 
47  per  cent  more  milk  and  89  per  cent  more  butter  than  Nora, 
with  the  consumption  of  but  4.67  per  cent  more  feed.  Reduc- 
ing both  to  the  same  basis  of  food  consumed,  it  appears  that 
with  a  given  amount  of  feed  for  every  IOO  pounds  of  milk  given 
by  Nora,  Rose  gave  139.5  pounds  ;  and  for  every  IOO  potmds  of 

1  Feed  in  pounds  of  digestible  nutrients.  Butter  reckoned  at  16.66  per  cent 
water,  adding  one  sixth  to  the  butter  fat.  Per  cent  of  difference  calculated  on 
Nora  as  a  base. 


8o  VARIATION 

butter  fat  (or  butter)  produced  by  Nora,  Rose  produced  180.7 
pounds.  For  purposes  of  milk  production,  therefore,  feed  was 
worth  39.5  per  cent  more  when  fed  to  Rose  than  when  fed  to 
Nora,  and  for  butter  production  it  was  worth  80  per  cent  more. 
This,  then,  is  the  true  measure  of  the  functional  difference 
between  these  two  cows,  and  it  is  good  and  sufficient  ground 
on  which  to  base  breeding  operations.  Further,  it  is  to  be  noted 
that  this  is  not  the  difference  between  a  good  cow  and  a  poor 
one  but  between  two  good  cows;  for  Nora  produced  348.4  pounds 
of  butter,  which,  as  Professor  Fraser  remarks,  is  nearly  three 
times  the  average  yield  (130  pounds)  of  cows  in  the  United 
States,  and  almost  one  half  more  than  the  average  yield  (250 
pounds)  of  what  are  considered  profitable  cows  in  Illinois. 

It  may  be  added  at  this  writing  (1906)  that  Rose,  though  used 
in  many  experiments  and  exhibited  at  various  state  fairs  and 
at  the  St.  Louis  Exposition,  is  still  living,  hale  and  hearty  at 
sixteen  years  of  age,  and  is  still  an  economical  producer  of  milk. 
She  has  an  average  yearly  record  of  384  pounds  of  butter  fat 
for  ten  years,1  and  though  she  has  been  in  many  tests  since  the 
one  just  reported  she  has  never  been  beaten  but  once.  That 
was  in  the  following  case,  which  bears  further  on  the  present 
point.  Three  cows  were  in  this  test  with  Rose,  —  Tina  Clay's 
Queen,  known  to  be  a  poor  cow,  and  two  natives,  known  as 
No.  i  and  No.  3,  supposed  to  be  two  of  the  four  best  cows  bought 
for  experimental  purposes  out  of  a  herd  of  one  hundred.  Reduced 
to  the  same  feed  basis,  and  taking  the  yield  of  Queen  as  100, 
that  of  No.  3  would  be  represented  by  121,  of  Rose  by  304,  and 
of  No.  i  by  3 12.  This  is  a  rate  of  more  than  three  to  one  against 
the  poor  cow,  or  over  two  and  one-half  to  one  between  good  cows 
on  the  same  feed  basis. 

This  difference  in  the  efficiency  of  individual  cows  is  depend- 
ent not  so  much  upon  daily  differences  as  upon  the  ability  for 
long-time  performance.  Some  cows  will  give  a  heavy  yield  for 
three  or  four  months,  and  go  dry  in  six  or  seven  months  ;  others 
will  give  a  profitable  yield  almost  continuously.  Both  extremes 
are  deceptive.  The  herdsman  will  almost  certainly  overrate  the 

1  Since  the  above  was  written  Rose  has  completed  a  twelve-year  record  of  7258 
pounds  of  milk  and  360  pounds  of  butter  fat  as  an  average. 


FUNCTIONAL  VARIATION  8 1 

former  and  underrate  the  latter,  so  prone  are  we  to  remember 
striking  and  maximum  data. 

These  are  not  isolated  and  peculiar  cases.  Professor  Eraser 
of  the  University  of  Illinois  tested  554  cows  in  36  commercial 
dairy  herds  of  the  state  for  a  full  period  of  twelve  months  each. 
He  found  that  the  best  25  per  cent  of  the  whole  number  tested 
were  able  to  produce  an  average  of  30 1  pounds  of  butter  fat  per 
year,  while  the  25  per  cent  of  lowest  efficiency  were  able  to  pro- 
duce an  average  of  but  133.5  pounds, — a  range  of  consid- 
erably more  than  two  to  one.  The  practical  significance  of  this 
difference  is  pointed  out  by  Professor  Eraser  as  follows  :  If  it 
costs  thirty  dollars  a  year  to  feed  the  poorer  cows  and  thirty- 
eight  dollars  a  year  to  feed  the  better  ones,  then  at  present  prices 
a  herd  of  twenty-five  of  the  latter  will  produce  as  much  net  pro  jit 
as  would  a  thousand  of  the  former.  A  little  calculation  will  show 
the  immense  saving  in  labor  in  keeping  the  smaller  herd,  and,  what 
is  equally  significant,  the  relatively  smaller  investment  in  animals, 
feed,  and  barns,  and  the  smaller  volume  of  business  generally. 

The  faculty  of  producing  a  high  yield  of  milk  manifestly 
depends  not  only  upon  the  activity  of  the  mammary  glands  but 
also  upon  the  capacity  of  the  stomach  to  handle  a  large  amount 
of  feed,  and  the  ability  of  every  organ  of  the  body  to  discharge 
its  normal  functions  regularly  and  to  endure  the  wear  and  tear 
of  sustained  exertion  under  heavy  pressure.  This  particular 
function  of  milk  production  is,  therefore,  a  kind  of  resultant  or 
algebraic  sum  of  many  body  functions,  and  we  should  not  expect 
to  find  its  maximum  except  rarely  and  in  few  individuals.  A 
simpler  function  practically  independent  of  others  would  there- 
fore be  unhampered  by  their  weaknesses,  and  it  would  reach  its 
maximum  in  a  higher  proportion  of  individuals. 

Variation  in  meat  production.  That  the  same  principle  is 
operative  in  meat  production  is  abundantly  shown  by  experi- 
ments. Steers  were  fed  separately  from  calfhood  to  full  maturity 
at  the  Michigan  Experiment  Station.1  The  experiment  was  com- 
menced as  a  breed  test  by  Professor  Samuel  Johnson,  and  com- 
pleted by  the  writer  as  a  test  of  individual  differences  in  ability 
to  put  on  gain  in  proportion  to  feed  consumed. 

1  Bulletin  Aro.  69,  Agricultural  Experiment  Station,  Michigan. 


82 


VARIATION 
GAIN  IN  PROPORTION  TO  FEED  CONSUMED 


STEER 

WEIGHT  AT  BEGINNING 

POUNDS  OF  GRAIN  TO 
ONE  OF  GAIN 

Jumbo 

6  Co 

616 

Colby     

840 

6.08 

Walton                 .... 

870 

7  OO 

Nick                    '    •    .     . 

74.O 

6  30 

Milton         

Q2O 

6.48 

Bov 

481; 

4  <;6 

•***/ 

Barrington  

Disco      

605 
440 

4-93 

4  78 

Differences  of  this  character  are  further  shown  by  Professor 
Mumford's  experiments  with  the  various  market  grades  of  steers.1 
Feeding  cattle  are  divided  in  the  markets  into  six  grades,  from 
fancy  selected  down  to  inferior.  A  car  load  (sixteen)  of  each  of 
these  six  grades  (ninety-six  animals  in  all)  were  fed  on  the  same 
ration  for  a  period  of  179  days.  The  animals  were  all  natives, 
though  the  better  grades  showed  a  much  higher  percentage  of 
good  blood  than  did  the  lower.  The  following  table  shows  the 
relative  ability  of  these  six  grades  of  steers  to  handle  feed  and 
convert  it  into  gain : 

RELATIVE  EFFICIENCY  OF  DIFFERENT  GRADES  OF  STEERS 


GRADES 

GAIN  PER 
STEER 

TOTAL  GAIN 
16  STEERS 

TOTAL  DRY  MAT- 
TER CONSUMED 

DRY  MATTER  rni< 
POUND  OF  GAIN 

Fancy 

460 

Choice  ..... 
Good    .     .     . 

455 

4IO 

/  JU^ 

7284 

88,093 

81  017 

V-V.) 
12.09 

I  -7    08 

Medium    .... 
Common  .... 
Inferior     .... 

381 

395 
35° 

wui 
6095 
6322 
5607 

79»535 
75^75 
72,494 

J3-°5 

12.00 
12.93 

Here  is  a  variation  of  over  31  per  cent  (460-350)  in  the  total 
gain  of  sixteen  steers  under  equal  opportunities,  and,  what  is 

1  Bulletin  No.  go,  Agricultural  Experiment  Station,  University  of  Illinois. 


FUNCTIONAL  VARIATION 


more  significant,  a  difference  of  over  30  per  cent  in  the  feed 
required  for  a  pound  of  gain.  This  shows  the  inferior  feeding 
quality  of  the  lower  grades,  due  partly  to  age  and  partly  to  lack 
of  breeding. 

Composition  of  corn  as  influenced  by  functional  deviation.  One 
hundred  and  sixty-three  good  seed  ears  were  selected  from  a 
strain  of  corn  known  as  Burr's  White.1  They  presented  to  the 
eye  no  more  differences  than  are  usual  with  seed  corn.  Three 
rows  of  kernels  from  each  were  analyzed  for  protein  and  also 
for  fat.  As  a  result  the  protein  in  the  various  ears  was  found 
to  range  from  8.25  per  cent  to  13.87  per  cent  and  the  fat  from 
3.84  per  cent  to  6.02  per  cent. 

-  COMPOSITION  OF  CORN  FROM  163  DIFFERENT  EARS 


CORN 
No. 

ASH 

PROTEIN 

FAT 

CARBO- 
HYDRATES 

CORN 
No. 

ASH 

PROTEIN 

FAT 

CARBO- 
HYDRATES 

76 

1.70 

10.05 

4-77 

83.48 

104 

i-54 

11.82 

4-43 

82.21 

77 

i-45 

10.42 

5.24 

82.89 

I05 

!-37 

12.36 

4.84 

81.43 

78 

'•55 

II.OO 

4.90 

82.55 

1  06 

L33 

11.15 

5.21 

82.3I 

79 

1.62 

10.89 

4.88 

82.61 

107 

9-47 

4.97 

84.23 

So 

1.63 

11.50 

4.58 

82.29 

1  08 

1.30 

11.04 

4.67 

82.99 

81 

1.47 

11.49 

4.26 

82.78 

109 

1-45 

10.82 

5.65 

82.08 

82 

11.78 

4-83 

82.00 

IIO 

i.  60 

12.81 

5.21 

80.38 

83 

1.17 

9.08 

4-05 

85.70 

in 

1.31 

10.76 

4-13 

83.80 

84 

1.51 

12.79 

4-25 

81.45 

112 

1.26 

10.48 

4-54 

83.72 

85 

1.46 

11.76 

4.94 

81.84 

"3 

I.IO 

9.30 

4-38 

85.22 

86 

1.50 

12.07 

4.61 

8l.82 

114 

1.33 

9.12 

4.10 

8545 

87 

J-59 

12.40 

4-74 

81.27 

"5 

1.29 

10.41 

4.17 

84.13 

88 

T-35 

9-34 

4-84 

8447 

116 

I.IO 

8.38 

4.88 

85.64 

89 

1.61 

10.71 

4.70 

82.98 

117 

1.42 

9-95 

4-23 

84.40 

90 

1.55 

9.90 

4-97 

83.58 

1x8 

1.44 

11.40 

5.02 

82.14 

91 

1.56 

10.68 

4.91 

82.85 

119 

J-55 

12.38 

4.62 

81.45 

92 

1.46 

12.96 

3-97 

8l.6l 

120 

r-39 

9-97 

4.42 

84.22 

93 

1.48 

11.80 

4.80 

81.92 

121 

1.36 

10.09 

4.82 

83.73 

94 

1.74 

11.89 

4-55 

81.82 

122 

1.36 

10.31 

5-25 

83.08 

95 

10.49 

82.45 

I23 

i-34 

9.68 

4.01 

84.97 

96 

i.  60 

II.  IO 

4-38 

82.92 

124 

1.44 

11.87 

4.61 

82.08 

97 

!-59 

11.84 

4.96 

81.61 

I25 

10.73 

4-53 

83.40 

98 

10.23 

82.87 

126 

1.49 

13-87 

5.72 

78.92 

99 

1.42 

8.40 

4.91 

85-27 

127 

1-43 

"•53 

4.31 

82.73 

100 

1.65 

12.28 

4.76 

81.31 

128 

J-33 

11.64 

4-57 

82.46 

101 

1.30 

10.08 

4.86 

83.76 

I29 

1.36 

11.25 

4.16 

83-23 

102 

1.49 

11.83 

4-51 

82.17 

I30 

i-35 

11.86 

5.oi 

81.78 

I03 

1.44 

11.25 

4-78 

82.53 

1.47 

10.49 

4.86 

83.18 

1  This  was  the  foundation  of  Dr.  Hopkins'  work  in  corn  breeding  at  the  Uni- 
versity of  Illinois,  as  reported  in  Bulletin  A'o.  j-j-  and  Bulletin  Aro.  too.  It  will  be 
further  discussed  later  on. 


84 


VARIATION 


COMPOSITION  OF  CORN  FROM   163  DIFFERENT  EARS  —  Continued 


CORN 
No. 

ASH 

PROTEIN 

FAT 

CARBO- 
HYDRATES 

CORN 
No. 

ASH 

PROTEIN 

FAT 

CARBO- 
HYDRATES 

132 

J-55 

11.13 

4-55 

82.77 

1  86 

1.48 

10.78 

4-74 

83.00 

I33 

11.13 

4.10 

83.38 

187 

1.28 

10.49 

4.44 

8379 

J34 

1.30 

10.85 

445 

83.40 

188 

i-53 

13.10 

5.51 

79.86 

13S 

l-37 

11.29 

4-53 

82.81 

189 

1.32 

9.58 

5^3 

83-47 

136 

1.59 

11-43 

5.10 

81.88 

190 

1.25 

11.50 

4-95 

82.30 

137 

1.47 

11.61 

4.41 

82.51 

191 

1.29 

11.19 

4-31 

83.21 

138 

1.36 

11.36 

4-53 

82.75 

192 

J-51 

11.49 

4.07 

82.93 

139 

!-57 

9.81 

5-23 

83.39 

193 

1.36 

9-47 

4-51 

84.66 

140 

i-34 

10.53 

4.18 

83.95 

194 

1.50 

11.47 

4-65 

82.38 

141 

1.45 

12.42 

4-5i 

81.62 

195 

1-54 

11.09 

4-37 

83.00 

142 

i-37 

9-3  i 

4.82 

84.50 

196 

1.30 

9-44 

3-95 

85.3I 

1.29 

n-33 

4.49 

82.89 

197 

1.26 

n.  20 

4.46 

83.08 

144 

1.42 

n-39 

4-99 

82.20 

198 

1.44 

10.23 

4-53 

83.80 

M5 

MS 

8.25 

4.81 

8549 

199 

1.29 

10.64 

4.67 

83.40 

146 

1.47 

11.29 

4-83 

82.41 

200 

10.13 

4.84 

83.64 

147 

1.26 

12.21 

4-49 

82.04 

2OI 

t-fi 

9.64 

5.22 

83.76 

148 

1.54 

11-94 

4-74 

81.78 

2O2 

11.26 

4.96 

82.39 

149 

1.36 

11.29 

4.08 

83.27 

203 

[ii 

10.48 

4-59 

83.67 

'5° 

1.44 

11.71 

4-03 

82.82 

2O4 

1.66 

12-57 

4.82 

80.95 

'51 

1.40 

9-31 

4.96 

84.33 

205 

1.46 

10.71 

5-36 

82.47 

1.41 

11.90 

4.09 

82.60 

2O6 

i-34 

10.27 

4-65 

83-74 

1S3 

12.51 

5.19 

80.95 

207 

11.09 

4.27 

83-39  ' 

'54 

1.42 

11.13 

5-02 

82.43 

208 

1.48 

12.05 

478 

81.69 

I5I 
156 

1-44 

11.05 
11.74 

4-53 
4.14 

82.98 
82.73 

2O9 
210 

1.48 
i-45 

10.22 

ii.  16 

4-3° 
475 

84.00 
82.64 

1.46 

IO.O2 

4.88 

83.64 

211 

1.48 

10.44 

4.21 

83.87 

158 

1.45 

10.66 

4-51 

83.38 

212 

1.27 

9-75 

4.12. 

84.86 

'59 

I.4g 

"•53 

4  65 

82.34 

213 

T-53 

12.40 

4-75 

81.32 

160 

i-43 

11.50 

4-83 

82.24 

214 

1.58 

'  IO.22 

4-43 

83-77 

161 

1.47 

n.  ii 

4-93 

82.49 

215 

9.22 

4.60 

84-73 

162 

1.48 

12.09 

5.61 

80.82 

216 

1.42 

IO.27 

4-35 

83.96 

163 

1.29 

10.78 

5-09 

82.84 

217 

1.32 

9-39 

4-83 

84.46 

164 

1.30 

9'36 

4-34 

85.00 

218 

1.40 

9-74 

4.71 

84.15 

165 

1.47 

10.50 

4-75 

83.28 

219 

1.37 

9.92 

4-32 

84-39 

1  66 

1.65 

11.29 

83.22 

220 

1-43 

9-63 

5-23 

83-71 

167 

1.37 

9-58 

4-72 

84.33 

221 

1.32 

10.33 

5.01 

83.34 

1  68 

1.49 

10.94 

4-34 

222 

1.41 

12.34 

4-57 

81.68 

169 

1.60 

11.79 

4.22 

82!39 

223 

1.49 

10.58 

4.64 

83-29 

170 

1.36 

1  1.  06 

4-39 

83.19 

224 

T-52 

11.36 

4-63 

82.49 

171 
172 

1.44 
i-45 

ii.  18 
12.28 

5-75 
3-99 

81.63 
82.28 

225 
226 

'•33 
1.36 

9.15 
10.31 

4-55 
5.08 

84-97 

173 

10.14 

4-35 

84.12 

227 

1.46 

12.63 

80.76 

174 

1.30 

10.19 

5.22 

83.29 

228 

1.41 

12.  16 

4.12 

82.31 

175 

1.40 

12.68 

5-29 

80.63 

229 

1.36 

11.04 

83.08 

176 

'•37 

9.86 

4-73 

84.04 

230 

i-43 

12.  IO 

4.29 

82.18 

177 

1.48 

13.06 

4-93 

80.53 

231 

T-33 

10.95 

4.60 

83.12 

178 

1.37 

10.93 

4.76 

82.94 

232 

1.52 

12.76 

4,10 

81.62 

179 

1.32 

11.87 

5-03 

81.78 

233 

1.40 

9-75 

'4.14 

84.71 

1  80 

i-39 

11.27 

4-55 

82.79 

234 

r-39 

10.78 

4.76 

83.07 

181 

1.47 

9.66 

4.21 

84.66 

235 

1.58 

9-97 

5-27 

83.18 

182 

1.37 

10.97 

3-94 

83-72 

236 

1.40 

10.18 

6.O2 

82.40 

183 

1-54 

10.32 

82.68 

237 

1.47 

ii.  16 

5.13 

82.24 

184 

1.44 

10.68 

4-89 

82.99 

238 

i.  60 

11.42 

5.20 

81.78 

185 

1.42 

9-33 

4-49 

84.76 

FUNCTIONAL  VARIATION  85 

The  wide  variation  in  all  constituents,  particularly  in  protein 
and  fat,  indicates  that  profound  differences  existed  in  the  func- 
tional activities  of  the  plants  that  produced  these  ears.  In  order 
to  determine  whether  these  differences  are  constitutional  and 
therefore  hereditary,  the  twenty-four  ears  highest  in  protein 
were  planted  (separately)  for  the  "high  protein  plot"  and  the 
twelve  lowest  for  the  "  low  protein  plot."  In  the  same  way  the 
twenty-four  highest  and  the  twelve  lowest  in  fat  were  planted 
for  "  high  fat  "  and  "  low  fat,"  respectively.  This  has  been 
continued  from  its  beginning  in  1896-1897  until  the  present 
(1907),  and  is  still  in  progress,  the  practice  being  each  year  to 
plant  separately  the  ears  that  show  the  highest  and  the  lowest 
values  in  respect  to  these  particular  constituents.  The  follow- 
ing table  shows  the  average  composition  of  the  seed  corn  and 
the  crop  for  the  first  year  of  the  experiment : 

PROTEIN 

Highest  protein  ear  out  of  163  analyzed 13-87 

Lowest  protein  ear  out  of  163  analyzed 8.25 

Difference 5.62 

Average  of  24  high  protein  ears  planted I2-54 

Average  of  12  low  protein  ears  planted 9.03 

Difference 3.51 

Average  of  crop  from  high  protein  seed 1 1 .  i  o 

Average  of  crop  from  low  protein  seed IO-55 

Difference .55     . 


FAT 

Highest  fat  ear  out  of  163  analyzed  .     .  ......     6.02 

Lowest  fat  ear  out  of  163  analyzed 


Difference  ...............  2.18 

Average  of  24  high  fat  ears  planted      ........  5-33 

Average  of  12  low  fat  ears  planted  .........  4-°4 

Difference  .........     .     .....  1-29 

Average  of  crop  from  high  fat  seed       ........  4-73 

Average  of  crop  from  low  fat  seed   .........  4-°6 

Difference  .  .......  6? 


86  VARIATION 

It  is  sufficient  for  the  present  purpose  to  note  that  there  was 
a  difference  of  5.62  per  cent  (13.87-8.25)  in  the  protein  content 
of  the  highest  and  the  lowest  ears  of  the  163  analyzed  ;  of  3.51 
per  cent  (12.54-9.03)  in  the  seed  planted ;  and  of  0.55  per  cent 
(11.18-10.55)  in  the  crop  harvested  the  first  year. 

It  is  not  the  intent  to  pursue  this  subject  further  at  this 
point.  It  will  be  fully  discussed  under  heredity  and  under  plant 
breeding,  but  enough  has  been  quoted  to  show  that  these  func- 
tional differences  are  both  distinctive  and  hereditary,  and  that  in 
it  all  the  ear  is  the  unit  to  such  an  extent  that  it  is  entirely  prac- 
ticable to  permanently  influence  functional  differences  by  selec- 
tion. Indeed  this  has  been  done  already  to  such  an  extent  that 
corn  has  been  produced  with  a  higher  protein  content  than  wheat. 

Variation  in  sugar  production.  Sugars  of  various  kinds  are 
produced  by  many  plant  and  animal  activities.  Certain  plants 
excel  in  this  particular  function,  and  among  these  wide  differ- 
ences have  been  found,  leading  to  marked  and  permanent  in- 
crease in  the  amount  of  sugar  produced.  The  beet,  for  example, 
though  originally  producing  but  from  4  to  6  per  cent  of  sugar, 
has  been  so  improved  and  its  sugar-producing  activities  have 
been  so  increased  as  to  yield  specimens  containing  as  high  as 
25  per  cent  of  sugar  and  whole  crops  averaging  14  per  cent. 

Cane  is  also  variable,  and  every  one  familiar  with  the  maple 
knows  that  certain  trees  will  yield  a  large  amount  of  exceed- 
ingly sweet  sap,  while  others  yield  but  little,  which  little  may 
be  either  sweet  or  tasteless,  —  indeed,  even  bitter. 

Variation  in  speed,  scent,  and  organic  activities  generally. 
One  horse  is  faster  or  more  enduring  than  another,  not  so 
much  from  conformation  as  from  inherent  activity  and  power 
of  endurance.  Some  dogs  are  especially  keen  in  scent,  others 
are  defective,  and  the  hearing  instinct  is  much  better  developed 
in  some  individuals  (dogs,  cats,  horses,  cattle,  birds,  etc.)  than 
in  others.1 

Mental  qualities,  personal  tastes,  and  intellectual  ability  in 
general  are  conditioned  not  upon  conformation  but  upon  the 

1  It  is  more  than  likely  that  some  of  these  differences  are  connected  with  the 
degree  of  development  of  certain  portions  of  the  nervous  system.  They  are 
none  the  less  functional,  however. 


FUNCTIONAL  VARIATION  87 

peculiar  action  of  certain  parts  possessed  by  the  race  in  com- 
mon, but  whose  special  functioning  in  each  particular  case 
determines  the  place  of  the  individual  in  the  scale  of  life. 

Variation  in  vital  functions.  For  present  purposes  the  animal 
body  may  be  regarded  as  a  colony  of  organs,  each  endowed 
with  its  own  peculiar  function,  the  life  of  the  whole  and  of 
every  member  being  dependent  upon  the  degree  of  success 
with  which  each  portion  does  its  work.  The  whole  is,  therefore, 
as  strong  as  its  weakest  member,  and  when  the  whole  is  put  to 
work  in  service  for  man,  that  service  will  depend  not  only  upon 
the  functional  activity  of  the  special  organ  involved,  as  the 
udder  or  the  muscular  system,  but  also  upon  the  successful 
discharge  of  all  vital  functions  when  subjected  to  the  unnatural 
strain  involved  in  working  under  pressure.  The  point  at  which 
the  machine  will  break  down  or  fail  to  do  successful  work  is, 
therefore,  a  matter  of  relative  strength  of  parts,  and  in  the  last 
analysis  the  limiting  element  in  performance  is  not  infrequently 
one  or  more  vital  functions,  which  experience  shows  are  as 
variable  as  are  other  and,  from  the  biological  standpoint,  less 
important  characters. 

The  beat  of  the  heart,  in  man  for  example,  though  steadily 
decreasing  in  rapidity  from  infancy  to  old  age,  yet  varies  be- 
tween different  individuals  at  maturity  all  the  way  from  less 
than  fifty  to  more  than  eighty  beats  per  minute.  Athletes  tell 
us  that  the  slow  beat  is  characteristic  of  long-distance  running 
and  sustained  effort  generally,  but  that  individuals  of  this  order 
are  ill  adapted  to  short-distance  running  or  other  work  requiring 
quick  response  to  stimulus. 

There  is  a  marked  difference  in  the  digestive  powers  of 
different  animals,  and  some  individuals  starve  because  the 
stomach  and  intestines  are  unable  to  dissolve  sufficient  food  to 
meet  the  demands  of  the  body,  —  and  there  are  all  degrees  of 
starvation.1  Others  with  excellent  digestion  but  with  limited 
powers  of  assimilation  fail  to  make  use  of  the  full  supply  that 

1  Wide  study  of  men,  animals,  and  plants  will  reveal  many  cases  in  which  the 
individual  has  accustomed  itself  to  an  abnormally  small  food  supply.  The  effect 
is  not  necessarily  fatal,  but  it  is  shown  in  reduced  output  either  of  labor,  body 
product,  or  other  form  of  organic  activity. 


88  VARIATION 

is  put  into  the  circulation.  In  the  case  of  Rose  and  Nora,  pre- 
viously cited,  what  did  Nora  do  with  the  excess  of  food  con- 
sumed ?  Digestion  experiments  with  individuals  indicate  no  such 
differences  in  digestion  among  healthy  animals  as  the  differences 
in  milk  yield  that  are  known  to  exist  between  cows.  The  only 
conclusion  is  that  in  a  case  like  this  the  surplus  food  passed  on 
out  of  the  body,  laying  excessive  labor  upon  the  excreting  organs 
as  well  as  incurring  loss  upon  the  one  who  provided  the  feed.1 

From  this  it  will  be  seen  that  the  excreting  organs  them- 
selves act  as  a  kind  of  safety  valve,  and  that  much  depends 
upon  their  relative  ability  to  discharge  their  functions  well. 
This  they  are  better  adapted  to  do  in  some  individuals  than  in 
others,  but  that  every  effort  is  made  to  keep  up  with  demands 
is  evidenced  by  the  fact  that  if  one  kidney  is  lost  the  other 
acts  for  both,  usually  increasing  in  size.  Speaking  generally,  a 
cow  will  give  as  much  milk  from  three  teats  as  from  four. 
Whether  this  is  from  compensation,  as  with  the  lost  kidney,  or 
whether  it  is  true  only  because  cows  are  seldom  worked  up  to 
their  limits,  the  data  at  hand  do  not  determine. 

The  tremendous  increase  in  the  activity  of  the  salivary  glands 
on  the  part  of  tobacco  chewers,  the  increase  in  size  of  muscles 
through  use,  and  the  marvelous  development  of  skill  in  eye  and 
hand  by  long-continued  practice,  as  in  the  playing  of  musical 
instruments,  reading  on  the  part  of  the  blind,  etc.,  —  these  are 
all  familiar  examples  of  functional  development  through  prac- 
tice. That  this  development  is  or  may  be  greater  in  some  indi- 
viduals than  in  others  is  too  well  known  to  need  more  than 
passing  mention  in  this  connection. 

Resistance  to  disease  and  invasions  of  the  animal  economy 
generally  differ  greatly  in  different  individuals.  Some  are  abso- 
lutely immune  to  certain  diseases,  others  peculiarly  susceptible. 

It  is  a  matter  of  common  observation  that  in  fields  of  corn 
killed  by  frost  an  occasional  stalk  remains  green  and  unaffected, 
showing  unusual  powers  of  resistance,  due  to  some  constitu- 
tional difference.  Without  a  doubt  these  are  the  differences 

1  This  is  conclusive  proof  of  the  fact  that  appetite  is  not  a  safe  guide  to  the 
amount  of  food  that  can  be  profitably  consumed.  The  most  that  can  be  said  is 
that  it  is  a  good  indication  of  body  use  among  animals  whose  efficiency  is  known. 


FUNCTIONAL  VARIATION  89 

that  go  far  toward  constituting  the  essential  distinction  between 
annuals  and  biennials  in  temperate  regions.  .    . 

And  so  it  is  that  the  value  of  an  animal  or  a  plant  depends 
not  only  upon  what  it  can  do  but  also  upon  its  powers  to  endure 
sustained  exertion ;  and  this  is  indirectly  dependent  upon  the 
vital  functions,  which  are  therefore  of  prime  consequence  to  the 
farmer.  The  horse  that  died  in  a  Michigan  coal  mine  at  fifty- 
four  years  of  age  after  having  worn  out  more  than  five  genera- 
tions of  harness  mates ;  Old  Granny,  the  Galloway  cow  that 
died  at  nearly  thirty -six  years  of  age,  having  raised  no  fewer 
than  twenty-five  calves ;  men  who  live  to  be  a  hundred  or 
thereabouts,  —  these  are  examples  not  of  individuals  that  have 
been  shielded  from  hardships,  but  rather  of  those  splendid 
pieces  of  animal  machinery  whose  every  part  easily  performs  its 
proper  function  to  any  limit  laid  upon  it  by  the  exigencies  of 
life.1  That  these  functional  differences  exist  and  that  they  are 
in  a  measure  hereditary  are  facts  that  challenge  the  most  careful 
attention  of  the  thoughtful  breeder. 

1  Benjamin  Franklin  Harris  died  of  pneumonia  in  Champaign,  Illinois,  May  7, 
1905,  at  the  age  of  ninety-three  years,  four  months,  twenty-two  days.  He  was 
personally  known  to  the  writer  as  remarkable  not  so  much  for  his  advanced  age 
as  for  the  fact  that  he  was  in  full  possession  of  all  his  powers,  and  actively 
engaged  in  business  until  within  a  wreek  of  his  death.  He  organized  the  First 
National  Bank,  which  at  his  death  was  operated  by  three  generations  of  the 
Harris  family  ;  but  he  was  president  to  the  last  in  fact  as  well  as  in  name,  and 
the  management  deferred  to  his  judgment  even  in  matters  of  detail. 

He  was  the  owner  and  operator  of  over  five  hundred  acres  of  prairie  land,  and 
was  one  of  the  earliest  and  largest  cattle  men  in  the  Middle  West.  He  was  a 
noted  feeder  before  a  market  wras  established  in  Chicago,  and  was  both  a  buyer 
and  a  seller  on  that  market  every  year  of  his  life  afterward.  He  was  always  a 
believer  in  heavy  cattle,  and  he  finished  and  sold  the  one  hundred  heaviest  cattle 
ever  marketed  in  this  country  and,  so  far  as  is  known,  in  the  world,  —  an  achieve- 
ment of  which  he  was  always  especially  proud. 

This  instance  of  longevity  is  given  not  as  an  extreme  in  respect  to  years  but 
in  respect  to  retention  for  so  long  a  time  of  all  the  powers  of  body  and  mind. 
Mr.  Harris  never  had  a  second  childhood,  and  was  a  good  example  of  what 
a  splendid  machine  is  the  human  organism,  which  ordinarily  breaks  at  the 
weakest  point  but  does  not  wear  out.  How  full  of  weak  points  animal  organ- 
isms really  are  and  how  weak  these  points  must  be  are  considerations  forced  upon 
the  mind  by  the  fact  that  Mr.  Harris'  span  of  life  was  more  than  three  times  that 
of  the  average  man.  These  three  instances  of  extreme  longevity  in  animals  and 
man,  showing  what  is  possible  in  animal  life,  afford  to  the  breeder  ample  food  for 
reflection. 


90  VARIATION 

Variation  in  fertility.  Certain  birds  regularly  produce  two 
eggs,  others  three,  and  still  others  four,  before  incubation.  The 
average  hen,  following  her  natural  habit,  lays  a  "  setting " 
(ten  to  fourteen)  and  then  suspends  for  incubation.  The  "  crop  " 
of  ova  has  been  laid,  and  time  is  required  for  another  to  come 
forward.  The  Maine  station,  however,  has  succeeded  in  greatly 
increasing  the  production  of  eggs,  and  has  produced  one  hen  that 
has  laid  two  hundred  and  fifty-one  eggs  during  a  single  year. 

Most  cows  produce  only  five  or  six  calves,  many  only  one  or 
two,  and  some  not  any,  yet  Old  Granny  (No.  I  in  the  Galloway 
Herd  Book)  produced  twenty-five,  the  last  one  in  her  twenty- 
ninth  year.  The  difference  between  regular  and  shy  breeders 
is  the  difference  'in  the  functional  activity  of  the  reproductive 
organs,  and  next  to  performance  ability  it  is  the  most  impor- 
tant character  in  the  eyes  of  the  breeder.  Even  longevity  itself 
is  not  its  equal  from  the  standpoint  of  the  improver,  because 
quality  cannot  be  said  to  exist  in  the  race  unless  the  individuals 
that  possess  it  are  sufficiently  fertile  to  insure  its  easy  and 
certain  perpetuation. 

Accumulation  of  functional  variations.  Having  shown  the 
marvelous  differences  in  functional  activity  between  different  in- 
dividuals, and  having  shown  that  these  differences  are  hereditary, 
as  in  corn,  it  follows  necessarily  that  functional  variations  may  be 
accumulated  into  true  breed  distinctions,  and  that  strains  of 
animals  and  plants  may  be  permanently  established  with  exceed- 
ingly high  efficiency  in  desired  lines  ;  indeed,  this  has  been  already 
accomplished,  though  we  are  still  far  short  of  what  is  possible. 

For  example,  the  beef  breeds  are  more  economical  producers 
of  meat  than  are  the  dairy  breeds,  and  the  converse  is  true  as 
to  milk  production.  These  two  functions  have,  therefore,  been 
largely  separated  along  breed  lines.  But  it  cannot  be  said  that 
one  beef  breed  is  more  efficient  than  another  in  meat  produc- 
tion, or  that  any  one  dairy  breed  stands  out  preeminently  as 
the  most  economical  producer  of  milk.  This  is  partly  because 
breed  differences  have  been  largely  built  up  along  lines  other 
than  those  of  efficiency,  and  partly  because  all  breeds  contain 
many  individuals  of  low  efficiency  in  their  own  breed  characters 
and  high  efficiency  in  those  of  other  breeds.  Some  Jerseys, 


FUNCTIONAL  VARIATION  91 

therefore,  are  better  feeders  than  certain  shorthorns,  and  there 
are  to  be  found  among  the  latter  breed  individuals  that  are 
more  economical  producers  of  milk  than  are  many  of  the  Jer- 
sey breed. 

It  has  been  said  that  no  race  was  ever  taken  by  a  part-bred 
horse  over  one  that  was  racing  bred.  Whether  literally  true  or 
not,  it  is  substantially  correct,  so  intensely  have  the  racing 
ability  and  instinct  been  developed  in  certain  breeds. 

These  facts,  together  with  what  is  known  as  to  corn  and  beets, 
show  clearly  that  much  yet  remains  to  be  done  in  the  way  of 
developing  functional  activity,  thereby  increasing 


SECTION  II— VARIATION  IN  THE  DEGREE   OF  ACTIVITY 
OF  NORMAL  FUNCTIONS  WITHIN  THE  SAME  INDIVIDUAL 

Of  no  less  scientific  or  economic  interest  than  the  data  given 
in  the  last  section  is  the  fact  that  functional  variation  is  by  no 
means  confined  to  differences  between  individuals.  The  prin- 
ciple applies,  though  to  a  less  extent,  to  the  individual  itself, 
whose  activities  are  not  constant  but  variable  from  day  to  day 
and  throughout  its  life. 

Daily  fluctuation  in  normal  functions.  It  will  be  found  upon 
investigation  that  the  ordinary  functions  of  the  body  are  unex- 
pectedly irregular.  Even  the  heart  action  is  not  absolutely 
constant  ;  it  is  slower  when  the  body  is  at  rest  than  when  it  is 
in  action  and  is  subject  to  great  acceleration  in  certain  diseases. 

All  organs  of  the  body  work  better  some  days  than  others ; 
indeed,  there  is  a  distinct  periodicity  with  each,  —  a  period  of 
increase,  followed  by  one  of  maximum  activity,  and  that  again  by 
one  of  subsidence.  This  is  the  way  organs  rest.  These  periods 
are  evidently  of  different  lengths,  and  it  is  therefore  only  occa- 
sionally that  the  body  as  a  whole  is  at  its  maxitmim.  A  good 
example  of  this  periodicity  with  functional  deviation  from  day  to 
day  is,  again,  that  of  milk  secretion,  which,  as  has  been  remarked, 
is  a  kind  of  resultant  of  all  the  activities  of  the  body.  The  fol- 
lowing table  gives  the  variations  in  the  quantity  and  character 
of  milk  from  a  single  cow  for  a  period  of  one  month.1 

1  Biilletin  No.  j/,  Agricultural  Experiment  Station,  University  of  Illinois. 


92 


VARIATION 


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FUNCTIONAL  VARIATION 


93 


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94 


VARIATION 


Comment  is  hardly  necessary  to  show  the  irregular  working 
of  the  animal  machine,  which  in  this  case  was  a  mature,  strong, 
and  healthy  cow.  The  per  cent  of  fat  varied  all  the  way  from 
2.7  to  4.2  within  the  space  of  twenty-four  hours. 

Influence  of  age  upon  functional  activity.  At  birth  the 
vital  functions  and  those  of  growth  are  at  their  maximum.  At 
this  time  growth  seems  to  be  proceeding  with  the  "  energy 
of  embryonic  development."  It  continues  at  a  maximum  for  a 
time,1  gradually  declining  in  rate  until  maturity,  when  growth 
of  the  general  body  ceases,  although  for  certain  parts  (hair, 
teeth,  horn,  hoof,  reproductive  cells,  etc.)  it  continues  nearly  or 
quite  through  life.  In  case  of  accident  many  parts  not  com- 
monly indulging  in  growth  after  maturity  are  able  to  regenerate 
with  more  or  less  success  (bone,  skin,  blood  vessels,  nerves), 
but  among  the  higher  organisms  generally  growth  practically 
ceases  at  maturity.2  It  is  for  this  reason  that  feeding  enterprises 
are  most  profitable  with  young  animals  that  are  still  growing. 
At  this  age  functional  activity  is  greater  and  general  bodily 
efficiency  higher. 

One  reason  why  the  lower  grades  of  feeders  are  less  econom- 
ical producers  than  the  better  grades  is  that  the  animals  are 
older,  the  difference  in  age  between  fancy  selected  and  inferior 
steers  being  one  to  two  years. 

Strength  and  endurance  are  evidently  at  their  maximum 
somewhat  after  maturity,  although  with  the  passing  of  that 
age  is  also  lost  something  of  the  power  of  rapid  recuperation 
and  repair. 

The  reproductive  functions,  undeveloped  until  a  considerable 
period  after  birth,  attain  a  high  degree  of  energy,  if  not  their 
maximum,  somewhat  before  full  maturity  is  reached.  They  then 
decline,  and  fail  entirely  in  old  age.  Their  duration  is  therefore 
considerably  less  than  the  life  of  the  individual,  often  dropping 
below  50  per  cent  of  the  full  life  period. 

1  The  curve  showing  rate  of  growth  at  different  ages  has  not  been  sufficiently 
worked  out,  but  enough  has  been  done  to  indicate  that  the  maximum  rate  of 
growth  is  attained  a  few  days  after  birth  and  that  this   maximum  is  never  again 
reached. 

2  Trees  continue  to  increase  in  size,  to  some  extent  at  least,  during  life,  illustrat- 
ing a  marked  difference  between  the  higher  plants  and  animals. 


FUNCTIONAL  VARIATION  95 

At  what  period  the  reproductive  functions  are  most  success- 
ful in  producing  young  of  a  high  order  of  excellence,  whether  in 
youth,  middle  age,  or  old  age,  is  not  determined,  though  it  is  a 
point  on  which  light  is  badly  needed.  It  is  certain  that  the 
practice  of  using  young  and  immature  sires  is  almost  universal, 
especially  among  cattle.  That  there  is  danger  in  continued 
reproduction  from  immature  animals,  even  though  they  are  sex- 
ually vigorous,  there  is  grave  reason  to  fear,  and  yet,  in  general, 
reproduction  antedates  maturity. 

The  duration  of  profitable  service  depends,  of  course,  upon 
the  nature  of  the  function  involved.  The  life  service  of  a  racing 
horse  is  manifestly  less  than  that  of  a  work  horse,  and  the  life  of 
a  meat  animal  is  less  than  that  of  one  kept  for  milk. 

Influence  of  exercise :  use  and  disuse.  The  beneficial  effect  of 
use  in  developing  and  perfecting  the  functions  of  the  body  has 
been  recognized  from  the  most  ancient  times.  Athletes  train 
for  this  purpose.  Musicians  practice  for  many  hours  every  day ; 
indeed  their  chief  labors  arise  from  the  need  of  constant  and 
severe  exercise  of  the  musical  faculties  in  order  to  achieve  any 
considerable  degree  of  perfection  and  to  hold  it  after  it  has 
been  acquired. 

Horses  designed  for  racing  are  worked  almost  from  the  first 
in  order  to  make  the  most  of  any  natural  ability  to  trot  or  run. 
Cows  are  believed  to  be  more  efficient  producers  of  milk  if  they 
begin  at  two  years  of  age  and  are  kept,  so  to  speak,  in  constant 
practice,  and  barrenness  is  believed  to  be  less  likely  if  heifers 
are  bred  early  than  if  left  to  attain  maturity  without  produc- 
ing young. 

Darwin  discovered  that  the  wing  bones  of  wild  ducks  as  com- 
pared with  their  leg  bones  were  relatively  heavier  than  those  of 
tame  ducks,  corresponding  to  their  respective  habits  of  life. 
The  arm  of  the  blacksmith  and  the  wing  of  the  ostrich ;  the 
remarkable  leg  of  the  kangaroo  and  the  remains  of  that  of  the 
whale  ;  the  brain  power  of  the  busy  man  and  that  of  the  slug- 
gard, —  these  and  scores  of  examples  that  might  be  cited  show 
not  only  that  exercise  develops,  quickens,  and  perfects  the  body 
functions,  but  they  show,  too,  that  their  very  retention  or  loss 
depends  in  the  long  run  upon  their  constant  and  rational  use. 


96  VARIATION 

Blind  people  acquire  a  quickened  and  an  educated  sense  of 
hearing  and  a  touch  that  amounts  almost  to  a  separate  sense. 
In  the  same  way  the  developing  of  the  bodily  functions  and 
activities  generally  depends  upon  judicious  use  (exercise) ;  and 
the  skill  of  the  trainer  and  the  results  he  is  able  to  achieve 
depend  not  only  upon  his  knowledge  of  methods  that  will  most 
certainly  insure  the  exercise  of  the  desired  parts  but  also  upon 
his  judgment  as  to  how  severe  and  protracted  that  exercise 
should  be  in  order  to  secure  the  maximum  effects  of  use  and 
not  incur  the  destructive  consequences  of  overuse.  This  is  as 
true  in  the  feeding  yard  as  upon  the  race  track,  and  applies  as 
well  to  the  raising  of  good  and  profitable  feeders  as  to  the  devel- 
oping of  racing  horses,  the  education  of  drivers  and  saddlers,  the 
training  of  hunting  dogs,  the  "  trying  out  "  of  homing  pigeons, 
or  the  teaching  of  canaries  to  sing  by  never  allowing  the  young 
birds  to  hear  a  false  note. 

Influence  of  feed  upon  functional  activity.  The  relation  of 
the  amount  of  feed  to  its  economical  consumption  is  a  subject 
needing  careful  investigation.  Enough  is  known  to  warrant  the 
assertion  that  animals  can  and  do  learn  to  take  amounts  far 
larger  than  can  be  really  used.  When  a  steer  consumes  over 
a  bushel  of  corn  a  day  he  has  simply  formed  the  eating  habit 
as  the  result  of  a  morbid  appetite,  nor  is  this  appetite  an  indi- 
cation of  body  needs  or  a  guaranty  of  its  powers  to  economically 
convert  the  feed  into  meat,  milk,  or  labor. 

It  is  significant  that  steers  very  gradually  brought  into  full 
feed  will  never  take  these  enormous  amounts.  Professor  H.  W. 
Mumford  of  the  University  of  Illinois  finds  that  under  such  cir- 
cumstances twenty  pounds  of  grain  per  day  is  all  the  animal 
will  take. 

Consumption  of  extreme  amounts  is,  therefore,  evidence  only 
of  the  quantities  of  feed  the  digestive  tract  can  carry  and  dis- 
charge without  calamity,  of  its  power  to  secrete  gastric  and 
other  digestive  juices,  and  of  the  ability  of  the  excreting  organs 
to  eliminate  unused  and  unusable  surplus  from  the  body 

In  the  case  of  Rose  and  Nora  the  latter  consumed  the  same 
feed  as  the  former  but  returned  but  little  more  than  half  as 
much.  She  was  undoubtedly,  from  the  standpoint  of  economy, 


FUNCTIONAL  VARIATION  97 

overfed,  but  whether  the  same  individual  would  make  cheaper 
returns  on  less  feed  is  not  so  well  known  as  it  should  be.  In 
the  mechanical  world  the  highest  return  of  energy  per  unit  of 
consumption  is  realized  when  the  machine  is  working  full  but 
somewhat  below  its  maximum  capacity.  Doubtless  the  same 
principle  holds  with  living  machines,  but  on  this  point  we  are 
sadly  in  need  of  accurate  information. 

On  one  point  we  are  certain.  The  animal  (or  the  plant)  is  able 
to  adjust  itself  to  a  wide  range  of  food  supply,  providing  the 
change  be  gradually  made.  Not  only  individuals  but  whole  fam- 
ilies for  generations  live  in  a  condition  of  semi-starvation,  often 
quite  ignorant  of  their  real  condition,  if  indeed  they  are  not  so 
indifferent  as  to  prefer  to  continue  in  the  old  way  rather  than  to 
disturb  their  tranquillity  by  increased  exertion.  Such  a  state 
may  easily  become  chronic  in  man  or  animal,  but  it  is  unprofit- 
able because  all  other  functions  are  suspended  or  reduced  to  a 
minimum  in  order  that  the  vital  functions  may  be  discharged  at 
all  and  the  animal  not  die  outright.  There  is  no  nicer  problem 
for  the  stockman  and  the  feeder  than  this  :  How  much  shall  I 
put  into  this  animal  machine  in  order  to  realize  the  highest  net 
efficiency,  after  first  providing  for  those  activities  which  are 
necessary  to  the  life  of  the  machine,  —  the  vital  functions  ? 

Influence  of  hard  conditions.  Under  hard  conditions  the  func- 
tions of  life  may  be  disturbed  but  not  destroyed.  Under  these 
conditions  valuable  activities  are  carried  forward  upon  a  reduced 
scale,  and  they  often  give  rise  to  losses  that  are  no  less  serious 
because  invisible.  The  most  common  example  of  this  is  in  the 
case  of  ill-fed  or  much-abused  animals  and  of  badly  nourished 
crops  or  trees  :  some  milk  is  secreted,  but  it  is  insufficient  and 
its  quality  is  poor ;  the  plant  is  weak,  with  little  resisting  power 
against  insects  or  disease,  and  with  little  ability  to  mature  its 
crop  ;  the  apples  are  there,  but  they  suffer  for  the  means  of 
development. 

Every  one  who  has  had  experience  with  unthrifty  animals  or 
plants  knows  how  difficult  and  how  slow  is  the  process  of  resto- 
ration of  normal  activity  after  it  has  once  been  seriously  checked 
by  neglect  or  disease.  This  is  because  the  condition  readily 
becomes  constitutional,  tending  to  continue  through  life. 


98  VARIATION 

SECTION    III  — MODIFICATION    OF    NORMAL    FUNCTIONS 
BY  EXTERNAL  OR  OTHER   INFLUENCES 

To  what  extent  are  normal  functions  dependent  upon  favorable 
environment  and  how  do  they  respond  to  changed  conditions  ? 
A  few  notable  facts  will  throw  some  light  upon  this  all-important 
question. 

Galls.  An  insect  stings  a  plant.  Under  the  influence  of  the 
poison  a  gall  is  formed.  If  this  gall  be  shown  to  a  biologist  he 
will  at  once  state  with  certainty  the  plant  which  produced  the 
gall  and  the  insect  that  made  the  injury,  so  definite  in  form  and. 
appearance  is  the  resulting  growth  and  so  distinct  is  it  from 
any  normal  growth  of  the  uninjured  plant. 

In  other  words,  specialized  plant  tissues  subjected  to  a  certain 
injury  produce  a  new  kind  of  growth  almost  as  specific  as  when 
operating  under  the  laws  of  heredity.  Here  the  functional  activi- 
ties of  the  plant  at  the  affected  point 'have  been  not  destroyed  but 
permanently  altered  in  such  a  manner  as  to  give  rise  to  new  struc- 
tures of  definite  form  and  often  with  specific  chemical  properties, 
as  in  the  case  of  nutgalls  *  containing  30  to  80  per  cent  of  tannin. 
In  cases  of  this  kind  a  new  function  has  been  developed  suddenly 
out  of  old  materials,  and  it  at  once  gives  rise  to  new  and  distinct 
products,  both  substantive  and  morphological. 

Abnormal  overgrowth  of  disordered  animal  tissues.  We  have 
just  noted  that  vegetable  tissues  subjected  to  specific  injuries 
often  suffer  such  a  derangement  of  their  functions  as  to  cause 
the  production  of  an  abnormal  but  characteristic  overgrowth  of 
the  injured  part.  Quite  similar  is  the  result  of  the  invasion 
of  the  animal  economy  by  specific  germs  from  without,  as  in 
the  case  of  Bacillus  tuberculosis.  Here  the  growths  (tubercles) 
resulting  from  the  apparent  attempt  to  encyst  the  foreign  material 
are  sufficiently  characteristic  to  serve  as  a  name  for  the  disease 
(tuberculosis). 

Tumors  generally,  whether  malignant  or  benign,  are  perverse 
overgrowths  of  normal  tissues  of  the  body,  whose  ordinary 

1  All  formulas  for  good  black  writing  ink  include  gallnuts  (or  nutgalls)  as  the 
characteristic  ingredient.  Those  commonly  used  are  produced  on  the  oak  by  the 
sting  of  the  gallfly  (Cy nips  galhr-tinctor ice). 


FUNCTIONAL  VARIATION  99 

functions  have  been  deranged  by  some  cause,  external  or  inter- 
nal, and  whose  activities  have  been  diverted  to  the  production  of 
abnormal  but  characteristic  tissue  with  "  no  typical  termination 
to  its  growth." 

Nearly  all  tissues  of  the  body 1  are  subjected  to  this  derange- 
ment of  their  ordinary  functions,  resulting  in  the  suspension  of 
all  activities  except  that  of  growth,  which  proceeds  with  the 
"energy  of  embryonic  development"  and  continues  indefinitely. 

Though  often  supplied  with  special  blood  vessels  and  a  system 
of  nerves,  these  growths  are  entirely  functionless  and  therefore 
useless  to  the  body.  Being  parasitic  they  are  always  a  drain 
upon  its  resources,  and  often  from  their  nature  or  position  they 
constitute  a  real  menace  to  its  existence. 

A  tumor  represents  a  bit  of  differentiated  body  tissue  that 
for  some  reason  or  other  has  abandoned  its  characteristic  func- 
tions, cut  loose  from  all  restraints  of  heredity,  set  up  an  inde- 
pendent existence  of  its  own  at  the  expense  of  the  colony  of 
which  it  has  been  a  respectable  and  dependable  member,  and 
has  now  devoted  all  its  resources  to  growth,  which,  as  has  been 
said,  proceeds  with  the  energy  of  embryonic  development,  result- 
ing in  nothing  but  functionless  masses  of  living  matter,  strongly 
suggesting  a  reversion  to  primitive  undifferentiated  tissue. 

Under  conditions  not  well  understood  all  sorts  of  abnormal 
growths  may  appear.  In  this  way  an  antenna  may  appear  where 
an  eye  ought  to  be,2  or  it  may  end  in  a  foot  instead  of  a  feeler.3 
^The  writer  knew  a  young  lady  of  culture  and  of  no  little  natural 
beauty  except  for  the  fact  that,  growing  from  one  cheek,  was  a 
tuft  of  coarse  black  hair  three  or  four  inches  long.  Her  normal 
hair  was  brown  and  her  complexion  clear.  What  functional  dis- 
turbance could  have  given  rise  to  such  a  growth  is  as  mysterious 
s  it  was  unfortunate. 

Ossification  is  a  natural  process,  but  under  the  influence  of 
excessive  strain  it  may  proceed  to  an  abnormal  extent,  as  in 
spavin,  where  the  entire  hock  joint  becomes  solid  through  the 
ossification  of  the  fluid  thrown  out  as  the  result  of  injury. 

1  Muscles,  fatty  tissue,  connective  tissue,  bone,  cartilage,  nerves,  glands,  blood 
vessels,  the  covering  of  the  brain,  etc. 

2  Bateson,  Materials,  etc.,  p.  151.  3  Ibid.  pp.  146-147. 


I0o  VARIATION 

Derangements  of  a  more  fundamental  nature  often  arise  dur- 
ing embryonic  development,  resulting  in  monsters  of  all  degrees 
of  abnormality.  Teratology  has  little  interest  to  the  biologist 
generally,  because  these  abnormal  caricatures  of  life  constitute 
nothing  but  sporadic  offshoots  of  the  species.  Developing 
from  defective  germs  and  having  no  connection  with  the  line  of 
descent,  they  are  of  little  interest  to  the  evolutionist.  Their 
interest  to  the  thremmatologist  lies  in  their  bearing  upon  func- 
tional activity  and  the  degree  of  certainty  with  which  specialized 
tissues  may  be  depended  upon  to  discharge  their  hereditary  and 
proper  functions. 

Variation  due  to  the  suppression  or  failure  of  the  reproductive 
functions.  The  abdomen  of  the  crab  Carcinus  mcznas  normally 
has  seven  segments.  In  the  female  these  are  distinct.  In  the 
male  the  abdomen  is  much  narrower,  and  the  divisions  between 
the  third,  fourth,  and  fifth  segments  are  obliterated.  Males, 
however,  inhabited  by  the  parasite  Sacculina  do  not  develop 
sexual  characters,  and  in  them  the  segmentation  is  complete,  as 
in  the  female.? 

A  young  male  is  castrated.  The  parts  removed  are  in  no 
sense  vital,  and  they  seemingly  have  no  connection  with  other 
organs  of  the  body.  All  the  bodily  functions  except  those  of 
reproduction  proceed,  but  not  as  before.  In  general  the  develop- 
ment of  the  shoulders  and  neck  will  be  arrested,  and  they  will 
remain  lighter  and  finer.  The  voice,  the  nervous  temperament, 
the  disposition,  and  the  general  activity  of  the  body  are  all 
affected.  The  mane  of  horses  will  be  thinner,  finer,  and  shorter. 
The  hair  of  face  and  neck  in  cattle  will  be  finer  and  less  curly. 
In  hogs  the  tusks  and  shoulder  plates  do  not  develop.  The  growth 
of  the  horns  is  lessened  in  sheep,  but  in  cattle  the  only  effect  is 
to  make  them  slightly  longer  and  a  little  more  slender,  ap- 
proaching the  female  type.  The  hinder  parts  of  the  body  as  a 
whole  develop  rather  more  in  castrated  than  in  entire  animals, 
and  there  is  a  general  approach  to  the  form  of  the-  female.  It 
is  noteworthy  in  this  connection  that  the  same  general  effect 
follows  the  failure  of  the  sexual  powers  with  advancing  age, 
except  that  the  body  development  has  already  taken  place. 

1  Bateson,  Materials,  etc.,  p.  95. 


FUNCTIONAL  VARIATION  IOI 

Females  deprived  of  their  ovaries  develop  to  some  extent  the 
characters  of  the  male.  Spayed  heifers  are  not  at  all  like  bulls, 
but  they  do  resemble  steers.  Unsexing  animals  seems,  therefore, 
to  induce  a  kind  of  mediocre  development,  although  it  gives  rise 
to  four  distinct  types  instead  of  two  for  each  species. 

Many  females  in  later  life  assume  certain  characters  of  the 
male.  Cows  bellow  and  paw  dirt  like  bulls ;  hens  grow  spurs 
and  try  to  crow  ;  women  sometimes  grow  a  straggling  beard  and 
acquire  a  heavy  voice.  These  changes  do  not  by  any  means 
appear  in  all  cases,  but  when  they  do  appear  they  may  be  regarded 
as  symptoms  of  loss  of  the  sexual  function  and  of  cessation  of 
breeding  powers.1 

This  influence  over  the  functions  of  the  body  by  organs 
apparently  having  no  connection  with  the  parts  affected  is  akin 
only  to  that  of  certain  glands  like  the  thyroid,  whose  function  is 
entirely  unknown,  but  in  whose  absence  children  -grow  up  defect- 
ive both  physically  and  mentally.2  We  are  at  this  point  very 
near  to  the  forces  that  determine  the  activities  of  living  matter, 
but  the  mysteries  involved  are  in  no  sense  cleared  up ;  they 
rather  deepen  instead  as  they  are  studied.  It  is  as  if  our  vision 
were  obstructed,  not  by  a  curtain  that  can  be  drawn  aside  afford- 
ing a  view  beyond,  but  rather  by  a  solid  wall  fixing  the  limits  not 
only  of  vision  but  of  progress  as  well. 

Functional  variation  due  to  the  modifying  influence  of  the 
conditions  of  life.  The  conditions  of  life  are  most  active  in  stim- 
ulating or  depressing  normal  activities,  but  they  are  not  without 
effect  upon  their  character  as  well.  Plants  having  a  fixed  abode 
are  more  dependent  upon  their  environment  and  therefore  less 
resistant  than  animals,  though  species  living  in  confined  waters 
are  little  better  off  than  plants  in  this  regard. 

1  Though  bearing  but  indirectly  upon  the  present  question,  it  is  worthy  of 
remark  at  this  juncture  that  many  individuals  of  each  sex  seem  to  be  naturally 
endowed  with  more  than  the  usual  proportion  of  the  characters  of  the  opposite 
sex  and  to  be  correspondingly  short  in  those  of  their  own.    Thus  we  have  our 
"  mannish  "  women  and  our  "  effeminate  "  men,  distinguished  not  only  for  their 
tastes  and  their  mental  characteristics  generally  but  for  their  body  conformation  as 
well.  These  abnormal  unions  of  male  and  female  traits  are  often  strange  mixtures 
indeed,  and  may  well  be  avoided  in  the  breeding  yard. 

2  Loeb,  Physiology  of  the  Brain,  p.  207. 


Vo2  ^  VARIATION 

Plants,  and  animals  too  for  that  matter,  growing  in  cold 
climates  or  under  hard  conditions  suffer  profound  changes,  to 
which  they  become  accustomed  (acclimated)  and  which  are  ever 
afterward  constitutional.  We  become  accustomed  to  cold  or  to  heat 
and  are  thereafter  less  affected  by  extremes.  Recent  calorimeter 
tests  show  that  the  temperature  of  the  human  body  is  lowest  from 
three  to  five  o'clock  in  the  morning  and  highest  from  one  to  three 
in  the  afternoon,  thus  following  fairly  close  the  minimum  and 
maximum  of  outside  temperatures.  These  conditions  continue 
even  if  the  subject  works  at  night  and  sleeps  in  the  daytime. 

Two  conditions  tend  to  produce  hard  and  spiny  growth  in 
vegetation.  These  are  intense  light  and  extreme  dryness.  Both 
are  found  in  tropical  regions,  and  when  they  occur  together  their 
maximum  results  follow  as  to  harshness  and  spines.  These  condi- 
tions can  be  verified  in  the  laboratory,  showing  conclusively 
that  the  character  of  growth  is,  in  a  measure  at  least,  dependent 
upon  surroundings. 

Speaking  generally,  plant  lice  reproduce  parthenogenetically 
during  the  growing  season  of  the  summer,  and  during  this  time 
only  wingless  females  are  produced.  With  the  approach  of  cold 
weather,  however,  a  winged  bisexual  brood  is  produced  that  lives 
over  winter. 

These  conditions  can  be  produced  artificially  in  the  greenhouse 
at  any  time  by  lowering  the  temperature  and  allowing  the  plants 
on  which  the  lice  feed  to  dry  up.  Thus  we  may  say  that  wings 
and  sex  may  be  developed  at  will  by  the  manipulation  of  the  condi- 
tions of  life. 

The  so-called  conversion  of  one  species  into  another  by  influ- 
encing its  environment  has  been  largely  overstated,  and  yet  the 
facts  are  that  when  Schmankewitsch l  grew  Artemia  satina  in 
water  whose  saline  content  was  gradually  increased,  the  caudal 
fins  and  their  bristles  "  progressively  degenerated  "  until,  in  many 
cases,  these  appendages  had  disappeared,  the  animal  thus  assum- 
ing the  character  of  A.  milhausenii,  which  normally  lives  in  waters 
of  extreme  density.  These  experiments  were  undertaken  because 
he  seemed  to  have  observed  this  transformation  taking  place 
naturally  in  a  lake  crossed  by  a  dam,  and  which  was  inhabited 

1  Bateson,  Materials,  etc.,  p.  96. 


FUNCTIONAL  VARIATION  103 

by  both  species,  the  one  above  the  other.  This  dam  broke, 
mixing  the  two  species,  but  in  three  years  original  conditions 
were  practically  restored.  The  experiments  were  undertaken 
to  learn  whether  real  transformation  had  taken  place  or  whether 
the  result  had  been  brought  about  by  selection. 

The  experiment  seems  convincing,  and  the  point  is  further 
strengthened  by  the  facts  that  Schmankewitsch  restored  the 
caudal  fins  by  reducing  the  solution,  and  that  when  the  reduction 
was  carried  below  the  normal  of  A.  salina,  within  three  genera- 
tions the  last  segment  of  the  body  divided  after  the  fashion  of 
A.  bmnchipus,  another  related  species.  The  facts  are  the  more 
remarkable  as  A.  salina  reproduces  parthenogenetically,  while 
A.  branchipus  is  not  known  to  do  so. 

Biologists  are  extremely  careful  not  to  assume  the  absolute  con- 
version of  one  species  into  another  by  any  such  direct  methods 
as  have  here  been  noted,  the  question  being,  rather,  whether  they 
are  all  good  species ;  but  that  single  characters  are  profoundly 
influenced  by  changed  conditions,  and  come  to  resemble  the  same 
character  in  another  and  related  species,  is  too  well  established 
to  be  longer  questioned.  What  light  this  may  finally  throw  upon 
the  origin  of  species  is  problematical,  but  it  serves  the  present 
purpose  in  showing  the  power  of  environment  to  profoundly 
modify  the  functional  activities  of  living  beings. 

If  a  cutting  of  willow,  currant,  or  other  suitable  growth  be 
planted  in  the  earth,  roots  will  start  from  the  part  below  the 
ground,  and  leaves  and  branches  from  the  part  above.  If,  now, 
it  be  cut  off  at  the  surface  of  the  ground  and  the  top  portion  be 
planted  again,  it  will  again  take  root  at  the  new  point  of  sever- 
ance which  had  before  borne  leaves.  The  process  may  be  con- 
tinued indefinitely,  or  until  the  piece  is  used  up,  showing  that 
roots  or  leaves  may  be  developed  at  will  at  any  point  along  the 
cutting,  according  as  it  is  placed  below  or  above  ground. 

If  a  cutting  be  planted,  roots  will  develop  only  at  the  lower  end. 
If,  however,  before  planting  it  be  cut  into  two  pieces,  each  will 
develop  roots  on  the  part  below  ground,  and  in  many  species  this 
will  occur  even  if  the  pieces  be  inverted  and  planted  top  down.1 

1  This  is  most  likely  to  take  place  in  young  wood,  less  likely  in  old  wood.  See 
Morgan,  Regeneration,  pp.  71-91. 


I04  VARIATION 

A  maple  tree  growing  in  Urbana  had  forked  into  two  nearly 
equal  parts  about  six  feet  from  the  ground.  One  part  was  split 
down  and  torn  off  in  a  heavy  storm,  when  it  was  seen  that  roots 
had  developed  in  the  crotch  and  were  evidently  at  work  upon  the 
soil  that  had  blown  from  the  street  and  the  moisture  that  had 
accumulated  from  rains. 

The  writer  was  excavating  for  a  basement.  A  black  cherry 
tree  stood  some  ten  feet  from  the  line  of  the  wall.  In  taking 
this  out  many  of  the  roots  were  severed,  their  cut  ends  being  left 
in  the  bank  of  undisturbed  earth.  In  a  few  days  these  cut  ends 
were  clothed  with  a  growth  of  green  leaves.  Here  was  tissue 
that,  under  normal  conditions,  functions  only  as  roots,  yet  upon 
occasion  readily  gives  rise  to  both  leaf  and  stem. 

All  plants  and  most  animals  maintain  definite  relations  to  light, 
and  if  free  to  move,  orient 1  themselves  with  reference  to  the 
direction  of  the  light  rays  striking  the  surface  of  their  bodies. 
A  plant  bends  toward  the  window  because  of  the  contracting 
effect  of  the  light  upon  the  protoplasm  of  one  side  of  the  stem. 
Many  larvae  are  negatively  heliotropic  ;  that  is,  the  lighted  side 
of  the  body  is  more  irritable  and  they  move  away  from  the  light, 
coming  to  rest  only  in  dark  places,  where  they  feed  and  mature. 
Others  are  positively  heliotropic  when  hungry  and  negatively 
heliotropic  when  fed.  Such  larvae  will  climb  trees  and  feed  upon 
the  leaves  or  buds  until  filled,  when,  becoming  sensitive  to  light, 
they  descend  and  hide  in  the  ground,  under  rubbish,  or  in  any 
other  place  shielded  from  the  sun.  This  action  has  been  errone- 
ously attributed  to  a  semi-intelligent  instinct.  It  is  nothing  but 
functional  dependence  upon  external  stimuli.  This  is  not  the 
place  to  pursue  the  subject  in  detail,  —  which  will  be  done  when 
discussing  "Instinct  and  Reflex  Action,"  — but  it  is  the  place  to 
note  the  wonderful  dependence  of  certain  normal  functions  upon 
external  influences. 

An  animal  is  invaded  by  a  foreign  germ  and  suffers  from 
disease.  It  is  in  most  cases  ever  after  immune  to  that  disease. 
What  change  has  been  worked  in  the  animal  economy  ?  We 

1  By  orientation  is  meant  the  direction  in  which  the  long  axis  of  the  body  is 
brought  to  rest  with  reference  to  surrounding  bodies  or  influences,  such  as  grav- 
ity or  light. 


FUNCTIONAL  VARIATION  105 

know  that  as  long  as  the  white  corpuscles  are  able  to  discharge 
their  proper  function  the  resistance  is  complete.  Why  do  they 
weary  of  their  work,  and  what  condition  is  left  behind  which 
assures  absolute  resistance  to  future  invasions  ? 

The  phenomenon  of  acclimatization  in  general  represents  a 
condition  in  which  an  organism  has  undergone  a  permanent 
change  in  its  vital  functions,  forced  upon  it  by  the  exigencies 
of  life.  In  the  future  studies,  however,  it  will  be  seen  that  the 
disturbing  effect  of  adverse  conditions,  if  not  too  severe,  may  be 
gradually  overcome,  and  the  animal  or  plant  resume  its  functions, 
either  modified  or  unmodified  ;  and  it  will  be  seen  further  that  if 
the  changes  be  gradual,  the  immunization  will  extend  to  a  point 
that  would  have  been  fatal  at  the  outset.  Thus  organisms  may 
be  reared  in  a  gradually  intensified  poisonous  solution,  or  in  a 
liquid  whose  temperature  is  slowly  raised,  and  in  this  way  a  point 
may  be  reached  many  degrees  above  the  power  of  normal  organ- 
isms to  withstand.  The  subject  cannot  be  pursued  further  in 
this  connection,  for  it  is  a  large  one,  with  many  other  bearings  ; 
but  the  student  should  bear  it  in  mind  throughout  the  study. 

Irregular  functioning.  An  interesting  phase  of  irregular  func- 
tioning is  found  in  the  so-called  "instinctive  acts,"  more  properly 
reflex  actions,  which  by  popular  conception  are  supposed  to  pro- 
ceed with  unerring  accuracy.  This  assumption  is  natural  in  view 
of  the  complex  nature  of  many  of  these  acts,  all  of  which  have 
the  appearance  of  being  under  the  control  of  reason.  For  exam- 
ple, note  the  complicated  nature  of  the  process  necessary  to  the 
successful  deposition  of  the  egg  of  the  yucca  moth  (Pronuba  yuc- 
caselld).  We  are  told1  that  these  moths  emerge  simultaneously 
with  the  flowers  of  the  yucca,  which  open  but  for  a  single  night 
and  are  practically  dependent  upon  this  particular  moth  for  ferti- 
lization. When  ready  to  oviposit,  the  female  gathers  a  bundle  of 
pollen  from  one  flower,  flies  with  it  to  another,  pierces  the  tissues 
of  the  pistil  of  the  latter,  and  lays  her  egg ;  after  which  she 
ascends  to  the  stigma  of  the  same  pistil  and  "  stuffs  the  fertilizing 
pollen  pellet  into  its  funnel-shaped  opening." 

Now  this  process  is  necessary  not  only  to  the  fertilization  of 
the  yucca,  but  also  to  the  grub  that  hatches  from  the  egg,  which 

1  Morgan,  Habit  and  Instinct,  pp.  13-15. 


106  VARIATION 

otherwise  would  be  left  without  food.  There  is,  therefore,  a 
particular  sequence  in  this  complicated  performance  that  must 
be  observed  or  failure  results ;  and  failure  is  fatal  to  the  exist- 
ence of  both  species. 

Moreover,  this  act  is  performed  but  once  in  the  lifetime  of 
the  moth,  who  has  no  knowledge  of  the  acts  of  her  predecessors, 
and  is  therefore  not  proceeding  from  simulation ;  nor  has  she 
opportunity  to  learn  the  fate  of  her  offspring  and  profit  by 
the  experience. 

Now  the  truth  is  that,  unerring  as  is  this  performance,  a 
good  many  ovules  escape,  from  failure  of  the  egg  to  hatch  or 
from  other  causes,  and  thus  the  yucca  is  able  to  mature  some 
seed.  That  complicated  processes  of  this  kind  are  not  always 
carried  out  in  proper  sequence  and  full  detail  is  shown  by 
careful  study  of  different  individuals,  as  pointed  out  especially 
by  Professor  C.  S.  Crandall  in  his  studies  of  the  apple  and  plum 
curculio.1 

Careful  study  of  these  complicated  acts  and  of  the  body 
functions  in  general  must  convince  the  student  not  only  of  their 
nice  adjustment  but  (what  is  of  equal  consequence)  of  their 
exceeding  variability  and  irregularity  within  limits  that  certainly 
are  by  no  means  narrow. 

Cases  of  "double  personality,"  in  which  the  individual 
behaves  for  a  time  as  another  and  distinctly  different  person, 
are  too  well  known  to  require  more  than  a  passing  notice. 
These  are  instances  in  which  an  entirely  new  set  of  functions 
is  brought  into  play,  —  distinct  from  the  normal,  yet  working- 
together  to  the  accomplishment  of  definite  ends. 

But  a  few  of  the  many  modifications  of  normal  functions 
have  been  mentioned.  This  is  not  the  place  to  exhaust  the 
subject.  Only  enough  has  been  given  to  show  the  student  that 
even  the  highly  specialized  functions  are  subject  to  the  laws  of 
variation.  The  matter  will  be  more  completely  covered  under 
"  Causes  of  Variation." 

1  Bulletin  No.  98,  Agricultural  Experiment  Station,  University  of  Illinois, 
pp.  500-502.  The  account  of  the  different  ways  in  which  three  different  females 
performed  their  work  is  given  in  full  under  "Transmission  of  Modifications," 
section  on  "  Habit  and  Instinct." 


FUNCTIONAL  VARIATION  107 

SECTION    IV  — NORMAL    FUNCTIONS    EXERCISED 
UNDER   ABNORMAL   CONDITIONS 

The  mammary  gland,  normally  confined  to  females,  is  com- 
monly functionless  until  after  pregnancy ;  but  by  manipulation 
of  the  udder,  heifers  and  other  females  may  be  made  to  yield 
milk  without  bearing  young.  Again,  rudimentary  mammae, 
present  generally  in  males,  are  occasionally  accompanied  by 
considerable  development  of  mammary  tissue,  nearly  always 
but  not  necessarily  functionless.1 

Most  remarkable  of  all,  mammary-gland  tissue  has  been 
known  to  develop  in  extremely  unusual  places  upon  the  body. 
Mammary  tumors  in  the  axilla  (armpits)  are  described  as  of 
"  common  occurrence  in  lying-in  women."  2  These  tumors  have 
no  duct,  but  in  squeezing  they  yield  "  both  colostrum  and 
milk,"  following  in  the  same  order  as  from  normal  mammas, 
and  oozing  through  the  skin  "  at  the  situations  of  the  sebaceous 
follicles." 

Besides  these  there  is  "  indisputable  evidence  of  the  presence 
of  a  mammary  gland  on  the  thigh  .  .  .,  on  the  cheek  .  .  .,  on 
the  acromion  (shoulder  point)  .  .  .,  and  in  the  labium  majus. 
...  In  the  two  last  cases  the  mammary  nature  of  the  gland 
was  proved  by  microscopic  examination."  3 

Similar  conditions  may  be  produced  artificially  by  grafting, 
and  all  sorts  of  abnormalities  may  testify  to  the  persistence 
with  which  highly  specialized  tissue  continues  to  discharge  its 
functions,  often  under  the  most  discouraging  circumstances.4 

For  example,  Hunter  and  Duhamel  grafted  the  spur  of  a 
young  cock  into  his  comb,  "  where  it  continued  to  grow  to  its 
normal  size."  5  "  Bert  transplanted  the  tail  of  a  white  rat  to 
the  body  of  Mus  decumanus  (the  common  brown  rat),  where  it 
continued  alive."  5  The  same  experimenter  bent  over  the  tail 

1  Dr.  Hottes,  a  personal  friend  of  the  writer,  knew  a  young  man  in  Germany 
who  was  suckling  an  infant. 

2  Bateson,  Materials,  etc.,  p.  185. 

3  Ibid.  p.  187. 

4  As  when  a  piece  of  mammary  gland  was  grafted  into  the  ear  of  a  guinea  pig ; 
when  the  pig  became  pregnant  the  gland  commenced  to  secrete. 

5  Morgan,  Regeneration,  pp.  178-179. 


I08  VARIATION 

of  a  rat  and  grafted  it  back  into  its  own  body.  After  it  had 
united  he  severed  it  at  the  normal  base  and  thus  provided  the 
animal  with  a  "  reversed  tail."  He  found,  however,  that  the 
tail  of  the  mouse  did  not  grow  as  well  in  the  body  of  the  rat  and 
would  not  unite  at  all  with  the  body  of  either  the  dog  or  the  cat.1 

Born  succeeded  in  uniting  the  anterior  and  posterior  parts  of 
the  tadpoles  of  two  different  genera  of  frogs  (Rana  esculenta 
for  anterior  and  Bombinator  igneus  for  posterior).  The  combi- 
nation lived  for  ten  days,  when  it  was  killed  because  of  patho- 
logical changes.2 

In  the  same  way  Harrison  made  up  an  individual  of  two 
species  (Rana  virescens  and  Rana  palustris).  This  he  kept  alive 
until  after  its  transformation  into  a  frog,  "  each  half  retaining 
the  characteristic  features  of  the  species  to  which  it  belongs."  2 
This  being  true,  it  is  not  surprising  that  many  varieties  of 
apple  can  be  grafted  into  the  same  tree  top.  Examples  of  this 
sort  might  be  multiplied  indefinitely,  as  in  the  making  up  of 
worms  by  grafting  together  pieces  of  two  different  species,  in 
which  each  piece  preserves  its  specific  characters ;  but  enough 
has  been  given  to  show  the  persistence  with  which  specialized 
tissue  continues  to  discharge  its  natural  function  even  under  the 
hardest  of  conditions.3 

The  circumstances  under  which  living  matter  can  discharge 
its  normal  functions  unaltered,  either  in  character  or  in  degree, 
and  the  limits  beyond  which  these  functions  must  cease  or 
undergo  alteration,  —  all  this  is  not  only  a  question  of  deep 
biological  interest  but  it  is  one  of  special  significance  in  breed- 
ing, because  it  throws  no  little  light  upon  the  real  nature  and 
causes  of  variability,  a  subject  upon  which  we  sorely  need  in- 
formation if  variations  are  ever  to  be  controlled  either  in  their 
development  or  in  their  transmission. 

Summary.  We  are  to  regard  variations  in  function  as  well 
as  in  form,  of  activities  as  well  as  of  structure,  of  what  an 
animal  or  plant  does,  as  well  as  what  it  is. 

The  body  functions  are  not  constant,  but  variable.  They  are 
variable  as  between  different  individuals  and  also  with  the  same 

1  Morgan,  Regeneration,  pp.  178-179.  2  ibid.  pp.  183-185. 

8  Ibid.  chap,  ix,  pp.  159-189,  "  Grafting  and  Regeneration." 


FUNCTIONAL  VARIATION  109 

individuals  at  different  times.  They  are  variable  not  only  in 
degree  but  also  in  kind,  and  normal  functions  may  be  disturbed, 
even  altered,  by  external  influences.  Conversely,  usual  func- 
tions may  be  discharged  under  most  unusual  conditions. 

All  variation  is  either  continuous  or  discontinuous,  and  contin- 
uity must  not  be  assumed.  Many  of  the  fundamental  qualities 
of  living  matter,  such  as  definite  composition,  argue  for  discon- 
tinuity. 

ADDITIONAL  REFERENCES 

IMMUNITY  AND  ADAPTATION.  Biological  Bulletin,  IX,  141-151. 
GELDINGS  MORE  SUSCEPTIBLE  TO  DISEASE  THAN  MARES.    Experiment 

Station  Record,  XI,  896. 

VARIATION  IN  IMMUNITY  TO   ANTHRAX  (among  sheep).     By  Martinet. 
%        Experiment  Station  Record,  XIII,  186. 
INSECTIVOROUS  PLANTS.    By  Charles  Darwin. 

For  good  evidence  on  functional  variation  consult  the  speed  records 
of  trotting  and  running  horses  and  the  Advanced  Registry  of  Jersey  and 
Holstein-Friesian  Cattle. 


CHAPTER    VI 

MUTATIONS 

SECTION    I  — DISTINCTION    BETWEEN    MUTATION 
AND   ORDINARY    VARIATION 

The  deviations  from  type  heretofore  considered  are  those  of 
individuals  rather  than  of  groups.  Whether  quantitative,  sub- 
stantive, meristic,  or  functional,  they  represent  the  fluctuations 
of  individual  members  of  a  species  or  a  variety  about  the  nor- 
mal type  of  the  race,  not  necessarily  exhibiting  any  tendency 
to  depart  permanently  from  that  type. 

The  study  of  these  deviations  shows  that,  while  no  two 
individuals  are  alike,  yet  the  departures  of  certain  individuals 
in  one  direction  are  compensated  by  departures  of  other  indi- 
viduals in  the  opposite  direction.  In  other  words,  the  members 
of  a  race  cluster  closely  about  what  may  be  called  a  center  of 
fluctuation,  which  is,  in  most  cases,  comparatively  stationary. 
Because  of  this  fact  we  may  have  a  relatively  fixed  type, 
indicating  a  practically  stationary  race,  even  in  the  midst  of 
considerable  individual  deviation.1 

Mutations,  on  the  other  hand,  mark  sudden  and  distinct 
departures  from  type.  The  pendulum  swings,  but  does  not  re- 
turn. A  new  center  of  fluctuation  is  established,  from  which 
individuals  deviate  in  all  directions  as  before.  It  is  not  that 
the  old  center  is  abandoned, — for  the  mass  of  individuals  still 
cluster  about  it  as  before,  —  but  it  is  that  a  new  center  is  estab- 
lished, about  which  a  new  group  clusters,  and  all  close  observers 
recognize  at  once  that  a  new  type  has  been  born  into  the  world 

1  This  fact  is  extremely  confusing,  especially  to  animal  breeders.  In  the  midst 
of  wide  variations  and  with  but  few  individuals  living  at  any  one  time,  the  breeder 
is  often  unable  to  tell  whether  his  general  average  (or  type)  is  improving,  retro- 
grading, or  standing  still.  This  matter  will  be  alluded  to  again  under  "  Type  and 
Variability." 

no 


MUTATIONS  1 1 1 

and  a  new  race  is  established  on  the  earth.  This  new  group 
and  its  center  constitute  a  mutation,  and  the  individuals  are 
spoken  of  as  mutants.  Variation  has  become  discontinuous  as 
well  as  continuous. 

These  sudden  offshoots  from  established  species  were  noted 
by  Darwin,  who  called  them  sports.  He  considered,  however, 
that  new  species  are  formed  only  by  the  slow  but  continuous 
action  of  selection  working  with  ordinary  fluctuations  (continuous 
variations),  building  up  new  types  a  little  at  a  time  through  the 
gradual  accumulation  of  slight  but  favorable  deviations. 

His  so-called  "  sports  "  were  therefore  mysterious,  and  from 
the  fact  that  under  natural  conditions  they  generally  disappear 
rapidly  by  crossing,  he  was  led  to  attach  little  importance  to 
these  sudden  departures  from  the  established  type.1  Later 
researches,  however,  have  given  them  unexpected  significance. 

The  distinguishing  feature  of  a  mutation  is  that  there  are  no 
intermediates  between  the  old  type  and  the  new,  which  was 
therefore  attained  not  by  slow  degrees  but  by  a  sudden  leap ; 
that  there  is  but  a  slight  tendency  to  revert  to  the  old  form, 
but  that  if  reversion  takes  place  at  all  it  is  complete  at  once  and 
the  return  is  to  the  old  type  and  not  to  an  intermediate  form. 
The  mutant  is  distinctly  a  case  of  discontinuity. 

SECTION  II  — EXAMPLES  OF  MUTATION 

The  classic  examples  of  mutation  are  the  weeping  willow  and 
the  nectarine.  They  are  to  be  regarded,  however,  as  familiar 
illustrations  of  general  principles  widely  operative  and  giving 
rise  not  to  few  but  to  many  distinct  types. 

When  a  seed  germinates  it  puts  out  two  sprouts.  One  is 
positively  geotropic  ;  that  is,  it  responds  to  the  force  of  gravity 
and  grows  downward  into  the  soil,  developing  the  root  system. 
The  other  is  negatively  geotropic ;  that  is,  it  grows  upward 

1  The  student  of  evolution  should  gain  the  conception  that  the  type  of  a  race 
is  not  a  fixed  point  from  which  deviations  radiate  ;  it  is  rather  the  center  of 
gravity  of  all  the  individuals  of  the  race,  its  exact  location  depending  upon  the 
extent  and  direction  of  individual  deviations,  shifting  slightly  from  time  to  time 
with  the  causes  that  influence  variability. 


I  i  2  VARIATION 

against  gravity,  and  with  an  energy  sufficient  to  maintain  it  in 
a  fairly  upright  position,  developing  stems,  branches,  and  leaves. 

Occasionally  this  latter  geotropism  fails,  and  the  branches 
hang  downward,  forming  a  "weeping"  variety.  This  is  espe- 
cially common  in  the  willow  and  the  birch,  though  by  no  means 
unknown  in  other  trees,  notably  the  elm,  maple,  and  beech. 

"  Cut-leaved  "  varieties  and  "fan  tops"1  occasionally  arise 
suddenly,  all  of  which  may  be  preserved  by  grafting  or  by  bud- 
ding, so  that  with  proper  attention  we  may  have  weeping,  cut- 
leaved,  and  fan-top  varieties,  not  of  a  few  but  of  many  species 
of  trees  and  shrubs,  although  the  readiness  with  which  a  partic- 
ular mutation  may  appear  in  one  species  is  no  guaranty  of  its 
appearance  in  another. 

A  tree  which  has  always  before  borne  peaches  may  suddenly 
bear  nectarines,  or  more  likely  a  single  branch  may  make  the 
departure,  the  remainder  of  the  tree  continuing  to  bear  peaches 
as  before.  In  any  event  the  mutation  may  be  propagated  by  bud 
or  possibly  by  seed, — in  which  latter  case  a  nectarine-bearing 
tree  results.  This  tree  may  bear  nectarines  all  its  life,  or  it  may 
occasionally  bear  peaches  on  the  whole  or  a  portion  of  its  top. 
The  significant  fact  is  that  there  is  no  intermediate  between  the 
peach  and  the  nectarine,  and  yet  the  one  may  arise  at  any  time 
from  the  other.2  The  mutation  from  peach  to  nectarine  is  clear- 
cut  and  distinct,  and  the  reversion  from  nectarine  to  peach 
when  it  occurs  is  equally  complete. 

The  apricot  appears  to  be  related  to  the  plum  much  as 
the  nectarine  is  to  the  peach.  In  both  cases  the  main  stocks 
(peaches  and  plums)  exist  in  many  varieties,  and  the  mutations 
(nectarines  and  apricots)  in  but  few.  In  the  case  of  the  former 
(the  peach)  the  main  stock  is  downy,  while  the  mutant  is  gla- 
brous, or  destitute  of  downy  covering.  In  the  latter,  however, 
the  conditions  are  reversed,  for  the  main  stock  (the  plum)  is 
glabrous,  while  it  is  the  mutant  that  is  downy. 

1  A  fan-top  tree  is  one  in  which  the  branches  are  borne  on  opposite  sides,  after 
the  fashion  of  corn.    In  a  small  forest  plantation  belonging  to  the  writer  is  a  fan- 
top  linden,  now  grown  to  considerable  proportions. 

2  Inasmuch  as  the  peach  is  considered  as  the  main  race,  the  nectarine  is  said 
to  arise  from  the  peach  by  mutation.    Therefore  when  peaches  are  borne  upon 
nectarine  trees  the  case  is  considered  to  be  one  of  reversion. 


MUTATIONS  113 

Because  the  apricot  has  never  been  observed  to  arise  direct 
from  the  plum  as  the  nectarine  has  repeatedly  been  known  to  arise 
from  the  peach,  and  because  the  apricot  trees  have  never  been 
known  to  bear  plums  as  the  nectarine  trees  occasionally  bear 
peaches,  — because  of  these  facts  botanists  have  quite  generally 
ceased  to  regard  the  apricot  as  a  sport  from  the  plum,  and  are 
agreed,  I  believe,  in  considering  it  as  a  distinct  species. 

However,  it  behaves  precisely  like  a  mutant,  and  in  consider- 
ing the  means  by  which  new  types  originate  the  presumptive 
evidence  is  strong  that  the  apricot  originally  sprang  from  the 
plum  stock.  Though  it  is  true  that  some  mutations  are  fre- 
quently repeated,  it  is  also  true  that  others  arise  but  rarely. 
The  nectarine  is  unusual  in  the  frequency  with  which  it  reap- 
pears, and  the  readiness  with  which  the  peach  and  its  mutant 
exchange  places  has  perhaps  no  parallel. 

In  many  respects  the  apricot  appears  like  an  intermediate 
between  the  peach  and  the  plum.  The  external  appearance  of 
the  fruit  is  that  of  the  peach.  The  pit  is  smooth,  resembling 
that  of  the  plum.  The  bark  of  the  tree  is  like  that  of  the  peach, 
but  the  leaf  is  like  that  of  the  plum.  There  is  nothing  to  sug- 
gest a  hybrid  origin,  though  everything  to  suggest  that  this 
strange  plant  and  its  fruit  are  in  some  way  composed  of  the 
elements  of  both  the  peach  and  the  plum. 

Nor  would  a  hybrid  origin  be  at  all  necessary  to  this  fact. 
Certain  characters  are  general,  running  through  many  species 
quite  independent  of  consanguinity.  Thus  the  weeping  or  the 
cut-leaved  habit  is  common  to  a  great  variety  of  species  only 
remotely  related.  The  downy  character  is  common  with  both 
fruit  and  leaf,  and  almost  every  downy  or  pubescent  species  has 
its  glabrous  or  smooth  variety,  —  its  mutant  in  all  probability, 
and  one  that  easily  and  frequently  arises.  So  also,  without 
doubt,  the  reverse  is  true  by  which  smooth  species  occasionally 
throw  off  downy  or  pubescent  varieties.  Now  this  particular 
character  of  pubescence,  while  simple  enough  in  itself,  is  yet 
exceedingly  noticeable,  and  serves  to  insure  a  specific  name, 
unless  indeed  the  direct  origin  happens  to  be  extremely  well 
known,  in  which  case  the  mutant  is  likely  to  get  off  with  a 
varietal  distinction. 


114  VARIATION 

In  the  same  general  manner,  color  is  likely  to  fail,  and  nothing 
is  more  common  in  nature  than  albino  varieties.  Thus  we  have 
our  white  currant,  strawberry,  raspberry,  and  even  the  black- 
berry, —  almost  every  thicket  affording  its  examples  and  speak- 
ing eloquently  of  the  freedom  with  which  nature  creates  new 
forms,  and  if  we  will  only  open  our  eyes  to  see  what  is  going  on 
about  us,  we  shall  learn  much  of  how  it  is  done. 

Albinism  among  animals  is  even  more  common  than  among 
plants.  Men,  dogs,  cats,  horses,  cattle,  sheep,  bears,  rabbits, 
rats,  mice,  and  many  other  species  are  distinguished  by  albino 
varieties. 

These  distinctions,  marked  though  they  are,  arise  doubtless 
from  the  simplest  causes.  For  example,  if  an  animal  for  any 
reason  fails  to  secrete  pigment  in  the  normal  manner  it  is  from 
necessity  an  albino,  and  if  the  failure  is  hereditary  an  albino 
race  is  likely  to  be  established,  although  unrestricted  breeding 
greatly  reduces  its  probability  through  crossing  with  other  forms. 

SECTION   III  —  EXPERIMENTS  OF   DE  VRIES  1 

Hugo  De  Vries,  professor  of  botany  in  the  University  of 
Amsterdam,  long  ago  became  convinced  that  Darwin's  theory 
of  the  origin  of  species  through  the  gradual  accumulation  of 
fortuitous  variations  is  not  the  only  means  of  creating  new  types. 
Darwin  taught  not  only  that  existing  types  had  been  preserved 
by  selection  because  they  in  some  way  fitted  the  conditions  of 
life,  but  that  the  intervening  spaces  between  species  and  varieties 
represent  extinctions  through  the  agency  of  natural  selection. 

De  Vries  came  to  believe  that,  in  many  cases  at  least,  the  new 
type  springs  suddenly  from  the  old,  without  gradation  and  without 
intervening  forms,  and  that  while  selection  may  shape  up  the 
new  type  and  perhaps  the  better  fit  it  for  existence,  yet  the 
selective  process  is  in  no  way  responsible  for  its  origin.  Indeed, 
one  of  the  earliest  evidences,  to  his  mind,  that  new  types  often 
arise  without  the  agency  of  selection,  was  the  notable  fact  that 
new  forms  arising  spontaneously  in  nature  are  for  the  most 

1  Hugo  De  Vries,  Species  and  Varieties,  their  Origin  by  Mutation  [Open  Court 
Publishing  Company,  Chicago]. 


MUTATIONS  115 

part  promptly  exterminated  by  the  rigors  of  natural  selection, 
which  therefore  could  not  have  been  the  chief  agency  in  their 
creation. 

Accordingly  he  conceived  the  idea  of  cultivating  a  few  unstable 
forms  under  conditions  such  as  would  protect  and  preserve  any 
mutations  that  might  arise,  hoping  jn  this  way  to  throw  some 
light  on  the  origin  of  new  types  and  to  determine  whether  in  the 
origin  of  species  natural  selection  works  principally  upon  indi- 
viduals or  upon  types. 

Experiments  with  toadflax 1  (Linaria  vulgaris).  These  experi- 
ments were  designed  to  test  the  origin  of  the  peloric  form.2  The 
toadflax  was  chosen,  first  because  the  peloric  form  is  known  to 
have  arisen  repeatedly,  and  second  because  the  change  involved 
is  slight,  structurally  speaking.  These  two  considerations  gave 
reason  for  the  hope  that  if  the  species  were  put  under  careful 
observation  and  control,  he  (De  Vries)  "might  be  present  at  the 
time  when  nature  produces  another  of  these  rare  changes." 

The  experiments  commenced  in  1886  with  normal  plants  bear- 
ing "one  or  two  peloric  flowers,"  as  is  common  with  most  indi- 
viduals of  this  genus.  The  roots  were  planted  in  the  garden, 
and  flowered  and  seeded  in  1887.  This  second  generation  was 
grown  for  three  years,  producing  in  1 889  3  one,  and  in  1890  two, 
peloric  structures.  The  seeds  of  these  were  saved  and  produced 
the  third  generation  in  1890-1891.  Among  some  thousands  of 
blossoms  in  this  generation  there  was  one  five-spurred  flower. 
This  was  pollinated  by  hand  and  luckily  produced  "  abundant 
fruit,  with  enough  seeds  for  the  entire  culture  of  1892,  and  they 
only  were  sown."  4 

1  De  Vries,  Species  and  Varieties,  etc.,  pp.  464-487. 

2  The  normal  flowers  of  the  toadflax  are  exceedingly  unsymmetrical.    Aside 
from  bearing  a  short  spur,  they  are  described  as  consisting  of  a  "  two-lipped  corolla, 
the  lower  lips  spreading  and  three-lobed,  with  a  base  so  enlarged  as  to  nearly 
close  the  throat."    Plants  bearing  such  unsymmetrical  flowers  as  do  toadflax,  snap- 
dragon, etc.,  are  known  occasionally  to  produce  peloric,  that  is,  symmetrical, 
flowers.    Not  only  that,  but  peloric  varieties  are  not  unknown,  and  these  experi- 
ments were  designed  to  solve  the  manner  of  their  origin. 

3  The  toadflax  is  a  biennial. 

4  Peloric  flowers  of  this  species  are  commonly  sterile,  but  in  any  case  are 
dependent  upon  artificial  fertilization.    They  are  by  nature  ill  adapted  to  preserve 
themselves. 


Il6  VARIATION 

Up  to  this  point  in  the  experiment  each  generation  required 
two  years,  as  the  toadflax  is  a  biennial,  not  blooming  until  the 
second  year.  After  this,  however,  the  seedlings  were  started 
under  glass  and  transplanted  to  the  garden  in  June.  By  this 
means  the  new  plants  were  made  to  produce  flowers  and  seeds 
the  first  year. 

About  twenty  plants  of  this  (fourth)  generation  were  secured, 
and  under  this  treatment  most  of  them  produced  seed  the  first 
year.  Only  one  peloric  flower  was  observed,  however,  in  the 
entire  lot.  The  plant  bearing  this  flower  and  one  other  were 
preserved,  and  all  others  were  destroyed.  These  two  fertilized 
each  other  freely  and  produced  10  cc.  of  seed,  but  no  more 
peloric  flowers  appeared.  It  is  from  this  pair  of  plants,  how- 
ever, that  a  peloric  race  finally  sprung.1 

In  1894  about  fifty  plants  were  in  flower.  There  was  no  rea- 
son for  considering  these  plants  any  more  promising  than  pre- 
vious sowings,  except  that  "  stray  peloric  flowers  were  observed 
in  somewhat  larger  numbers  than  in  previous  generations,  — 
eleven  plants  bearing  one  or  two,  or  even  three,  such  abnor- 
malities." De  Vries  wisely  remarks  that  this  ''could  not  be 
considered  as  a  real  advance,  since  such  plants  may  occur  in 
varying  though  ordinarily  small  numbers  in  every  generation." 

However,  besides  these  eleven  individuals,  each  bearing  one 
or  two  abnormal  flowers,  there  was  a  single  plant  bearing  only 
peloric  flowers.  The  mutation  had  arisen  and  De  Vries  "was 
present  at  the  time." 

This  plant  was  carefully  kept,  all  others  being  destroyed,  and 
the  next  year  it  bloomed  again,  bearing  only  peloric  flowers.  It 
was  true  to  its  type.  In  this  connection  De  Vries  says  : 

Here  we  have  the  first  experimental  mutation  of  a  normal  into  a  peloric 
race.  Two  facts  were  clear  and  simple :  [first]  the  ancestry  was  known 

1  It  has  been  said  that  the  flowers  of  one  plant  are  sterile  to  pollen  from  the 
same  plant.  De  Vries  ascertained  by  careful  experiment  that  this  is  true  in  about 
50  per  cent  of  the  cases,  so  that,  though  a  much  higher  degree  of  fertility  exists 
between  individuals  than  within  the  individual,  absolute  barrenness  between  all 
flowers  of  the  same  plant  cannot  be  asserted.  The  point  is  not  significant  in  the 
present  connection,  but  it  is  important  as  demonstrating  that  fertility  and  sterility 
are  not  always  in  direct  proportion  to  consanguinity,  and  that,  though  close  breed- 
ing may  be  commonly  infertile  in  certain  strains,  it  by  no  means  follows  that  it  is 
always  infertile  even  in  the  same  strain. 


MUTATIONS  1 1 7 

for  over  a  period  of  four  generations.  .  .  .  This  ancestry  was  quite  constant 
as  to  the  peloric  peculiarity,  remaining  true  to  the  wild  type  as  it  occurs 
everywhere  in  any  country,  and  showing  in  no  respect  any  tendency  to  the 
production  of  a  new  variety. 

[Second]  the  mutation  took  place  at  once.  It  was  a  sudden  leap  from 
the  normal  plants  with  very  rare  peloric  flowers  to  a  type  exclusively  peloric. 
The  parents  themselves  had  borne  thousands  of  flowers  during  two  summers, 
and  these  were  inspected  nearly  every  day  in  the  hope  of  finding  some  pelorics 
and  of  saving  their  seed  separately.  Only  one  such  flower  was  seen.  .  .  . 
There  was  simply  no  visible  preparation  for  this  sudden  leap. 

This  leap,  on  the  other  hand  was  full  and  complete.  No  reminiscence  of 
the  former  condition  remained.  Not  a  single  flower  on  the  mutated  plant 
reverted  to  the  previous  type.  .  .  .  The  whole  plant  departed  absolutely 
from  the  old  type  of  its  progenitors. 

The  next  object  was  to  seek  for  other  mutants  from  the  same 
lot  of  seed  l  and  to  compare  their  proportion  with  the  proportion 
coming  true  from  the  seed  of  the  first  mutant. 

Accordingly  De  Vries  planted  his  entire  remaining  stock  of 
seed,  which,  it  will  be  remembered,  was  grown  from  the  pair  of 
plants  one  of  which  bore  a  single  peloric  flower,  but  both  of  which 
were  immediately  descended  from  the  single  five-spurred  flower 
of  the  third  generation. 

From  this  seed  he  grew  about  two  thousand  plants  in  well- 
manured  soil.  About  1750  of  these  bore  flowers,  and  among 
these  sixteen,  or  about  i  per  cent,  were  wholly  peloric.  As  these 
seeds  were  of  the  same  generation  that  produced  the  first  mutant, 
he  concludes  that  the  chance  of  a  peloric  mutant  is  not  over  one 
in  a  hundred. 

De  Vries  next  undertook  to  determine  whether  the  mutation 
would  be  repeated  in  another  generation,  for  up  to  this  point  all 
the  mutants  had  arisen  from  the  same  lot  of  seed.  For  this 
purpose  he  saved  seeds  from  normal  plants  so  isolated  as  to  pre- 
vent crossing  with  peloric  strains.  In  one  instance  he  "  obtained 
two  and  in  another  one  peloric  plant  with  exclusively  many- 
spurred  flowers,"  showing  conclusively  that  mutations  are  itera- 
tive, and  that  the  same  conditions  that  produce  one  mutant 
will  from  time  to  time  produce  others  altogether  similar. 

1  It  will  be  remembered  that  the  original  stock  of  seed  of  this  generation  was 
10  cc.,  but  that  only  enough  had  been  grown  to  produce  fifty  plants,  leaving  a 
quantity  still  on  hand. 


u8  VARIATION 

New  type  persistent.  Next  he  undertook  to  determine  to  what 
extent  these  mutant  pelorics  would  "  breed  true,"  in  order  to 
compare  the  proportion  with  the  previously  ascertained  i  per 
cent.  In  this  he  encountered  difficulty  because  of  the  high 
degree  of  sterility  of  peloric  flowers.  He  had  in  all  some  twenty 
plants,  and  pollinated  artificially  more  than  a  thousand  flowers. 
Of  these  he  says  : 

Not  a  single  one  gave  a  normal  fruit,  but  some  small  and  rudimentary 
capsules  were  produced  bearing  a  few  seeds.  From  these  I  had  119  flower- 
ing plants,  out  of  which  1 06  were  peloric  and  the  remainder  (13)  one-spurred. 
The  great  majority  (some  90  per  cent)  were  thus  shown  to  be  true  to  their 
new  type.  Whether  the  10  per  cent  reverting  ones  were  truly  atavists  or 
whether  they  were  only  vicinists  caused  by  stray  pollen  grains  from  an- 
other culture  cannot  of  course  be  determined  with  sufficient  certitude. 

This  experiment  determines  not  only  the  distinctness  of  the 
new  type  and  the  suddenness  of  its  formation,  but  its  essential 
purity  as  well ;  for  it  bred  true  in  90  per  cent  of  the  cases,  while 
the  probability  of  original  mutation  was  slight,  certainly  not  over 
i  per  cent. 

The  total  lack  of  intermediate  steps  in  the  control  experi- 
ments is  significant.  Their  absence  in  nature  is  not  less  so  (for 
if  they  were  present  as  transition  steps  toward  the  formation  of 
peloric  races,  they  would  certainly  be  discovered,  particularly 
when  we  remember  that  the  species  is  a  perennial),  and  the  con- 
clusion seems  inevitable  that  the  transition  is  abrupt,  and  the 
new  type,  repeatedly  re-formed,  is  without  doubt  to  be  regarded 
as  a  true  mutation. 

The  common  snapdragon,  whose  flowers  are  exceedingly  un- 
symmetrical,  also  has  a  peloric  race.  "  But  the  snapdragon  is 
self-fertile,  and  so  is  its  peloric  variety,"  observes  De  Vries. 
These  mutations  are  therefore  much  more  easily  preserved,  and 
are,  as  we  should  expect,  more  common  than  in  the  toadflax,  — 
so  common  and  so  distinct  as,  without  a  doubt,  to  give  rise  to 
real  hybrids  with  the  old  form. 

What  is  true  of  toadflax  and  snapdragon  is  held  to  be  true  of 
unsymmetrical  flowers  generally ;  namely,  a  strong  tendency  to 
give  rise  from  time  to  time  to  peloric  varieties,  not  by  gradual 
change  of  the  parent  stock  but  by  sudden  offset,  or  mutation. 


MUTATIONS  119 

Experiments  in  the  production  of  double  flowers.1  After 
remarking  that  mutations  occur  as  often  among  cultivated  as 
among  wild  plants,  De  Vries  drops  the  caution  that  in  all  experi- 
mentation of  this  order  hybridism  must  be  carefully  guarded 
against.2  He  observes,  too,  that  white  varieties  seem  compara- 
tively old,  as  they  are  common  in  the  wild  state,  while  double 
flowers  are  rare  in  the  wild  state  and  correspondingly  recent, 
indicating  their  origin  under  cultivation,  and  thus  making  the 
matter  of  doubling  a  favorable  character  with  which  to  conduct 
investigations  upon  mutation. 

In  the  experiments  upon  peloric  toadflax  nothing  new  was 
attempted.  The  object  was  to  repeat  what  nature  was  known 
often  to  have  done,  but  so  to  control  conditions  as  to  "  be  there  " 
when  it  happened  next  time. 

In  this  experiment,  however,  De  Vries  determined  to  attempt 
a  new  mutation,  —  that  is,  to  try  to  secure  double  flowers  where 
they  had  never  been  observed  in  nature.  He  accordingly  chose 
the  corn  marigold  (Chrysanthemum  segetum),  common  in  the 
grain  fields  of  central  Europe,  and  its  cultivated  variety,  grandi- 
florum.  The  number  of  ray  florets  is  variable  in  both,  but  is, 
on  an  average,  thirteen  in  the  wild  and  twenty-one  in  the  culti- 
vated. This  indicated  the  latter  as  the  more  favorable  for  the 
experiment,  and  it  was  therefore  chosen;  but  it  is  far  from  pure, 
for  many  of  its  heads  have  as  few  as  thirteen  rays.  Only  six 
out  of  the  first  lot  of  three  hundred  plants  reached  an  average 
of  twenty-one,  and  these  were  selected  as  the  foundation. 

The  seeds  of  each  of  these  were  sown  separately.  Five  gave 
proof  of  being  still  mixtures  with  the  wild  form  and  were  re- 
jected. The  offspring  of  the  sixth  plant  averaged  twenty-one 
ray  florets,  and  after  counting  some  fifteen  hundred  heads  the 
two  plants  were  selected  whose  secondary  heads  made  the  best 
showing.  The  progeny  of  these  plants  also  averaged  twenty-one, 

1  De  Vries,  Species  and  Varieties,  etc.,  pp.  489-515. 

2  If  a  new  form  is  a  mutant  it  will  "breed  true  "  to  itself  in  the  great  majority 
of  cases  and  perforce  hybridize  with  the  original  stock.    If,  on  the  other  hand,  it 
is  an  ordinary  hybrid,  it  will  not  breed  true,  but  will  observe  the  principle  of 
Mendel's  law  (to  be  discussed  later),  by  which  a  certain  definite  percentage  is  of  the 
original  types.    Thus  it  is  comparatively  easy  to  ascertain  whether  a  new  type  is  the 
product  of  a  single  race  by  mutation  or  of  two  races  by  hybridization. 


1 20  VARIATION 

and  De  Vries  considered  that  the  strain  was  now  pure  and  that 
"  no  further  selection  could  be  of  any  avail." 

One  of  these  two  plants  was  distinguished. by  producing  two 
secondary  heads  with  twenty -two  rays,  whereas  generally  only 
the  terminal  head  reached  so  many  as  twenty-one,  the  other 
retrograding  often  as  low  as  to  thirteen.  This  exceptional  'plant 
was  distinguished  only  by  these  two  secondary  heads.  Its  ter- 
minal head  had  but  twenty-one  rays,  and  the  average  of  all  its 
heads  was  not  exceptionally  high ;  but  no  other  plant  out  of 
hundreds  had  ever  produced  secondary  heads  with  more  than 
twenty-one  rays,  and  it  was  from  this  plant  that  the  double- 
flowering  line  developed  three  years  later. 

This  plant  appeared  in  1896.  Its  seed  was  sown  in  1897. 
The  largest  number  of  rays  in  the  terminal  head  suddenly 
increased  from  twenty-one  to  thirty-four;  next  year  (1898),  to 
forty-eight;  next  (1899),  to  sixty-six;  and  during  this  time  the 
general  average  for  all  the  heads  increased  remarkably.  No 
indication  of  doubling  had,  however,  yet  appeared.  The  im- 
provement was  such  as  follows  selective  breeding  with  fluctuat- 
ing variability,  —  improvement  by  gradual  change  and  without 
mutations. 

Late  in  the  season  (September)  of  this  year  (1899),  how- 
ever, three  secondary  heads  appeared  on  one  plant  with  a  few 
ray  florets  scattered  over  the  disk.  The  mutation  anxiously 
awaited  for  seven  years  had  suddenly  appeared  in  this  small, 
belated  way  toward  the  close  of  the  growing  season,  and  in 
a  manner  that  would  have  escaped  the  attention  of  any  but 
the  most  painstaking  investigator,1  and  that  would  have  invited 
extermination  in  nature. 

This  was  in  1899.  The  heads  were  of  course  pollinated  with 
other  and  inferior  flowers,  but  in  1900  the  highest  number  of 
rays  rose  to  one  hundred,  and  in  1901  reached  two  hundred. 
He  remarks,  "  Such  heads  are  as  completely  double  as  are 

1  The  student  will  note  that  every  flower  of  thousands  of  plants  was  carefully 
examined,  and  that  in  every  case  the  foundation  of  the  mutation  was  in  an  incon- 
spicuous plant,  certain  to  be  overlooked  by  casual  observers.  The  obvious  lesson 
is  that  only  the  most  careful  and  systematic  examination  will  detect  the  founda- 
tion stock,  so  easily  does  it  escape  notice  in  the  general  mass  and  so  readily  is  it 
1  )st  unless  isolated  and  protected. 


MUTATIONS  121 

the  brightest  heads  of  the  most  beautiful  double  commercial 
varieties  of  composites."    He  adds  : 

The  race  has  at  once  become  permanent  and  constant.  Real  atavists  or 
real  reversionists  were  seen  no  more  after  the  first  purification  of  the  race. 
It  has  of  course  a  wide  range  of  fluctuating  variability  (considering  all 
the  heads),  but  the  lower  limit  has  been  worked  up  to  about  thirty-four 
rays,  a  figure  never  reached  by  the  grandiflorum  parent,  from  which  my 
new  variety  is  sharply  separated. 

Unfortunately,  the  best  heads  now  produced  are  sterile,  so 
that  seeds  must  be  secured  from  inferior  stock  and  the  variety 
must  be  propagated  from  slightly  inferior  parentage.  Selection 
has,  therefore,  reached  its  limit,  unless  a  fertile  strain  arises, 
which  is  entirely  possible. 

This  mutation  is  decidedly  new.  It  had  never  been  known, 
nor  had  anything  approaching  it  ever  been  discovered  in  this 
species.  The  only  hope  that  it  might  appear  was  belief  in  the 
principle,  and  the  fact  that  doubling  had  taken  place  in  other 
composite.  Right  royally  was  De  Vries's  prophecy  fulfilled,  and 
again  was  he  "present"  when  it  happened;  not  only  that,  but 
in  this  case  nature  evidently  would  not  have  produced  this 
mutation  without  assistance.  Here  nature  has  accomplished 
with  help  a  work  which  she  was  powerless  to  accomplish  alone, 
but  abundantly  able  to  achieve  with  a  little  assistance. 

Experiments  in  the  production  of  new  species.1  De  Vries  was 
not  content  with  the  simple  production  of  varieties.  He  desired 
to  show  that  the  principle  of  mutation  produces  species  as  well.2 
He  cultivated  many  species  of  wild  plants  in  his  garden,  choos- 
ing wild  in  preference  to  cultivated,  because  he  regarded  the 
latter  as  evidence  of  what  had  recently  taken  place  and,  there- 
fore, not  the  best  stock  for  further  mutation  in  the  near  future. 
In  other  words,  he  desired  to  be  present  before  the  mutation 

1  De  Vries,  Species  and  Varieties,  etc.,  pp.  516-546. 

2  He  distinguishes  sharply  between  varieties  and  species.    The  variety  differs 
from  the  main  stock  in  but  a  single  character,  progressive  or  retrogressive,  while 
the  species  differs  in  all  characters,  some  of  which  are  perhaps  progressive  and 
others  retrogressive.    He  likes  to  distinguish  elementary  species  from  all  other 
types,  as  these  are  in  his  estimation  the  most  stable  forms  in  nature ;  and  when 
any  race  assumes  the  "  mutative  state  "  it  is  likely  to  throw  off,  if  conditions  are 
favorable,  a  large  number  of  new  elementary  species,  each  with  its  new  center  of 
variability. 


I22  VARIATION 

happened,  rather  than  to  enter  just  afterward  and  only  in  time 
to  note  results  with  no  evidence  as  to  methods. 

Of  all  the  hundreds  of  plants  cultivated  he  found  the  evening 
primrose  most  fertile  in  distinct  strains,  both  in  the  wild  and 
hi  the  cultivated  state.  Other  species  gave  rise  to  varieties 
freely,  but  no  other  appeared  to  be  sufficiently  mutable  to  give 
rise  freely  to  what  he  regarded  as  elementary  species. 

Of  all  the  primroses,  CEnothera  Lamarckiana,  commonly  called 
Lamarck's  evening  primrose,  was  the  most  prolific  in  distinct 
forms,  and  accordingly  this  was  chosen  by  De  Vries  for  special 
attention  in  his  experiments.  It  is  described  as  "a  stately 
plant  with  a  stout  stem,  attaining  often  a  height  of  1.6  m.  or 
more.  When  not  crowded,  the  main  stem  is  surrounded  by  a 
large  circle  of  smaller  branches  growing  upward  from  its  base 
so  as  to  form  a  dense  bush.  These  branches  in  their  turn  have 
numerous  lateral  branches.  ...  Contrary  to  their  congeners, 
they  are  dependent  on  visiting  insects  for  pollination." 

Ordinarily  this  primrose  is  a  biennial,  producing  rosettes  in 
the  first  year  and  stems  in  the  second  year.  Both  the  rosettes 
and  the  stems  are  highly  variable  in  nature,  producing  a  num- 
ber of  distinct  races,  some  of  which  show  a  marked  ability  to 
hold  their  own  under  natural  surroundings,  while  others -are  too 
weak  to  endure. 

Many  of  these  De  Vries  regarded  as  new  species.  Experi- 
ments to  determine  this  point  were  commenced  with  stock  dis- 
covered near  Hilversum,  and  three  plans  were  followed  :  first,  to 
transplant  the  apparent  new  species  into  the  garden  whenever 
the  new  race  was  sufficiently  strong;  second,  to  reproduce  weak 
races  by  sowing  seeds  from  "  indifferent "  plants  growing  wild  ; 
third,  to  sow  the  seeds  from  the  introduced  plants.  "  These 
various  methods,"  he  adds,  "have  led  to  the  discovery  of  over 
a  dozen  new  types  never  previously  observed  or  described." 

These  new  plants  are  divisible,  according  to  De  Vries,  into 
five  different  heads  or  "  groups  "  :  (i)  those  that  "  are  evidently 
to  be  considered  as  varieties  in  the  narrower  sense  of  the 
word,"  representing  retrograde  development ;  (2)  "  progressive 
elementary  species "  which  are  "  as  strong  as  the  parent 
species  "  ;  (3)  "  progressive  elementary  species,"  but  weaker  than 


MUTATIONS 


123 


the  parent,  and  "apparently  not  destined  to  be  successful"; 
(4)  certain  forms  that  are  "  organically  incomplete";  (5)  "  in- 
constant forms." 

Group  (i),  retrograde  varieties.  Of  this  class  the  following 
three  forms  were  discovered,  all  produced  in  nature  as  well  as 
in  the  garden : 

O.  l&vifolia,  the  smooth-leaved  variety,  constant  from  seed  and 
never  reverting  except  from  crossing.  As  strong  and  fertile  as 
the  parent. 

O.  brevistylis,  the  short-styled  form.  In  this  the  ovary  is  so 
placed  that  it  is  reached  by  very  few  pollen  tubes.  Thus  while 
the  plant  is  vigorous  it  is  but  indifferently  productive  of  seeds, 
and  as  De  Vries  says  "  many  [capsules]  contained  no  seeds  at 
all ;  from  others  I  have  succeeded  in  saving  only  a  hundred  seeds 
from  thousands  of  capsules."  These  seeds,  however,  reproduce 
the  variety  without  reversions  to  Lamarckiana. 

O.  nanella,  the  dwarf,  "a  most  attractive  little  plant, 
very  short  of  stature,  reaching  often  a  height  of  only  20-30  cm., 
or  less  than  one  fourth  of  that  of  the  parent."  The  flowers 
are  as  large  as  those  of  the  parent ;  the  leaves  are  much 
smaller  and  with  no  reversion  in  seedlings,  even  in  repeated 
and  successive  generations. 

Group  (2),  progressive  elementary  species,  and  vigorous  ;  two 
forms  discovered  : 

O.  gigas,  the  giant,  deserving  its  name  not  from  being  higher 
than  its  parent,  but  because  it  is  "  so  much  stouter  in  all 
respects."  The  stems  are  often  twice  as  thick  as  in  the  parent 
(Lamarckiana),  and  the  "  internodes  are  shorter  and  the  leaves 
more  numerous,  covering  the  stems  with  a  denser  foliage."  The 
flowers  are  larger,  and  the  seed  capsules  are  smaller  and  filled 
with  fewer  but  larger  seeds  than  in  the  parent  plant.  It  has  a 
strong  tendency  to  remain  a  biennial. 

O.  rubrinervis,  the  red-veined  form.  In  this  the  veins  of  the 
leaves  are  distinctly  tinged  with  red  and  the  fruits  are  streaked 
with  red.  The  plants  are  in  many  ways  a  counterpart  of  the 
giant,  except  for  the  red  tinge  and  distinctly  lighter  foliage. 
This  latter  probably  accounts  for  the  marked  tendency  on  the 
part  of  this  form  to  become  an  annual.  Like  the  giant,  this  form 


124 


VARIATION 


is  true  to  type  when  grown  from  the  seed,  and  its  recurrence  is 
far  more  common  than  is  that  of  gigas,  which  is  extremely  rare. 

Group  (3),  progressive  elementary  species,  but  weakly.  Two 
forms  : 

O.  albida,  the  albino,  with  whitish,  narrow  leaves,  "  appar- 
ently incapable  of  producing  sufficient  quantities  of  organic 
food."  The  seedlings  are  exceedingly  delicate,  and  if  left  to 
themselves  will  be  speedily  overgrown  by  their  more  vigorous 
neighbors ;  but  if  transplanted  and  given  the  best  of  care,  they 
make  fairly  vigorous  plants  the  second  year,  comparing  fairly 
well  with  the  parent  stock  but  bearing  fewer  seeds.  They 
come  true  even  to  the  third  generation  and  the  type  remains 
distinct. 

O.  oblonga,  the  narrow-leaved  form.  It  "  may  be  grown  either 
as  an  annual  or  a  biennial.  In  the  first  case  it  is  very  slender 
and  weak,  bearing  only  small  fruits  and  few  seeds.  In  the  alter- 
native case,  however  (biennial),  it  becomes  densely  branched, 
bearing  flowers  on  quite  a  number  of  racemes  and  yielding  a 
full  harvest  of  seeds." 

The  investigator  says  : 

We  have  now  given  the  description  of  seven  new  forms  which  diverge 
in  different  ways  from  the  parent  type.  All  were  absolutely  constant  from 
seed.  Hundreds  or  thousands  of  seedlings  may  have  arisen,  but  they 
always  come  true  and  never  revert  to  the  original  O.  Lamarckiana. 

He  adds  the  remark  that  they  have  inherited  the  condition  of 
mutability  to  some  extent  and  are  evidently  themselves  able  to 
produce  new  forms,  but  that  they  do  so  but  rarely. 

Two  other  forms  belong  to  this  group,  —  O.  semilata  and 
O.  leptocarpa,  —  but  their  characters  do  not  merit  special 
description. 

Group  (4),  forms  organically  incomplete  : 

O.  lata  is  a  pistillate  variety,  wholly  dependent  for  fertiliza- 
tion upon  other  forms,  and  it  had  therefore  no  opportunity  to 
establish  its  type,  which,  however,  freely  appeared.  It  is  a  "low 
plant,"  but  with  "dense  foliage  and  luxuriant  growth."  Its 
presence  can  be  detected  in  the  seedling  by  the  "  broad,  sinuate 
leaves  with  rounded  tips."  Being  pistillate,  it  produces  seed 
only  when  cross  pollinated,  in  which  case  its  characters  are 


MUTATIONS 


125 


transmitted  to  a  portion  only  of  its  offspring,  thus  behaving  like 
hybrids.  Indeed,  he  specifies  that  "  on  the  average  one  fourth 
of  the  offspring  are  lata"  the  others  assuming  the  character  of 
the  pollen  parent,"  —a  strict  example  of  hybridism  between  a 
weaker  and  a  stronger  form,  according  to  Mendel's  law. 

Group  (5),  inconstant  forms  : 

O.  scintillans  is  a  perfectly  fertile  form,  bearing  smooth,  dark- 
green  leaves  with  glistening  surfaces.  It  is  a  natural  dwarf, 
easily  cultivated  as  an  annual.  When  fertilized  with  its  own 
pollen  to  produce  a  "  pure  "  strain,  it  is  found  that  the  seedlings 
all  resemble  the  parent,  but  that  soon  afterward  they  diverge 
into  various  types.  Some  of  these  resemble  the  original  parent 
stock  (Lamarckiana)  and  others  remain  pure,  but  the  proportion 
is  very  variable.  These  might  be  regarded  as  simple  reversions, 
except  that  occasionally  other  types  appear,  especially  oblonga, 
lata,  and  nanella,  the  first  often  constituting  10  per  cent  of  the 
sowings.  It  thus  shows  a  disposition  to  give  rise  to  the  same 
distinct  forms  as  does  its  own  parent,  and  is  thus  regarded  by 
De  Vries  as  being  itself  in  a  "  highly  mutable  state." 

O.  elliptica  is  a  narrow-leaved,  inconstant  type,  exceedingly 
"  difficult  of  cultivation."  Though  fertile  to  its  own  pollen,  it 
"  repeats  its  type  only  in  a  very  small  proportion  of  its  seeds." 

There  are  thus  "  a  dozen  new  types  springing  from  an  original 
form  in  one  restricted  locality  and  seen  to  grow  there,  or  arising 
in  the  garden  from  seeds  collected  from  the  original  locality." 
Most  of  these  types  behave  with  a  constancy  that  ranks  them, 
for  breeding  purposes  at  least,  as  distinct  forms,  good  elementary 
species,  —  new  things  in  the  earth  that  may  be  held  constant  or 
that  may  be  slightly  modified  by  the  exercise  of  selection  among 
the  fluctuations  to  which  all  types  both  old  and  new  are  subject. 
The  experimenter  observes  : 

It  is  most  striking  that  the  various  mutations  of  the  evening  primrose 
display  a  great  degree  of  regularity.  There  is  no  chaos  of  forms,  no  indefi- 
nite varying  in  all  degrees  and  in  all  directions.  On  the  contrary,  it  is  at 
once  evident  that  very  simple  rules  govern  the  whole  phenomena. 

History  of  the  experiment.  In  all  De  Vries  made  four  differ- 
ent series  of  pedigree  cultures  of  the  evening  primrose,  extend- 
ing from  five  to  nine  generations  and  including  thousands  of 


126  VARIATION 

plants.  The  types  that  arose  at  different  times  have  already 
been  described,  but  considerable  interest  and  no  little  profit 
attaches  to  the  details  of  the  experiment,  especially  in  re- 
gard to  the  order  and  manner  of  the  appearance  of  the  new 
types.  The  following  is  abstracted  from  the  experimenter's 
account  of  one  of  these  four  experiments,  running  through 
eight  generations.1 

Beginning  in  the  fall  of  1886  he  took  nine  large  rosettes  of 
O.  Lamarckiana  from  the  field  and  planted  them  in  the  garden. 
The  second  generation  was  sown  in  1888  and  flowered  in  1889. 
The  seed  produced  fifteen  thousand  seedlings,  of  which  ten 
were  divergent  at  once,  —  five  lata  and  five  nanella.  No  inter- 
mediates appeared.  "They  came  into  existence  at  once,"  says 
De  Vries,  "  fully  equipped,  without  preparation  or  intermediate 
steps.  No  series  of  generations,  no  selection,  no  struggle  for 
selection  was  needed.  It  was  a  sudden  leap  into  another  type, 
—  a  sport  in  the  best  acceptation  of  the  word."  2 

The  third  generation  of  ten  thousand  plants  showed  three  lata 
and  three  nanella,  besides  one  rubrinervis. 

Growing  expert  in  detecting  mutants  at  an  early  stage,  he 
discovered  334  young  plants  out  of  14,000  of  the  fourth  gener- 
ation (1895).  This  is  about  2.5  per  cent.  Of  these  176  were 
oblonga,  73  lata,  60  nanella,  15  albida,  8  rubrinervis,  I  scintil- 
lans,  and  I  gigas. 

The  larger  number  and  wider  range  of  mutants  discovered 
this  year  are  to  be  ascribed  to  growing  skill  in  detecting  them 
at  an  early  age.  Manifestly  such  immense  numbers  must  be 
greatly  reduced  at  the  earliest  possible  date,  and  without  doubt 
some  good  forms  were  overlooked  in  the  earlier  generations. 
After  this  (fourth)  generation  the  number  of  seedlings  was 
greatly  reduced,  with  the  effect  of  reducing  the  number  of 
mutants  and  also  the  chances  of  the  rarer  forms  appearing  at 
all  ;  indeed,  gigas  never  appeared  again,  and  scintillans  not  after 

1  De  Vries,  Species  and  Varieties,  etc.,  pp.  549-556. 

2  It  may  occur  to  the  student   to  object  to  the  conclusion  on  the  ground  that 
the  parent  stock  taken  from  the  field  may  not  itself  have  been  pure.    If,  however, 
the  stock  had  been  in  any  sense  hybrid,  the  departures  should  have  been,  accord- 
ing to  Mendel's  law,  more  than  ten ;  but  not  in  this  or  in  later  generations  did 
either  parent  stock  or  mutant  behave  like  a  hybrid  in  this  respect. 


MUTATIONS 


127 


the  sixth  generation.     The  entire  results  of  the  eight  generations 
of  breeding  are  given  in  the  following  table. 

EIGHT  GENERATIONS  OF  A  MUTATING  STRAIN  OF  EVENING  PRIMROSE 
(0.  Lamarckiana) 


GENERA- 
TIONS 

0. 
gigas 

Albida 

Oblonga 

Rubri- 
nervis 

Lamarck- 
iana 

Nanella 

Lata 

Scintil- 
lans 

•I- 

9 

II 

15,000 

5 

5 

III 

I 

10,000 

3 

3 

IV 

I 

15 

I76 

8 

I4,OOO 

60 

73 

I 

V 

25 

J35 

20 

8,000 

•    49 

142 

6 

VI 

II 

29 

3 

1,  800 

9 

5 

i 

VII 

9 

3,000 

ii 

VIII 

5 

i 

1,700 

21 

1 

In  the  opinion  of  the  experimenter  here  are  numbers  enough 
and  types  sufficiently,  distinct  to  warrant  the  enumeration  of 
certain  laws  or  principles  that  appear  to  govern  the  appearance 
of  mutants,  especially  in  the  species  under  observation.  This 
De  Vries  attempts  to  do,  but  without  presuming  to  say  how 
closely  they  may  apply  to  other  strains  of  plants  or  animals. 

Laws  of  mutability  for  evening  primroses.  De  Vries'  experi- 
ments. On  the  basis  of  his  experiments  with  the  evening  prim- 
rose the  investigator  announces  the  following  laws  of  mutability 
as  applying  to  that  species  i1 

1.  "That  new  elementary  species  appear  suddenly,  without 
intermediate  steps."    As  proof  he  points  out  that  no  interme- 
diate forms  appeared  to  fill  the  gaps,  and  that  no  selection  was 
necessary  to  establish  the  type. 

2.  "New  forms  spring  laterally  from  the  main  stem."    "  The 
current  conception  concerning    the   origin  of  species    (or  new 
forms  generally)  assumes  that  species  are  slowly  converted  into 
others.    The  conversion  is  assumed  to  affect  all  the  individuals 
in  the  same  direction  and  in  the  same  degree.  .   .  .  The  birth 

1  De  Vries,  Species  and  Varieties,  etc.,  pp.  558-575.  These  laws,  while 
announced  for  the  evening  primrose,  are  without  doubt  of  wide  if  not  general 
application. 


128  VARIATION 

of  a  new  species  necessarily  seemed  to  involve  the  death  of  the 
old  one,"  at  least  the  old  merged  into  the  new. 

The  experimenter  points  out,  however,  that  through  all  the 
process  of  originating  a  dozen  or  more  distinct  forms,  the  parent 
stock  continued  unchanged,  and  still  constituted  the  principal 
strain  of  all  the  primroses,1  and  from  this  he  deduces  the  law 
that  mutants  are  laterals. 

3.  "  New  elementary  species  attain  their  full   constancy  at 
once."    "  Constancy  is  not  the  result  of  selection  or  of  improve- 
ment.   It  is  a  quality  of  its  own.    It  can  neither  be  constrained 
by  selection  if  it  is  absent  from  the  beginning,  nor  does  it  need 
any  natural  or  artificial  aid  if  it  is  present.". 

De  Vries  remarks  that  scintillans  repeats  its  characters  in 
but  part  of  its  offspring,  and  that  he  has  "  tried  to  deliver  it 
from  this  incompleteness  of  heredity  but  in  vain.  .  .  .  The  insta- 
bility seems  to  be  here  as  permanent  a  quality  as  the  stability 
in  other  instances.  Even  here  no  selection  has  been  adequate 
to  change  the  original  form."  He  regards  it  as  itself  in  a  state 
of  instability. 

4.  "  Some  of  the  new  strains  are  evidently  elementary  species, 
while  others  are  to  be  considered  as  varieties." 

Elementary  species  are  regarded  as  possessed  of  progressive 
characters,  but  varieties  as  differing  from  their  parent  stock  in 
but  a  single  character,  and  that  in  the  way  either  of  an  assump- 
tion or  of  a  loss.  The  elementary  species  is,  therefore,  a  new 
aggregation  of  characters,  while  the  variety  is  simply  the  old 
form  minus  a  single  character.  Whether  this  distinction  holds, 
remains  to  be  determined.  Much  of  the  argument  turns  upon 
what  is  to  be  considered  as  a  character  and  when  it  is  lost.  For 

1  A  natural  corollary  to  this  observation  is  to  remark  upon  the  erroneous  popu- 
lar assumption  that  of  similar  and  contemporaneous  forms  the  more  primitive  are 
necessarily  the  progenitors  of  the  more  nearly  perfect.  For  example,  it  is  hastily 
assumed  that  if  evolution  is  true  then  man  must  be  the  direct  descendant  of  the 
ape.  But  the  ape,  though  very  old,  is  still  an  ape,  and  he  is  not  descending  into 
anything  but  apes.  Though  evidently  developed  from  the  same  original  stock  at 
some  time  and  in  some  way,  whether  by  one  or  by  many  mutations  nobody  knows, 
yet  the  gap  between  us  is  evidently  fixed  and  not  growing  less  or  being  bridged 
at  any  point.  Good  evolution  regards  related  forms  as  connected  by  ties  of  con- 
sanguinity, but  whether  direct,  or,  what  is  more  likely,  indirect,  running  to  some 
extinct  common  ancestor,  only  a  novice  will  attempt  to  say. 


MUTATIONS  129 

example,  is  the  smooth  leaf  or  stem  considered  as  having  lost  a 
character  as  compared  with  its  downy  relative  ? 

5.  "The  same  new  species  are  repeatedly  produced,"  that  is 
to  say,  the  same  new  forms  arise  again  and  again,  showing  that 
the  tendency  to    their    production  is  inherent   and.  persistent. 
"  This  is  a  very  curious  fact,"  remarks  De  Vries.  "  It  embraces 
two  minor  points,  —  the  multitude  of  similar  mutants  in  the 
same  year,  and  the  repetition  thereof  in  succeeding  generations. 
Obviously  there  must  be  some  common  cause.    This  cause  must 
be  assumed  to  lie  dormant  in  the  Lamarckians  of  my  strain,  etc. 
.  .   .  The  germs  of  the  oblonga,  lata,  and  nanella  are  very  irritable 
and  are  ready  to  spring  into  existence  at  the  least  summons,  while 
those  of  gigas,  rubrinervis,  and  scintillans  are  far  more  difficult 
to  arouse."     May  not  the  same  be  true  in  nature  generally,  and 
may  not  the  same  strain  arise  again  and  again,  commonly  fail- 
ing to  persist  because  as  a  rule  all  conditions  are  against  it  ? 

6.  Mutability  is  distinct  from  fluctuating  variability.    Darwin 
regarded  the  new  type  as  built  up  by  the  operation  of  selection 
upon    fluctuating  variability,  establishing  a  new  type    by  the 
gradual  accumulation  of  favorable  variation,  all  others   (inter- 
mediates) being  exterminated.    De  Vries  regards  mutability  as 
distinct  from  fluctuating  variability,  and  considers  that  he  has 
presented  experimental  evidence  to  show  that  it  is  entirely  com- 
petent to  give  rise  to  new  forms  suddenly,  without  intermediates 
and  without  the  aid  of  selection.    He  of  course  believes  that  all 
types,  both  old  and  new,  are  subject  to  fluctuating  variability, 
and  that  through  selection  some  improvement  is  possible,  but  that 
this  is  not  the  sole  or  principal  method  of  securing  new  types. 

7.  "  The  mutations  take  place  in  nearly  all  directions."    Some 
are  larger,  some  are  smaller  than  the  parent ;  some  stronger, 
others  weaker  ;  some  plainer,  others  more  brilliant.    The  species 
is  not,  therefore,  drifting ;  it  is  sending  out  new  types  from  all 
sides. 

SECTION   IV  — AMERICAN   EXPERIENCES 

The  experiments  of  De  Vries  are  strongly  confirmed  by  the 
experience  of  breeders,  especially  in  the  production  of  new  varie- 
ties of  fruits  and  vegetables.  Many  of  these  have  been  so  long 


1 3o 


VARIATION 


under  cultivation  that  nothing  is  known  of  their  origin.  Of  others, 
on  the  contrary,  the  life  history  is  well  known. 

When  Europeans  peopled  America  they  naturally  brought 
with  them  their  fruits,  their  vegetables,  their  grains,  their  grasses, 
and  their  domestic  animals.  The  new  country  was  rich  in  native 
species,  both  plant  and  animal,  but  the  European  species  had 
the  advantage  of  being  better  known  and  better  adapted  to  the 
special  needs  of  man.  Accordingly,  wherever  the  introduced 
varieties  succeeded,  the  corresponding  native  types  were  neg- 
lected ;  but  when  the  European  varieties  failed,  then  the  natives 
were  developed.  It  is  from  this  latter  class  that  some  important 
observations  may  be  made.1 

The  gooseberry.2  The  large  English  gooseberry  was  too  tender 
for  the  American  climate,  and  withal  was  exceedingly  liable  to 
mildew.  Native  varieties  flourished  widely  in  the  forests.  Unfor- 
tunately the  varieties  bearing  the  largest  berries  were  exceedingly 
thorny,  both  on  bush  and  fruit.  Side  by  side,  however,  with  these 
prickly  sorts  were  smooth  varieties,  free  from  "  prickers"  both  on 
fruit  and  bush.  These  were  freely  transplanted  to  the  gardens 
of  the  pioneers  and  furnished  an  acceptable  fruit.3  In  good  time 
they  developed  improved  sorts,  —  first  the  Houghton,  a  seed- 
ling originated  by  Abel  Houghton  of  Lynn,  Massachusetts,  some- 
time in  the  early  forties.  Then  came  the  Downing,  a  seedling  of 
the  Houghton,  first  described  in  1853,  the  fruit  of  which  is  said 
to  be  "  the  largest  yet  known,  being  about  twice  the  size  of  the 
Houghton's  seedling,  its  parent ;  it  is  pale  or  light  green,  without 
any  blush,  and  smooth.  The  skin  is  very  thin  and  the  fruit  as 
delicate  and  tender  as  any  European  gooseberry  on  its  native 
soil.  The  flavor  and  aroma  are  perfect." 

Bailey  observes  in  this  connection,  "  This  berry,  now  known 
as  the  Downing,  is  the  standard  of  excellence  in  American 
gooseberries,  and  is  probably  grown  more  extensively  than  all 
other  varieties  combined  ;  and  yet  it  is  only  two  removes  from 
the  wild  species." 

1  L.  H.  Bailey,  Evolution  of  our  Native  Fruits   [The  Macmillan  Company, 
New  York]. 

2  Ibid.  pp.  389-399- 

8  The  writer  remembers  very  well  as  a  boy  searching  the  woods,  and  espe- 
cially the  swamps,  of  Michigan  for  these  smooth  varieties  for  transplanting. 


MUTATIONS 

Is  not  this  a  natural  mutation  in  the  truest  sense  of  the  term  ? 
If  not,  then  it  is  merely  a  question  of  terminology  and  definition. 
The  fact  remains  that  it  arose  suddenly,  a  distinct  type,  and 
remains  true  with  no  characteristics  of  a  hybrid.  We  need  a  term 
for  this  sort  of  thing  which  is  occasionally  occurring  everywhere 
in  nature,  in  our  gardens  and  in  our  herds,  and  I  know  of  none 
better  then  the  one  already  in  use  —  mutation. 

The  strawberry.1  The  wild  strawberry  grew  everywhere  in 
northern  North  America.  There  were  not  only  many  distinct 
types  of  the  red,  but,  like  the  native  raspberry  and  the  blackberry, 
it  had  everywhere  its  albino  race.  Good  progress  had  been  made 
in  the  cultivation  of  the  native  strawberries,  and  without  doubt 
good  varieties  would  in  time  have  developed  ;  but  the  introduction 
of  the  Chilean  berry  (the  parent  of  most  present  varieties)  seems 
to  have  put  a  stop  to  this.  The  most  promising  of  all  native 
strains  was  the  Fragaria  Chiloensis,  a  native  to  Oregon  and  the 
Pacific  coast  ;  but,  as  Bailey  observes,  "  the  garden  progeny  of 
its  South  American  branch  is  already  so  good  that  there  is  little 
reason  for  returning  to  the  wild  for  a  new  start."  Here  is  a  curi- 
ous instance  of  the  successive  supplanting  of  varieties.  European 
sorts  were  vanquished  by  developments  of  New  England  natives. 
Then  the  wild  type  of  Oregon  came  into  the  struggle  and 
threatened  to  supplant  them  both,  for  it  was  full  of  promise. 
But  its  prosperity  was  its  own  defeat,  for  its  own  Chilean 
brother  has  now  supplanted  everything  in  that  it  is  the  stock 
which  is  furnishing  our  improved  varieties.  Any  student  of  this 
subject  will  recognize  the  comparative  readiness  with  which  these 
new  types  spring  up. 

The  blackberry.2  The  blackberry  grows  wild  both  in  America 
and  in  Europe,  but  is  said  to  be  cultivated  only  in  North  America. 
It  is  not  more  than  fifty  years  since  improved  varieties  were 
introduced,  and  its  real  cultivation  dates*  only  from  about  1875. 

There  are  two  principal  types  of  the  wild  blackberry  growing 
in  the  northern  United  States:  (i)  the  "high  bush,"  long  and 
luscious,  loving  the  shade,  represented  in  its  cultivated  types, 
according  to  Bailey,  by  the  Taylor  and  the  Ancient  Briton; 

1  L.  H.  Bailey,  Evolution  of  our  Native  Fruits,  pp.  424-432. 

2  Ibid.  pp.  298-330. 


132 


VARIATION 


(2)  a  smaller  variety  growing  in  sunny,  open  places  and  bearing 
small,  round,  loose-grained  fruits,  ripening  late  and  exceedingly 
sour.  This  type  is  represented  in  cultivation  by  Lawton, 
Kittatinny,  Snyder,  Agawam,  Erie,  and  others.  Neither  of  these 
yielded  readily  to  cultivation  and  restraint,  and  this  fact  served 
in  an  early  day  to  earn  an  evil  reputation  for  what  Professor 
Card  calls  this  "  gypsy  of  the  fruits."  Nevertheless,  they  yielded 
to  persistent  efforts,  and  have  given  rise,  as  Bailey  puts  it,  "  to  a 
host  of  varieties  .  .  .  very  many  of  them  wildings,  or  chance 
bushes  found  in  fence  rows." 

The  first-named  variety  was  the  Dorchester,  introduced  about 
1841.  Its  exact  origin  is  unknown,  though  its  originator  (prob- 
ably Captain  Lovett)  is  known  to  have  transplanted  wild  plants 
for  many  successive  years.  Whether  this  first  civilized  gypsy 
was  a  sport  or  simply  a  strain  improved  by  selection  is  not  now 
capable  of  proof,  and  yet  its  constancy  is  good  presumptive 
evidence. 

Wilson's  Early  was  known  in  1854,  the  Holcomb  in  1855,  and 
in  1857  the  Lawton  (first  called  New  Rochelle)  was  introduced, 
being  at  once  declared  superior  to  the  Dorchester.  Of  these  the 
Wilson  was  "discovered  in  the  wild  about  1854  by  John  Wilson 
of  Burlington,  New  Jersey";  and  the  Lawton,  formerly  New 
Rochelle,  "  was  found  in  the  town  of  New  Rochelle,  New  York, 
by  Lewis  A.  Secor."  These  two  strains  have  given  rise  to 
numerous  distinct  modern  varieties.  The  "loose-cluster"  strains 
are  regarded  by  horticulturists  as  the  descendants  of  the  Wilson. 
The  origin  of  certain  other  varieties  seems  to  be  as  follows : 

In  1870  Mr.  William  Parry,  of  New  Jersey,  "selected  a 
healthy  young  Dorchester  and  planted  it  in  the  same  hill  with  a 
strong,  healthy  Wilson's  Early  (for  breeders),  located  far  away 
from  any  other  blackberries."1  In  1875  the  seed  from  some  of 
the  largest  berries  growing  on  the  Wilson  were  planted.  One 
plant  only  was  regarded  as  valuable,  and  all  others  were  destroyed. 
This  new  strain  was  named  Wilson  Junior.  The  fruit' was  "  large, 
early,  and  very  fine,"  and  so  prolific  that  in  1884  "one  acre 
yielded  1 10^-  bushels  of  fruit,  by  the  side  of  five  acres  of  Wilson's 
Early  in  the  same  field,  with  the  same  culture,  which  averaged 

1  Bailey,  Evolution  of  our  Cultivated  Fruits,  p.  316. 


MUTATIONS 

but  53  bushels."  The  Eureka  was  produced  in  exactly  the  same 
way  in  1877.  In  1879  Rioter  and  Farmer's  Glory  were  also 
produced  from  berries  growing  on  the  Wilson,  and  Gold  Dust 
and  Primordian  from  berries  growing  on  the  Dorchester.  The 
Gold  Dust  was  remarkable  for  the  fact  that  its  entire  crop  ripened 
within  a  period  of  four  days.  It  was  thus  distinct  from  all  other 
blackberries  in  at  least  one  important  character. 

The  Sterling  Thornless  arose  as  a  chance  seedling  of  the 
Wilson  on  thp  farm  of  John  Sterling  at  Benton  Harbor,  Michigan. 
It  is,  as  its  name  indicates,  destitute  of  thorns,  and  is  a  distinct 
mutation,  to  be  carefully  distinguished  from  other  strains  of 
thornless  blackberries,  which,  according  to  Bailey,  are  "  specific- 
ally distinct  from  the  common  bush  blackberry." 

Plums.1  According  to  Bailey  not  a  single  commercial  variety 
of  plum  has  ever  originated  from  the  native  stock  of  New  Eng- 
land, New  York,  Pennsylvania,  or  Michigan.  This  is  partly 
because  the  European  sorts  thrive  well  and  partly  because  the 
natives  of  this  region  "  are  less  prolific  of  large-fruited  forms  than 
those  farther  west." 

Some  excellent  varieties  have  arisen,  however,  from  native 
stock  elsewhere.  The  Miner  was  produced  from  seed  of  native 
stock  planted  in  1814  by  William  Dodd  in  Knox  County, 
Tennessee.  The  Robinson  was  a  seedling  from  North  Carolina 
stock.  Wayland  "  came  up  in  a  plum  thicket  in  the  garden 
of  Professor  H.  B.  Wayland  of  Cadiz,  Kentucky,"  and  was 
introduced  about  1876.  The  Missouri  apricot  was  found  wild 
in  Missouri.  The  Golden  Beauty  was  found  in  the  same  way 
in  Texas,  the  Pottawattamie  in  Tennessee,  and  the  Newman  in 
Kentucky. 

The  Wolf  originated  from  seed  gathered  from  wild  trees  in 
Iowa.  The  Rollingstone  was  found  on  the  bank  of  Rolling- 
stone  Creek,  Minnesota,  and  the  Quaker  was  found  wild  in  Iowa. 
Literally  scores  of  well-defined  varieties  have  arisen  from  native 
stock.  It  would  be  too  much  to  say  that  none  of  these  are  hybrids. 
Undoubtedly  many  of  them  are  the  product  of  crossing,  but  this 
origin  cannot  be  consistently  claimed  from  chance  seedlings 
found  in  a  thicket  of  ordinary  wild  stock.  Mutation,  whatever 

1  Bailey,  Evolution  of  our  Native  Fruits,  pp.  170-226. 


!  34  VARIATION 

it  is,  must  be  credited  with  having  produced  many  new  forms 
spontaneously. 

Grapes.1  "  North  America  is  a  natural  vineyard,"  says  Bailey, 
and  yet  with  the  most  skillful  and  persistent  attempts  to  culti- 
vate the  European  varieties  for  wine  making,  they  have  not  suc- 
ceeded. Under  these  circumstances  nothing  is  more  natural 
than  that  valuable  native  varieties  should  arise,  providing  the 
capacity  was  inherent  in  the  species. 

John  Adlum  wrote,  about  1823,  "The  way  is  to  drop  most 
kinds  of  foreign  vines  at  once  and  seek  for  the  best  kinds  of  our 
largest  native  grapes."  He  is  to  be  remembered  for  the  intro- 
duction of  the  famous  Catawba,  which  was  "  found  wild  in  the 
woods  of  Buncombe  County  in  extreme  western  North  Carolina 
in  1802." 

The  Catawba  is,  therefore,  almost  certainly  a  sport  of  the 
wild  grape  growing  in  profusion  in  that  region.  In  1843  came 
the  Diana,  a  seedling  of  the  Catawba. 

In  1840  Mr.  E.  W.  Bull  bought  a  house  in  Concord.  Some 
seedlings  of  wild  grapes  sprang  up  about  it,  one  of  which  fruited 
in  1843.  It  was  so  excellent  in  quality  that  all  others  were 
destroyed  and  the  new  variety  was  named  the  Concord.  This 
seedling  has  since  given  us  the  Worden,  Moore  Early,  Pockling- 
ton,  Eaton,  and  Rockland,  of  which  the  first  has  long  been 
famous.  The  Concord,  itself  a  mutant,  seems  to  have  been 
peculiarly  rich  in  possibilities  for  still  other  races. 

"  In  the  year  1821  Honorable  Hugh  White,  then  in  the  junior 
class  in  Hamilton  College,  New  York,  planted  a  seedling  vine 
in  the  grounds  of  Professor  Noyes,  on  College  Hill,  which  still 
remains,  and  is  the  original  Clinton." 

These  are  only  a  few  of  the  many  varieties  of  grape  of  Ameri- 
can origin,  tracing  directly  to  wild  native  stock. 

Lost  possibilities.  Had  other  domesticated  plants  and  animals 
brought  from  Europe  succeeded  less  admirably,  what  enrichment 
might  have  come  through  the  native  flora  and  fauna  of  America ! 

The  prairie  chicken  would  have  been  improved  if  the  domestic 
hen  had  not  succeeded.  The  turkey  was  a  new  thing  and  was 
therefore  seized  upon.  The  buffalo  would  not  now  be  extinct 

1  Bailey,  Evolution  of  our  Native  Fruits,  pp.  1-126. 


MUTATIONS  135 

if  cattle  had  acclimated  less  successfully.  Native  grains  other 
than  maize  would  have  been  developed  had  it  not  been  for  this 
competition,  and  native  grasses  have  not  lived  up  to  their  possi- 
bilities. This  is  through  no  fault  of  theirs,  though  we  still  lack 
4 'the  best  American  grass." 

SECTION  V  — ECONOMIC  SIGNIFICANCE  OF  MUTATIONS 

Because  of  the  waywardness  of  sports,  —  the  impossibility 
of  predicting  their  appearance,  the  readiness  with  which  they 
disappear  when  interbred  with  the  parent  stock,  and  their  very 
frequent  inability  to  reproduce  at  all,  —  because  of  all  these  con- 
siderations it  has  become  fashionable  to  declare  sports  in  general 
to  be  of  slight  economic  importance  and  unworthy  the  breeder's 
serious  attention.  The  only  course  left  open  for  improvement  is, 
therefore,  the  slow  one  of  gradual  accumulation  through  selec- 
tion of  minute  but  favorable  variations,  according  to  the  theory 
of  Darwin. 

The  best  of  evidence  exists,  however,  for  believing  that  this 
is  a  hasty  and  unwarranted  conclusion,  and  that  many,  if  not 
indeed  most,  of  our  really  valuable  new  types  have  arisen  sud- 
denly as  mutations  and  not  gradually  through  infinitesimal  differ- 
ences, as  is  commonly  supposed.  The  experiments  of  DeVries 
and  the  American  varieties  of  fruits  both  come  near  enough  to 
the  origin  of  types  to  more  than  warrant  this  view  of  the  situa- 
tion and  to  afford  ground  for  the  greatest  hope  that  unsuspected 
possibilities  still  exist  in  many  if  not  most  domesticated  species, 
—  possibilities  of  spontaneously  giving  off  varieties  representing 
essentially  new  combinations  of  the  characters  of  the  species  and 
consequently  possessed  of  different  and  perhaps  enhanced  eco- 
nomic value.  The  work  of  Luther  Burbank1  and  of  our  commer- 
cial seedsmen  add  confirmation  to  this  hope,  which,  if  well 
founded,  promises  new  methods  in  breeding  and  vastly  increased 
possibilities  for  improvement. 

The  small  numbers  involved  in  animal  breeding  reduce  enor- 
mously the  chances  of  mutations  appearing  ;  and  yet  nearly  every 

1  W.  S.  Hanvood,  in  The  Century  Magazine,  March  and  April,  1905;  also  New 
Creations  in  Plant  Life  [The  Macmillan  Company,  1906]. 


!  36  VARIATION 

species  has  thrown  off  its  albino  variety,  which  in  most  cases  is 
easily  propagated.  Hornless  cattle  occasionally  appear  in  nearly 
all  breeds,  and  the  type  is  comparatively  easy  of  preservation. 
It  is  more  than  likely  that  the  different  types  in  the  larger 
breeds,  which  breeders  find  so  difficult  to  break  up,  are  in 
reality  quite  distinct. 

In  future  chapters  dealing  with  the  measurements  of  variation 
and  the  statistics  of  heredity  in  general,  it  will  appear  that  even 
fixed  types  afford  sufficient  deviation  to  keep  a  breeder  busy 
with  selection ;  in  other  words,  that  the  animal  breeder  dealing, 
as  he  is,  with  small  numbers  will  always  find  sufficient  variation 
to  lead  him  to  suppose  that  he  is  getting  results  of  his  selection 
even  when  he  has  not  shifted  the  center  of  variation  the  slight- 
est. Much  that  passes  for  breeding  is  nothing  more  than  this 
ineffectual  multiplication,  and  it  is  not  too  much  to  say  that 
hundreds  of  breeders  and  thousands  of  animals  have  lived  and 
died  without  affecting  the  breed  in  the  slightest. 

The  writer  is  strongly  of  the  opinion  that  while  selection  is  a 
powerful  agent  for  "  shaping  up  "  and  "  finishing  off  "  a  fairly 
acceptable  type,  and  while  it  is  the  only  means  of  deciding 
what  shall  live  and  what  shall  disappear,  yet  much  of  the  real 
advance  in  both  animal  and  plant  breeding  is  likely  to  come 
through  distinct  offsets  which  are  now  called  mutations,  and 
which  in  Darwin's  time  and  until  recently  were  erroneously,  if 
not  reproachfully,  denominated  "  sports." 


SECTION   VI  —  BIOLOGICAL  SIGNIFICANCE  OF 
MUTATIONS 

Too  much  mystery  has  surrounded  this  matter  of  sports, 
and  there  has  been  a  too  ready  tendency  to  evoke  the  aid  of 
latent  characters  to  explain  this  and  almost  every  other  unusual 
phase  of  evolution. 

In  truth,  there  is  no  more  mystery  about  mutations  than 
about  heredity  in  general,  which  is  a  complication  of  mysteries. 
It  is  not  a  question  of  latency  but  of  relative  prominence  of 
characters,  of  the  possible  loss  of  a  racial  peculiarity,  or,  what 


MUTATIONS  137 

is  more  likely,  a  new  combination  of  the  elements  out  of  which 
characters  are  made  up. 

Every  new  being  is  the  result  of  a  new  combination  of  racial 
faculties  transmitted  from  two  family  lines,  possibly  differing 
in  essential  particulars.  This  new  combination  is  certain  to 
throw  some  characters  into  prominence  and  others  into  the 
background,  and  results  occasionally  in  strikingly  new  effects. 
This  is  usually  the  case  in  hybridization,  but  it  follows  in  less 
degree  in  ordinary  reproduction,  which  differs  from  hybridiza- 
tion more  in  degree  than  in  kind. 

Again,  many  characters,  though  exceedingly  noticeable,  rest 
after  all  upon  a  comparatively  simple  basis.  Such,  for  example, 
is  pubescence  in  plants,  which  depends  upon  the  activity  or 
non-activity  of  a  few  cells  in  developing  a  hairy  growth.  Nearly 
all  species  present  both  forms,  — the  one  in  which  the  character 
is  present,  and  its  opposite  in  which  it  fails  to  develop.  Simi- 
larly, almost  any  character  may  fail,  giving  rise  to  a  distinctly 
new  creation.  If  the  failure  is  not  at  a  vital  point  it  may  be 
transmitted,  in  which  case  a  new  type  has  arisen. 

The  origin  of  a  new  type  by  the  addition  of  a  character  is, 
biologically  considered,  much  more  complicated  and  difficult  of 
understanding;  yet  even  this  is  not  beyond  some  degree  of 
comprehension.  The  probability  is  that  what  we  call  racial 
characters  are  less  complicated  than  we  may  at  first  suppose. 
The  unlearned  savage  could  scarcely  believe  that  the  almost 
infinite  variety  of  colors  of  natural  objects  are  due  to  different 
combinations  of  very  few  primaries.  The  effects  produced  by 
three-color  printing  are  almost  beyond  belief,  yet  we  are  fully 
advised  as  to  the  real  basis  for  all  these  variations ;  while  the 
effects  are  striking,  the  means  are  simple. 

So  it  is,  we  may  imagine,  in  the  ultimate  make-up  of  what  we 
call  racial  characters  :  their  elements  are  doubtless  fewer  than 
we  have  supposed,  and  the  possibilities  of  their  combinations 
and  recombinations  are  greater  than  we  have  hitherto  imagined. 
Whether  all  possible  combinations  of  these  elements  actually 
take  place  we  do  not  know,  but  all  facts  go  to  show  that  they 
occur  in  great  variety,  the  most  striking  and  permanent  of  which 
we  call  mutants. 


138 


VARIATION 


If  a  new  race  is  produced  by  hybridization,  then  a  new  com- 
bination of  characters  has  been  effected,  and  it  is  fair  to  assume 
that  the  combination  is  richer  in  possibilities  and  possesses  a 
larger  number  of  characters  than  did  either  parent.  Mutation 
teaches  that  new  assortments  of  characters  may  take  place,  in 
some  cases  at  least,  without  hybridizing. 

If  a  racial  character,  as  color  or  hairiness,  is  lost,  we  recognize 
the  new  type  and  name  it  as  a  new  creation.  It  may  be  more 
valuable  to  us  than  its  parent,  but  it  must  be  recognized  biolog- 
ically as  having  lost  something  to  which  it  was  racially  entitled. 

Again,  if  all  normal  characters  acquire  an  unusual  develop- 
ment, relatively  or  absolutely,  as  in  giants,  or  if  their  develop- 
ment is  abnormally  arrested,  as  in  dwarfs,  we  again  recognize 
the  new  departure,  and  it  is  a  good  mutation. 

Still  again,  if  certain  characters  only  undergo  change  in  devel- 
opment, while  others  remain  normal,  then  relative  values  are 
changed,  the  effect  is  altered,  and  we  recognize  a  different  type. 
This,  too,  is  a  good  mutation,  provided  the  new  relation  persists. 
All  these  changes  can  be  worked  with  the  normal  characters 
of  the  race,  without  the  introduction  of  new  characters  or  even 
the  supposititious  aid  of  latent  characters.  Soberly  considered, 
these  changes  are  none  other  than  the  student  of  biology  would 
expect,  unless  indeed  racial  characters  are  bound  together  much 
more  rigidly  than  present  evidence  would  lead  us  to  suspect. 

Summary.  Not  all  variations  are  continuous  and  connected 
with  the  type  by  insensible  differences.  Some  deviations  are  dis- 
continuous, with  a  tendency  for  future  variations  not  reverting  to 
the  main  type  but  clustering  about  a  new  center  of  variability,  thus 
setting  up  a  new  type.  Such  a  deviation  is  called  a  mutant,  and 
new  strains  may  arise  in  this  manner,  as  well  as  by  the  slower 
Darwinian  method  of  heterogeneous  variation,  out  of  which  new 
types  are  established  by  the  slow  process  of  selection. 

Both  the  experience  of  breeders  —  especially  with  new  varie- 
ties in  America — and  numerous  instances  of  experimental  evi- 
dence show  conclusively  that  new  strains  not  only  may,  but  in 
actual  practice  do,  originate  in  this  manner,  suddenly  and  com- 
pletely, without  any  apparent  preparation  and  with  little  tendency 
to  revert  to  the  original  or  main  type,  which  continues  as  before 


MUTATIONS 


139 


Mutants,  like  their  parent  types,  are  subject  to  fluctuating 
variability,  which  is  a  necessary  law  of  reproduction,  and  they 
may  be  improved  —  that  is,  shaped  up  —  by  judicious  selec- 
tion, but  their  principal  characters  and  main  trend  were  fixed 
when  the  type  arose. 

ADDITIONAL  REFERENCES 

ALBINISM.  (A  critical  study  of  its  causes.)  By  E.  Pantanelli.  Experiment 
Station  Record,  XV,  55. 

ATAVIC  MUTATION  OF  THE  TOMATO.  By  C.  A.  White.  Science,  XVII, 
76-78,  234-235. 

ATAVISM  IN  THE  POTATO.  By  S.  Rhodin.  Experiment  Station  Record, 
XI,  710. 

DETERMINATE  MUTATIONS.  (De  Vries  and  others  quoted.)  By  M.  M. 
Metcalf.  Science,  XXI,  355-356. 

EVOLUTION  AND  ADAPTATION.  By  T.  H.  Morgan.  Science,  XIX, 
221-225. 

EVOLUTION  WITHOUT  MUTATION.   By  C.  B.  Davenport.   Science,  XIX,  215. 

INHERITANCE  OF  MONSTROSITIES.  (Experiments  of  twelve  years.)  By 
Hugo  De  Vries.  Experiment  Station  Record,  XI,  546. 

MUTATION  AND  SELECTION.  (What  causes  mutations  ?  Are  they  all  in 
one  direction?)  By  M.  M.  Metcalf.  Science,  XIX,  75-76. 

MUTATION  IN  THE  TOMATO.    By  C.  A.  White.    Science,  XIV,  841-844. 

MUTATION  .THEORY.  (A  review  of  Species  and  Varieties.)  By  C.  B.  Daven- 
port. Science,  XXII,  369-372. 

MUTATION  THEORY  OF  DE  VRIES.  (Twenty-eight  lectures  by  the  author 
at  the  University  of  California,  1904.)  Experiment  Station  Record, 
XVI,  745- 

MUTATION  THEORY  OF  DE  VRIES.  By  D.  T.  McDougal.  Experiment 
Station  Record,  XIII,  324-619;  XIV,  226,  526. 

MUTATION  THEORY  OF  ORGANIC  EVOLUTION.  (A  brief  but  pointed  sur- 
vey of  the  subject.)  By  W.  E.  Castle  of  Harvard  University.  Science, 
XXI,  521-543;  from  standpoint  of  animal  breeding,  521-524;  from 
standpoint  of  cytology,  525-528. 

MUTATIONS  IN  PLANTS.  By  D.  T.  McDougal.  American  Naturalist, 
XXXVII,  737-770;  also  in  Experiment  Station  Record,  XVI,  23. 

ORIGIN  OF  SPECIES.    By  Hugo  De  Vries.    Science,  XV,  721-729. 

ORIGIN  OF  SPECIES  THROUGH  SELECTION  CONTRASTED  WITH  THEIR 
ORIGIN  THROUGH  APPEARANCE  OF  DEFINITE  VARIETIES.  By  T.  H. 
Morgan.  Popular  Science  Monthly,  LXVII,  54-66. 

PREPOTENCY  OF  INDIVIDUALS  WITH  ABNORMAL  VARIATION  OR  MUTA- 
TION. (A  study  of  cats  with  extra  toes.)  By  H.  B.  Torrey.  Science, 
XVI,  554-555- 


1 40  VARIATION 

SOME  CAUSES  OF  SALTATORY  VARIATION.  By  C.  H.  Eigenmann.  Pro- 
ceedings of  the  American  Association  for  the  Advancement  of  Science, 
1900,  XLIX,  207. 

SPORTS.  (Author  concludes  there  are  other  laws  than  Mendel's  and  Galton's.) 
By  C.  B.  Davenport.  Science,  XIX,  151  ;  also  in  Experiment  Station 
Record,  XV,  753. 

SPORTS  ON  GRAPEVINES.  By  J.  C.  Talback.  Experiment  Station  Record 
XV,  478- 

SPORTS  ;  THE  PEACH-NECTARINE.  Journal  of  the  Royal  Horticultural  So- 
ciety, XXVI,  596-598;  also  in  Experiment  Station  Record,  XIV,  45. 

THE  MUTATION  OF  LYCOPERSICUM.  By  C.  A.  White.  Popular  Science 
Monthly,  LXVII,  151-162. 

THE  MUTATION  THEORY.  (A  defense.)  By  Thomas  L.  Casey.  Science, 
XXII,  307-309. 

THE  ORIGIN  OF  A  WHITE  BLACKBERRY.  By  Luther  Burbank.  Exper- 
iment Station  Record,  XIV,  1071. 

THEORY  OF  MUTATIONS.  By  A.  A.  W.  Hubrecht.  Popular  Science 
Monthly,  LXV,  205-223. 


PART  II — CAUSES  OF  VARIATION 


INTRODUCTION 

Variation  is  at  once  the  most  promising  agent  for  improve- 
ment and  the  most  powerful  and  subtle  force  for  undermining 
and  destroying  what  has  already  been  attained.  Because  of  this 
and  with  a  view  to  their  possible  control,  the  breeder  is  especially 
interested  in  the  causes  that  lead  to  deviation  in  plant  or  animal 
characters. 

It  is  said  that  it  is  yet  too  early  to  inquire  into  the  causes  of 
variation,  because  our  stock  of  accurate  knowledge  is  too  limited 
to  permit  a  settlement  of  this  most  complicated  question.  That 
.the  matter  cannot  be  fully  settled  in  the  present  state  of  knowl- 
edge is  beyond  question,  but  the  writer  does  not  share  the  opin- 
ion that  discussion  at  this  stage  of  proceedings  is  unprofitable. 

The  student  of  general  evolution  may  well  assume  the  role  of 
a  curious  but  disinterested  observer,  note  what  passes  before 
his  eyes,  and  take  his  choice  as  to  the  questions  that  shall 
engage  his  attention.  Not  so  with  the  farmer  and  breeder.  His 
funds  are  tied  up  in  his  animals  and  his  plants.  He  is  breeding 
them  not  for  amusement  but  for  profit,  and  he  is  interested  in 
results  not  thousands  of  years  hence  but  in  those  that  may  be 
confidently  expected  within  the  limits  of  a  lifetime. 

He  above  all  men,  therefore,  is  interested  in  variation  and 
the  causes  that  induce  it ;  and  we  are  bound  in  his  interest  to 
study  the  question  assiduously,  to  determine  what  is  known 
and  what  is  not  known  on  this  most  important  point,  and  to 
indicate  as  well  as  we  are  able  the  direction  from  which  further 
light  may  be  expected.  To  this  end  everything  is  important 
that  is  connected  with  variability  in  a  causative  way,  whether 
its  effect  is  upon  either  the  form  or  the  function  of  living 
matter. 

141 


CHAPTER  VII 

THE  MECHANISM  OF  DEVELOPMENT  AND  DIFFERENTIATION 

Before  specific  inquiries  can  be  profitably  made  into  the  causes 
of  variation  it  is  necessary  to  become  fairly  familiar  with  what 
is  known  of  the  essential  constitution  of  living  matter  and  of  its 
manner  of  growth  and  differentiation. 

After  attention  has  been  bestowed  for  a  time  upon  these  con- 
siderations, it  will  be  evident  to  the  student  that  here,  in  the 
inner  workings  of  living  matter,  are  fundamental  causes  of  pro- 
found variations,  even  in  protoplasm  seemingly  the  most  stable. 

SECTION  I  — PROTOPLASM  THE  PHYSICAL  BASIS 
OF  LIFE 

Protoplasm  is  a  general  name  for  all  matter  that  is  endowed 
with  life,  but  the  student  must  never  forget  that  the  biologist, 
like  the  chemist,  is  dealing  with  matter  composed  of  well-known 
chemical  elements  united  in  definite  proportions.  The  known 
differences  between  living  and  non-living  matter  are,  for  our 
purposes,  the  following : 

1.  Living  matter  is  endowed  with  a  mysterious  force  called 
life. 

2.  Matter  so  endowed  has  a  much  more  complicated  chemical 
composition  than  has  non-living  matter,  or  than  can  be  main- 
tained after  the  life  principle  has  departed.    Living  matter  at 
death,  therefore,  breaks  up   (or  down)  into  ordinary  chemical 
compounds.     The   true   constitution   of    living  matter  cannot, 
therefore,  be  determined  by  any  known  methods  of  analysis, 
which  reveal  only  the  elements  involved  but  not  their  exact 
relations  during  life. 

3.  Matter  endowed  with  life  is  able  to  appropriate  to  itself 
other  outlying  matter  and  to  increase  its  bulk  through  growth. 

142 


THE   MECHANISM   OF  DEVELOPMENT  143 

4.  This  growth  is  not  of  bulk  merely,  but  it  is  attended  by 
differentiation,   so    that  one   part   is   distinctly  different    from 
another. 

5.  As  growth  proceeds  bits  of  this  bulk  are  thrown  off,  each 
of  which  constitutes  a  new  individual  capable  of  independent 
existence,  —  reproduction. 

6.  The   new  individual   is  substantially,   but   never  exactly, 
like  the  one  from  which  it  arose,  and  here  lie  the  chief  mys- 
teries of  breeding.    In  reproduction  there  are  no  duplicates. 

Nothing  approaches  this  in  the  inorganic  world  save  crystal- 
lization. Crystals  add  matter  to  their  bulk  and  thus  may  be 
said  to  grow.  Moreover,  the  matter  is  added  in  an  orderly 
manner,  resulting  in  a  kind  of  definite  structure  with  exact 
angles  always  the  same,  but  nothing  like  differentiation  exists. 
One  part  of  the  crystal  is  like  another ;  it  has  no  power  of 
reproduction  and  is  possessed  of  no  force  comparable  with  life. 

The  student  should  early  learn  that  the  field  of  biology  is 
distinct,  but  he  should  also  fully  realize  that  it  lies  within  and 
not  outside  the  range  of  chemistry,  and  that  living  matter  is  not 
freed  from  its  ordinary  affinities  by  reason  of  its  association  with 
life,  but  on  the  contrary  it  continues  as  before  to  be  subject  to 
the  ordinary  physical  and  chemical  relations  of  matter  generally. 
If  he  can  do  this,  he  will  simplify  many  of  his  difficulties. 

SECTION  II— THE  CELL  THE  UNIT  OF  STRUCTURE 

If  a  bit  of  liver,  bone,  wood,  or  any  other  form  of  plant  or 
animal  tissue  be  examined  under  the  microscope,  it  will  be  found 
to  possess  a  definite  structure,  and  to  consist  of  a  large  number 
of  separate  divisions,  each  filled  with  a  gelatinous  mass  called 
protoplasm.  These  separate  divisions  or  cells  are  apparently 
alike  throughout  the  substance  of  any  particular  tissue,  —  as 
the  liver,  —  but  they  differ  greatly  in  different  tissues  of  the 
same  body  (bone,  muscle,  brain).  Biologists  have  been  unwilling 
to  consider  the  individual  as  the  unit,  because  he  is  too  large 
and  his  structure  and  activities  are  too  complicated.  They  have, 
therefore,  chosen  to  regard  the  individual  as  a  colony  of  many 
and  variously  differentiated  cells. 


144  CAUSES  OF  VARIATION 

In  assuming  the  cell  as  a  unit  many  structural  difficulties 
were  solved  to  the  entire  satisfaction  of  the  anatomist,  but  the 
physiological  and  evolutionary  problems  were  complicated  rather 
than  simplified,  because  this  entire  colony  of  many  different  cells 
and  activities  —  heart,  lungs,  liver,  muscles,  nerves,  etc.,  with 
their  many  and  diverse  functions  —  sprang  originally  from  a 
single  cell ;  moreover,  this  colony  will  throw  off  a  succession  of 
single  cells,  each  of  which  will  undergo  specific  and  orderly 
development  and  finally  produce  a  colony  like  the  parent.  This 
being  true,  the  cell  cannot  be  regarded  as  the  ultimate  unit  of 
living  matter,  unless  we  assume  some  kind  of  unity  between  all 
the  cells ;  some  kind  of  intercellular  force  to  insure  that  differ- 
entiation shall  take  place  at  the  proper  points  and  stages,  — 
otherwise  the  original  cell  would  develop  into  a  lump  of  proto- 
plasm or  into  a  colony  of  cells  all  alike. 

The  single  cell  from  which  a  new  individual  is  to  develop 
(the  "  germ  cell"  or  mother  cell)  is  gifted  with  potentialities 
for  the  entire  being,  with  all  its  complications  of  structure  and 
with  all  its  variety  of  function.  Biologists  at  one  time  were 
inclined  to  regard  this  germ  cell  as  "  totipotent,"  that  is,  able 
to  develop  into  almost  any  kind  of  structure  depending  upon 
the  surroundings.  This  view  could  not  hold  because  different 
germ  cells  under  identical  conditions  of  life  develop  each  into 
its  own  species. 

The  cause  of  differentiation,  therefore,  lies  primarily  within, 
and  the  germ  cell  is  to  be  regarded  as  gifted  with  unlimited 
powers  of  development  only  within  the  characters  that  belong  to 
the  species. 

Specific  protoplasm  is,  therefore,  possessed  of  specific  proper- 
ties as  truly  as  is  any  chemical  substance,  and  all  the  characters 
of  structure  or  function  belonging  to  the  mature  individual 
are  to  be  regarded  as  in  some  way  "  inherent  in  the  germ." 
The  cell  is,  therefore,  like  the  individual,  too  large  and  too 
complicated  to  be  considered  as  the  ultimate  unit  'of  living 
matter. 

This  view  is  upheld  not  only  upon  theoretical  grounds  but 
also  by  the  known  facts  of  its  complicated  structure  and  its  re- 
markable behavior  during  cell  division  and  growth, — a  subject 


THE  MECHANISM  OF   DEVELOPMENT 

which  it  were  well  to  consider  before  proceeding  further  with 
the  search  after  the  "  ultimate  unit  of  living  matter,"  and 
therefore  of  growth,  of  differentiation,  and  of  variability. 

SECTION  III— THE  MECHANISM  OF  CELL  DIVISION 
(MITOSIS) 

Growth  in  the  sense  of  increase  of  size  is  the  direct  result  of 
cell  division.  Large  bodies  do  not  have  larger  cells  than  small 
ones,  but  they  have  more  of  them.  Growth  is,  therefore,  in 
proportion  to  cell  division,  — the  mechanism  of  which  is  exceed- 
ingly suggestive  of  the  methods  by  which  lines  of  descent  are 
preserved  and  the  proper  development  assured. 

When  the  protoplasm  of  an  ordinary  growing  cell,  plant  or 
animal,  has  absorbed  material  until  it  has  reached  a  certain  maxi- 
mum size,  it  then  prepares  for  division.  This  is  not  a  lump 
division  in  which  the  new  cells  each  get  one  half  of  the  bulk  of 
the  parent  cell,  but  it  is  qualitative  as  well  as  quantitative,  and 
is  based  on  an  exceedingly  orderly  procedure,  which  insures  not 
only  that  each  daughter  cell  shall  receive  its  share  of  the  mass 
but  also  that  this  share  shall  be  identical  in  quality  with  that 
inherited  by  the  sister  cell  of  the  same  division. 

Those  portions  of  the  cell  contents  most  intimately  concerned 
in  the  process  of  division,  and  therefore  of  chief  interest  here, 
may  be  briefly  described  as  follows  : 

Floating  in  the  general  protoplasmic  mass  (the  cytoplasm)  is 
a  small  body  (the  nucleus)  of  greater  density  than  its  surround- 
ing matter  and  the  evident  seat  and  initial  point  of  all  construc- 
tive processes. 

Scattered  through  the  mass  of  the  nucleus  and  generally,  but 
not  always,  in  the  form  of  minute  granules  is  the  so-called 
"  chromatin  matter,"  named  from  its  intense  reaction  to  staining 
agents. 

These  granules  of  which  the  chromatin  matter  is  (apparently)1 
composed  are  the  "  chromatin  granules  "  of  some  authors,  the 

1  The  word  "  apparently  "  is  inserted  because  the  granular  character  of  chro- 
matin matter  has  not  in  every  case  been  made  out,  and  because  its  granular 
character  is  less  pronounced  at  some  times  than  at  others. 


146  CAUSES  OF  VARIATION 

"  chromomeres  "  of  others,  the  "  microsomes  "  of  still  others, 
and  the  "  ids  "  of  Weismann. 

Lying  generally  in  the  cytoplasm  just  outside  the  nucleus  will 
commonly,  but  not  always,  be  found  an  extremely  minute  highly 
staining  body,  the  centrosome,  about  which,  when  division  is 
about  to  occur,  the  near-by  matter  is  thrown  into  radiating  lines 
like  iron  filings  about  the  poles  of  a  magnet,  giving  the  whole  a 
kind  of  starlike  appearance. 

These  are  the  portions  of  the  cell  most  concerned  in  cell 
divisions,  and  their  special  characters  are  most  pronounced  and 
the  differences  most  distinct  just  previous  to  the  act  of  division, 
and  least  well  marked  in  the  cell  during  its  "  resting  stage  " 
between  divisions. 

The  actual  process  of  cell  division  whereby  one  cell  gives 
rise  to  two  and  by  which  growth  is  attained  is  essentially  as 
follows  : 

When  division  is  about  to  take  place  the  chromatin  matter 
(granules)  assumes  the  appearance  of  a  fine  network  running 
through  the  mass  of  the  nucleus,  the  granules  looking  like  beads 
strung  upon  a  thread.  This  network  commonly,  though  not 
always,  condenses  into  a  ribbon  or  thread  (the  spireme),  which, 
however,  speedily  breaks  up  transversely  into  a  definite  num- 
ber of  segments,  generally  in  the  form  of  short  rods,  straight  or 
curved  (the  chromosomes).  Whether  or  not  the  reticular  or  net- 
work form  passes  through  the  spireme  stage,  the  result  is  always 
the  same ;  namely,  the  chromatin  matter  becomes  divided  into 
a  definite  number  of  chromosomes.  Here  are  two  remarkable 
and  significant  facts  ;  first,  the  number  of  chromosomes  is  con- 
stant in  all  individuals  of  the  same  species  ;  and  second,  "  in  all 
species  arising  by  sexual  reproduction  the  number  is  even!'  1 

While  the  chromatin  matter  has  been  engaged  in  breaking  up 
(or  down)  to  form  the  chromosomes,  another  significant  process 

1  Wilson,  The  Cell,  p.  67.  The  author  here  gives  the  number  of  chromosomes 
characteristic  of  certain  species  as  follows:  some  of  the  sharks,  36;  mouse, 
salamander,  trout,  and  lily,  24;  ox,  guinea  pig,  and  onion,  16;  grasshopper,  12; 
Ascaris,  4  or  2  ;  the  crustacean  Artemia,  168;  man,  16  or  possibly  32.  In  this 
connection  it  is  worthy  of  note  that  varieties  of  the  same  species  often  differ  in 
the  number  of  their  chromosomes,  the  significance  of  which  variation  has  not 
yet  been  determined. 


THE   MECHANISM   OF   DEVELOPMENT 


H7 


has  been  going  on.  The  centrosome  has  divided  and  the  two 
new  bodies  derived  from  it  have  separated  and  migrated  to 
opposite  sides  of  the  nucleus,  each  surrounded  by  its  radiating 
lines,  in  which  condition  they  are  known  as  "asters"  (stars). 

During  this  migration  the  asters  are  generally  (not  always) 
visibly  connected  by  lines,  but  in  either  case  by  the  time  they 
have  reached  opposite  sides  of  the  nucleus  they  will  be  seen  to 
lie  at  opposite  ends  of  a  spindle-shaped  body  (the  amphiaster) 
consisting  of  lines,  among  which  lie  the  chromosomes. 

Matters  are  now  ready  for  the  final  and  significant  acts  of 
cell  division.  The  chromosomes  arrange  themselves  end  to  end 
along  the  equator  of  the  spindle,  and  at  right  angles  to  its  axis  ; 
whereupon  each  chromosome  splits  lengthwise,  one  group  of 
halves  migrating  to  one  aster  (centrosome),  the  other  to  the 
other,  where  each  clusters  about  its  own  center,  forming  a  new 
nucleus  with  its  centrosome.  The  cell  wall  now  becomes  con- 
stricted, dividing  the  cytoplasm  approximately  equally  (some- 
times very  unequally)  between  the  two  new  cells,  and  the  division 
is  complete.  The  resting  stage  ensues,  during  which  preparation 
is  made  for  another  division  ;  indeed,  the  centrosome  occasionally 
divides,  in  anticipation  of  the  next  division,  even  before  all  the 
details  of  the  first  division  are  complete.  For  a  graphic  outline 
of  the  complete  process  of  mitosis  see  Figs.  20  and  21. 

This,  in  general,  is  the  process  of  cell  division  which,  with 
more  or  less  variation,  attends  all  growth.  The  significant  facts 
brought  to  light  in  this  complicated  process  are:  (i)  that  the 
number  of  chromosomes  is  constant  for  all  individuals  within 
the  species  ;  (2)  that  for  all  forms  arising  by  sexual  reproduc- 
tion the  number  is  even ;  (3)  that  however  its  details  may  vary, 
cell  division  consists  essentially  in  a  splitting  of  the  chromo- 
somes, by  which  each  daughter  cell  secures  (apparently)  an 
exact  equivalent  of  what  is  received  by  the  other  daughter  cell 
of  the  same  division.  Cell  division  is  therefore  not  a  lump 
division  of  the  cell  mass,  but  it  is  meristic,  insuring  a  strictly 
qualitative  division  in  which  one  half  of  each  chromosome 
descends  to  either  daughter  cell.1 

1  These  same  facts  have  added  significance  when  considered  in  connection 
with  the  germ  cells,  reproduction,  and  the  problems  of  heredity. 


CAUSES  OF  VARIATION 


Fig.  20.    Diagrams  showing  the  prophases 
of  mitosis 

,  resting  cell  with  reticular  nucleus  and  true  nucleolus  :  at  c  the  attraction  sphere  containing 
two  centromoses.  B,  early  prophase :  the  chromatin  forming  a  continuous  spireme, 
nucleolus  still  present;  above,  the  amphiaster  (a).  C,  D,  two  different  types  of  later 
prophases :  C,  disappearance  of  the  primary  spindle,  divergence  of  the  centrosomes  to 
opposite  poles  of  the  nucleus  (examples,  some  plant  cells,  cleavage  stages  of  many  eggs)  ; 
D,  persistence  of  the  primary  spindle  (to  form  in  some  cases  the  "central  spindle"), 
fading  of  the  nuclear  membrane,  ingrowth  of  the  astral  rays,  segmentation  of  the  spireme 
thread  to  form  the  chromosomes  (examples,  epidermal  cells  of  salamander,  formation  of 
the  polar  bodies).  £,  later  prophase  of  type  C:  fading  of  the  nuclear  membrane  at  the 
poles,  formation  of  a  new  spindle  inside  the  nucleus  ;  precocious  splitting  of  the  chromo- 
somes (the  latter  not  characteristic  of  this  type  alone).  F,  the  mitotic  figure  established ; 
<•/,  the  equatorial  plate  of  chromosomes.  —  After  Wilson 


THE   MECHANISM   OF   DEVELOPMENT 


149 


SECTION  IV— CELL  DIVISION  WITH  AND  WITHOUT 
DIFFERENTIATION 

The  accomplishment  of  this  minutely  accurate  division  of  cer- 
tain portions  of  the  mother  cell  between  the  daughter  cells  at 
division  suggests  two  points  :  (i)  that  the  matter  thus  carefully 


O 


II 


I  J 

Fig.  21.    Diagrams  of  the  later  phases  of  mitosis 

G,  metaphase :  splitting  of  the  chromosomes  (<?/) ;  n,  the  cast-off  nucleolus.  //,  anaphase : 
the  daughter  chromosomes  diverging,  and  between  them  the  interzonal  fibers  (if),  or 
central  spindle ;  centrosomes  already  doubled  in  anticipation  of  the  ensuing  division. 
7,  late  anaphase  or  telophase,  showing  division  of  the  cell  body,  midbody  at  the  equator 
of  the  spindle,  and  beginning  of  reconstruction  of  the  daughter  nuclei.  /,  division  com- 
pleted.—  After  Wilson 

divided  is  of  special  importance  in  shaping  the  activities  of  future 
cells  ;  (2)  that  "daughter  cells  so  provided  should  be  identical, 
and  their  after  growth  should  not  only  be  alike  but  should 


150 


CAUSES  OF  VARIATION 


also  be  similar  to  that  of  the  mother  cell  from  which  they  are 
descended. 

For  all  cell  division  within  the  same  tissue  this  latter  is  true  ; 
that  is  to  say,  in  the  growth  of  liver  tissue,  bone  tissue,  or  any 
other  specific  structure  the  cells  appear  to  be  identical  and 
their  resulting  growths  alike.  But  it  must  not  be  forgotten  that 
these  different  tissues  all  arose  originally  from  a  single  cell ;  in 
other  words,  that  some  cell  divisions  are  attended  by  differenti- 
ation. When  ?  How  ?  Here  lies  the  chief  mystery  of  variation. 
The  mechanism  of  cell  division  would  seem  to  be  specially 
designed  to  prevent  deviation  and  to  insure  absolute  transmission 


Fig.  22.    Pathological  mitosis  in  epidermal  cells  of  salamander  caused  by  poisons 

A,  asymmetrical  mitosis  after  treatment  with  0.05%  antipyrin  solution ;  B,  tripolar  mitosis 
after  treatment  with  0.5%  potassic  iodid  solution.  —  After  Wilson,  from  Galeotti 

from  mother  cell  to  daughter  cell.  It  does  not  account  for  or 
indeed  appear  to  admit  of  differentiation  of  tissues  or  variation 
in  growth.  But  differentiation  does  take  place  and  variation  is 
a  fact  to  be  in  some  way  explained. 

Irregularities  in  cell  division.  Not  all  cell  division,  it  is  true, 
proceeds  with  the  regularity  and  perfection  of  plan  indicated  in 
the  description,  which  is  the  common  method  in  higher  animals 
and  plants  and  may  therefore  be  regarded  as  fairly  typical.  The 
known  abnormal  cases  are  of  several  distinct  kinds  : 

I.  Asymmetrical  mitosis,  in  which  the 'chromosomes  are  not 
equally  distributed  to  the  daughter  cells,  most  of  them  massing 


THE  MECHANISM  OF  DEVELOPMENT  151 

at  one  pole,  some  of  them  perhaps  being  lost  altogether  in  the 
mass  of  the  cytoplasm. 

2.  Multipolar  mitosis,  in  which  the  number  of  centrosomes  is 
more  than  two  and  the  resulting  daughter  cells  three  or  more. 

Both  these  abnormal  processes,  however,  are  characteristic  of 
abnormal  growths,  such  as  cancers  and  tumors,  and  are  therefore 
considered  as  pathological.  It  is  a  suggestive  fact  that  such 
irregularities  may  be  artificially  produced  by  poisons  and  other 


D  E  F 

Fig.  23.    Pathological  mitoses  in  human  cancer  cells 

A,  asymmetrical  mitosis  with  unequal  centrosomes ;  B,  later  stage,  showing  unequal  distri- 
bution of  the  chromosomes ;  C,  quadri polar  mitosis ;  Z>,  tri polar  mitosis';  £,  later  stage  ; 
f,  trinucleate  cell  resulting.  —  After  Wilson,  from  Galeotti 

chemical  substances  such  as  chloral,  quinin,  nicotin,  antipyrin, 
cocain,  etc.1    (See  Figs.  22  and  23.) 

3.  Amitotic  division?  —  that  is,  division  without  the  forma- 
tion of  the  amphiaster  or  the  splitting  of  the  chromosomes. 
This  form  of  cell  division  is  effected  by  constriction,  resulting 
simply  in  a  lump  division  of  the  mass  of  the  nucleus,  without 
reference  to  qualitative  considerations.  In  this  case  the  daughter 
cells  would  not,  presumably,  be  alike.  This  form  of  cell  division 

1  Wilson,  The  Cell,  pp.  97,  98.  Ibid.  p.  114. 


152 


CAUSES  OF  VARIATION 


is  of  rare  occurrence,  is  never  known  in  embryonic  tissues,  and 
is  characteristic  of  tissues  "on  the  way  towards  degeneration."  1 

4.  Quite  generally  unicellular  organisms  display  extreme 
irregularities  in  mitosis,  some  species  omitting  one  and  others 
another  of  the  processes  typical  in  higher  species.  Prominent 
among  these  deviations  is  the  failure  of  chromatin  granules  to 
unite  to  form  definite  chromosomes.  In  place  of  this  the  indi- 
vidual granules  themselves  divide,  suggesting  that  fission  of 
the  granules  is  the  elementary  and  essential  feature  of  nuclear 
division?" 

Other  minor  deviations  are  known,  though  much  of  the 
field  is  yet  unworked.  These  may  account  to  some  extent  for 
differentiation  during  cell  multiplication,  and  yet  so  far  as  is  at 
present  known  all  processes  that  do  not  accomplish  an  equitable 
division  of  the  chromatin  granules  through  the  splitting  process 
are  looked  upon  as  distinctly  pathological.  Normal  cell  division, 
therefore,  seems  to  be  in  the  interest  of  constancy,  not  differentia- 
tion, and  what  power  it  is  that  produces  one  sort  of  tissue  from 
another,  as  must  happen  in  the  developing  embryo,  is  still  a 
mystery. 

SECTION  V  — PHYSIOLOGICAL  UNITS 

This  difficulty  has  led  to  the  assumption  of  some  sort  of  phys- 
iological units,  some  of  which  are  active  at  certain  stages  of 
development,  others  at  other  stages  ;  and  the  chromatin  granules 
whose  qualitative  division  is  in  most  cases  carefully  insured 
are  quite  generally  regarded  as  the  repository  of  these  units 
and  the  common  vehicle  of  hereditary  transmission.  Such  were 
the  gemmules  of  Darwin,3  the  stirp  of  Galton,  the  idioplasm  of 
Nageli,  and  the  determinants  of  Weismann.4 

1  Wilson,  The  Cell,  pp.  116-121.  2  ibid.  p.  90. 

8  See  Darwin,  Animals  and  Plants,  chap,  xxvii. 

4  Weismann's  elaborate  theory  of  heredity  regarded  the  germ  plasm  as  the 
original  substance,  of  which  the  body  is  the  natural  expansion.  This  "ancestral 
germ  plasm  "  is  unchanging,  unchangeable,  and,  so  long  as  the  species  endures,  is 
immortal.  He  regards  this  germ  plasm  as  comprised  ultimately  of  "biophors" 
(life  bearers),  which  may  be  spoken  of  as  living  molecules.  These  biophors,  or 
ultimate  units,  are  combined  in  an  orderly  manner  into  "  determinants,"  whose 
activity  at  development  determines  what  the  particular  part  shall  be.  These 


THE  MECHANISM   OF   DEVELOPMENT  153 

Whether  or  not  any  of  these  theories  finally  hold,  this  signifi- 
cant point  remains,  —  that  an  adequate  theory  of  heredity  must 
account  for  the  following  facts  : 

1.  A  single  cell  thrown  off  from  the  sexual  parts  of  a  mature 
individual   will,   under  proper   conditions,   produce   an  entirely 
new  individual  in  all  essential  respects  like  the  parent,  but  in 
minor  respects  different. 

2.  Commonly  a  cell  or  a  number  of  cells  taken  from  any 
other  part  of  the  body  will  wither  and  die,  or,  if  growth  follows, 
only  one  kind  of  tissue  develops ;  but  in  some  instances  (the 
begonia  and  others)  the  smallest  bit  of  leaf,   under  favorable 
conditions,  is  able  to  grow  and  produce  a  new  plant  capable  of 
bearing  blossoms  and  seeds.1 

3.  The  mechanism  of  cell  division  seems  admirably  adapted 
to  insuring  growth  without  differentiation. 

4.  But    differentiation  does   take    place,   and   in  process   of 
development  a  great  variety  of  different  cells  arise  from  the 
single  original  germ  cell. 

5.  These    "  differentiations "    take    place    at    different    but 
proper  stages,  insuring  orderly  arrangement  and,  for  the  most 
part,  uniform  results. 

6.  There  is  always  more  or  less  variation  between  individuals, 
showing  that  the  problem  of  development  and  inheritance  is 
something  else  than  absolute  descent  without  change. 

We  still  seek,  therefore,  physical  units  with  sufficiently  exact 
properties  to  insure  the  general  character  of  development,  with 
such  mutual  relations  as  shall  provide  for  orderly,  not  simultan- 
eous development,  sufficiently  elastic  in  their  constitution  (or 
combining  powers)  to  admit  of  certain  deviation,  and  each  withal 
gifted  with  the  power  of  nutrition,  growth,  and  multiplication  by 
division.  Such  in  general  are  the  properties  of  the  physiological 

determinants  are  united  into  "  ids,"  which  are  held  to  be  identical  with  chromatin 
granules,  and  these  in  turn  are  assembled  into  "idants,"  which  correspond  with 
chromosomes.  For  a  full  explanation  of  Weismann's  theory,  see  his  Essays  on 
Heredity,  chap,  iv,  and  his  Germ  Plasm,  chap.  i. 

1  It  is  a  significant  fact  that  if  two  begonia  leaves  be  placed  on  sand  simultane- 
ously, one  taken  from  a  plant  just  about  to  blossom,  the  other  from  one  just  past 
the  blossoming  period,  the  plant  from  the  former  will  flower  first.  For  Weismann's 
views,  see  his  Essays  on  Heredity,  chap.  iv. 


154  CAUSES  OF  VARIATION 

units  required  to  explain  the  function  and  achievements  of  the 
germ  plasm,  —  the  bit  of  vitalized  matter  that  holds  within  its 
substance  all  the  potentialities  of  its  particular  kind  of  life. 

Summary.  The  causes  of  variation  are  closely  connected 
with  the  mechanism  of  growth  and  differentiation.  The  cell  is 
the  unit  of  structure  and  all  growth  is  by  cell  division ;  but  it 
is  not  the  unit  of  differentiation  of  different  parts  of  the  body, 
because  all  parts  arise  from  one  original  cell,  the  germ  cell. 

Cell  division  seems  admirably  adapted  to  insure  absolute  trans- 
mission without  variability  of  any  kind.  But  both  differentiation 
and  variability  are  facts.  We  seek,  therefore,  a  "  physiological 
unit"  more  minute  than  the  cell,  whose  activities  and  possibly 
whose  combinations  with  other  physiological  units  of  different 
properties  are  able  to  bring  forth  first  differentiation  within  the 
body  and  later  differences  between  different  individuals. 

ADDITIONAL  REFERENCES 

CHROMOSOME  VESICLES  IN  MATURATION.  By  W.  M.  Smallwood.  Science, 

XXI,  386. 
CYTOLOGICAL    FEATURES   OF    FERTILIZATION.    By    W.    H.    Blackman. 

Proceedings  of  the  Royal  Society,  London,   LXIII,  400-401. 
FERTILITY  OF    EGGS    AFTER    REMOVAL   OF   COCK.     By   L.    G.    Jarvis. 

Experiment  Station  Record,  XI,  671. 
LAWS  OF   EMBRYONIC  DEVELOPMENT:   THE  LAW  OF  VON  BAER.    By 

Otto  Glaser.    Science,  XV,  976-982. 
MECHANISM   OF    DEVELOPMENT.    By    William   Turner,   F.R.S.   Popular 

Science  Monthly,  LVII,  561-575. 
ONTOGENETIC    AND    PHYLOGENETIC    VARIATION.      By    H.    F.    Osborn. 

Science,  IV,  786-789. 

PROBLEM  OF  DEVELOPMENT.  By  E.  B.  Wilson.  Science,  XXI,  281-293. 
PROTOPLASMIC  STRUCTURE.  By  E.  B.  Wilson.  Science,  II,  893-899; 

X,  33-45- 

SOME  OBSERVATIONS  AND  CONSIDERATIONS  UPON  MATURATION  PHE- 
NOMENA   OF    GERM    CELLS.     By   T.    H.    Montgomery.     Biological 

Bulletin,  VI,  1904. 
STRUCTURE    AND    FORMATION    OF    Pus    CELLS.     Experiment    Station 

Record,  XIV,  1016. 
VITALITY  OF  POLLEN.     (Roses,  twenty-two  days;  clivias,  three  months.) 

Experiment  Station  Record,  XIII,  620;   (Bear,  thirty  days)  XV,  872. 


CHAPTER   VIII 

INTERNAL  CAUSES  OF  VARIATION 

While  the  causes  of  variation  are  both  internal  and  external 
to  the  organism,  the  facts  of  the  last  chapter  must  satisfy 
the  student  of  breeding  problems  that  many  of  the  processes 
attendant  upon  growth  and  reproduction  are  fruitful  sources  of 
variability.  It  is  the  purpose  of  the  present  chapter  to  discuss 
these  internal  influences  somewhat  at  length.  They  are  of  two 
kinds,  —  (i)  those  affecting  the  individual  only,  and  (2)  those 
affecting  the  race  as  a  whole.  It  is  expedient  to  distinguish 
between  these  two  classes,  and  the  chapter  will  be  divided  into 
two  parts,  corresponding  to  these  distinctions,  as  follows:  (i) 
internal  influences  affecting  primarily  the  individual ;  (2)  internal 
influences  affecting  the  race  as  a  whole. 

I— INTERNAL  INFLUENCES  AFFECTING  PRIMARILY 
THE  INDIVIDUAL 

SECTION   I— CELL  DIVISION 

Growth  is  the  result  of  cell  division.  Manifestly,  therefore, 
all  differences  in  size  or  in  pattern  are  intimately  dependent  upon 
the  extent  and  regularity  of  this  process. 

Morphological  variation  due  to  cell  division.  Whatever  influ- 
ences underlie  the  phenomena  of  mitosis,  all  questions  of  form 
or  size  are  absolutely  dependent  upon  the  extent  to  which  cell 
division  and  its  attendant  growth  proceed.  The  individual  cells 
in  giants  are  not  larger  than  those  of  normal  specimens,  but  they 
are  more  numerous  ;  and  in  dwarfs  they  are  not  smaller,  but 
fewer  in  number.1  What  energies  decide  how  far  cell  division 
shall  proceed  and  when  it  shall  stop  in  the  case  of  each  separate 

i  Wilson,  The  Cell,  pp.  388-389. 
'55 


156  CAUSES  OF  VARIATION 

organ  we  do  not  know.  Food  and  climate  undoubtedly  exert  a 
general  influence,  as  we  shall  see,  but  altogether  aside  from  this 
there  must  be  profound  internal  forces  or  interrelationships, 
upon  the  normal  exercise  of  which  all  typical  results  depend. 

Consider  the  development  of  a  normal  individual  from  the 
fertilized  ovum  to  maturity.  The  circumstances  require  not  only 
that  arm,  leg,  and  bone,  heart,  liver,  and  brain,  arise  at  the  proper 
time  and  place,  but  also  that  the  attendant  cell  divisions  in  each 
proceed  to  the  requisite  number  and  then  stop.  If  the  number  be 
too  few,  a  dwarf  is  the  result;  if  too  large,  a  giant ;  and  if  too 
few  in  some  parts  (arrested  development)  or  too  large  in  others 
(hypertrophy),  the  individual  is  thrown  out  of  proportion  and  is 
recognized  as  more  or  less  of  a  monstrosity  according  to  the 
degree  of  disproportion.  To  be  sure,  all  these  things  occasion- 
ally happen,  and  yet,  in  the  majority  of  cases,  the  process  of 
cell  division  is  adjusted  with  a  nicety  that  is  nothing  short  of 
marvelous ;  in  any  event,  the  results  secured,  though  varying 
somewhat  in  total  development,  are  yet  almost  absolutely 
proportional  (P).1 

Whatever  may  be  the  controlling  force  to  decide  at  what  point 
cell  division  in  each  case  shall  stop  and  when  the  individual  as 
a  whole  shall  cease  to  grow,  the  plain  physiological  fact  is  that 
all  considerations  of  size  (quantitative  variation)  are  fundamen- 
tally those  of  cell  division. 

The  cessation  of  growth  at  maturity  does  not  imply  the  loss 
of  power  of  cell  division,  because  most  forms  of  life,  plant  or  ani- 
mal, have  more  or  less  powers  of  regeneration  if  a  part  is  lost 
or  injured.  If  a  leg  of  a  salamander  be  cut  away,  it  will  speedily 
be  restored,  bones  and  all,  as  good  as  new.  A  tail  of  a  lizard  is 
readily  broken  off,  separating  not  between  two  vertebrae  but  at 
the  middle  of  a  vertebra  (in  some  species  generally  the  seventh 
caudal).2  When  the  tail  regenerates,  however,  the  vertebrae  do 

1  At  this  point  the  author  questions  his  own  statement.  As  a  matter  of  fact, 
the  data  involved  have  not  been  submitted  to  absolute  mathematical  determina- 
tion. We  do  not  know  whether  the  normal  deviation  in  size  due  to  variation  in 
cell  division  is  the  same  for  all  species ;  nor  do  we  know  whether  in  giants  and 
dwarfs  all  parts  bear  the  same  relative  proportions  as  in  normal  specimens ; 
indeed,  there  is  ground  for  believing  that  they  do  not.  In  the  most  general 
sense,  however,  the  statement  is  true.  2  Morgan,  Regeneration,  p.  198. 


INTERNAL  CAUSES  OF  VARIATION  157 

not  regenerate,  and  in  their  place  there  is  only  a  "cartilaginous 
tube  attached  to  the  broken  vertebra."  1 

In  the  first  case  (that  of  the  salamander)  cell  division,  which 
would  normally  remain  suspended  through  life,  was  able  upon 
occasion  not  only  to  resume  activity  but  also  to  begin  back  at  the 
proper  point  in  ontogeny  2  and  repeat  its  normal  processes  from 
that  point  onward.  Moreover,  in  this  particular  instance  it  can 
do  this  not  once  but  many  times.3  In  the  lizard,  on  the  other 
hand,  regeneration  is  not  complete,  as  no  true  vertebrae  are 
formed.  Higher  animals  generally  have  but  slight  powers  of 
regeneration,  but  all  have  enough  to  repair  ordinary  injuries  to 
the  skin,  bone,  nerves,  etc.,  showing  that  the  power  of  cell 
division  is  not  entirely  lost  at  maturity;  in  other  words,  that 
cessation  of  growth  when  the  normal  size  is  reached  is  due  to 
some  cause  other  than  the  failure  of  the  power  of  cell  division. 
There  are  many  cases  of  abnormal  size  of  certain  parts  due  to  a 
failure  of  this  process  to  arrest  itself  at  or  near  the  proper 
point.  "Big  heads,"  "giant  kidneys,"  and  similar  pathological 
cases  are  instances  in  point,  but  whether  the  division  is  mitotic 
or  amitotic  has  not,  so  far  as  the  writer  is  informed,  been 
determined. 

While  the  limitation  of  cell  division  can  certainly  be  influenced, 
especially  by  the  food  supply  and  by  exercise,  it  is  manifest  that 
its  absolute  control  is,  and  doubtless  always  will  be,  largely  beyond 
our  power.  All  animals  get  feed  enough  to  more  than  build  their 
bodies,  and  the  point  at  which  growth  ceases  seems  to  be  mainly 
constitutional.  If  we  could  regulate  size  directly,  it  would  vastly 
simplify  the  process  of  breeding,  but  as  it  is  now,  we  are  obliged 
to  "  breed  for  size  "  and  feed  accordingly. 

1  Morgan,  Regeneration,  p.  198. 

2  Ontogeny  refers  to  the  development  of  the  individual,  as  phylogeny  refers  to 
that  of  the  race. 

3  The  absolute  limits  of  regeneration  are  not  known.    Speaking  generally,  they 
are  high  in  plants  and  low  in  animals.    The  salamander  has  been  known,  however, 
to  restore  tail  and  all  four  legs  six  successive  times  (Morgan,  Regeneration,  p.  5). 
The  deer  grows  a  new  set  of  antlers  every  year.    This  is  hardly  a  case  of  regener- 
ation, however,  because  successive  growths  are  each  more  complicated  than  the 
former,  each  adding  its  characteristic  prong;  but  it  is  a  good  instance  to  show  the 
persistence  of  the  power  of  cell  division. 


158  CAUSES  OF  VARIATION 

• 

Meristic  variation  in  general  due  to  cell  division.  All  differen- 
tiation involving  numbers  of  duplicate  parts  manifestly  has  its 
seat  in  cell  division.  An  additional  division  at  the  point  of  origin 
of  the  series  doubles  the  number,  but  an  extra  division  at  the 
point  of  origin  of  a  member  adds  a  pair,  if  both  daughter  cells 
develop,  or  a  single  member  if  but  one  develops. 

When  the  number  in  a  meristic  series  is  even  the  series  is 
easily  conceivable  as  having  arisen  from  a  corresponding  number 
of  cell  divisions.  For  example  : 

2  in  the  series,  i  division 

4  in  the  series,  2  divisions 

6  in  the  series,  2  divisions,  with  one  pair  dividing  again 

8  in  the  series,  3  divisions 

10  in  the  series,  3  divisions,  with  one  pair  dividing  again 

If  the  number  of  members  is  odd,  it  is  only  necessary  to  assume 
that  one  of  the  even  numbers  failed  to  develop,  or,  what  is  more 
likely,  that  one  of  a  pair  indulges  in  additional  division,  —  its 
sister  member  remaining  single  ;  thus  : 

3  members,  i  division,  one  member  dividing  again 

5  members,  2  divisions,  one  member  dividing  again 

7  members,  2  divisions,  three  members  dividing  again 

9  members,  3  divisions,  one  member  dividing  again 

The  frequent  recurrence  of  five  as  a  digital  number  is  one  of 
the  mysteries  in  creation,  and  its  singular  persistence  is  another. 
It  is,  however,  subject  to  many  deviations,  as  was  seen  in  the 
chapter  on  " Meristic  Variation";  even  in  the  rose  family  there 
is  an  occasional  loss  of  one  of  the  members. 

The  frequent  presence  of  six  digits  is  not  to  be  explained  by 
reversion,  as  nobody  supposes  that  number  ever  to  have  been 
characteristic  in  any  species,  —  a  fact  that  should  be  noted  by 
some  of  our  friends  who  are  always  ready  to  invoke  the  aid  of 
atavism  to  explain  every  abnormality. 

Meristic  variation,  like  other  deviations  arising  from  external 
causes,  is  to  some  extent  hereditary,  and  capable  of  being  in- 
fluenced, if  not  absolutely  controlled,  through  selection.  No 
other  method  is  known,  aside  from  the  fact  that  external  injury 


INTERNAL  CAUSES  OF  VARIATION 


'59 


to  many  plants  and  certain  animals  results  in  budding  and  mul- 
tiplication of  parts.  We  cut  the  main  stem  of  a  small  tree  or 
shrub  in  order  to  increase  the  number  of  side  branches.  Some- 
what similarly,  injured  parts  are  often  doubled  in  regeneration.1 
In  this  way  lizards  may  be  made  to  produce  an  increased  number 
of  toes  and  even  double  feet,  legs,  and  tail.  It  is  supposed  that 
double  feet,  sometimes  seen  even  in  mammals,  may  be  produced 
by  a  "  fold  of  the  amnion  constricting  the  middle  of  the  begin- 
ning of  the  young  leg  "  2  in  the  embryo.  This,  however,  is  curi- 
ous rather  than  valuable  to  us,  as  it  tends  to  explain  abnormalities 
rather  than  to  point  a  way  to  practical  improvement. 

Irregularities  in  cell  division  a  cause  of  variation.3  The  char- 
acteristic act  in  cell  division  seems  to  be  the  splitting  of  the 
chromosomes  (or  chromatin  granules)  and  the  migration  of  exact 
equivalents  to  each  new  daughter  cell,  strongly  suggesting  that 
the  assortment  of  "  physiological  units  "  (whatever  they  may  be) 
received  by  one  daughter  cell  is  an  exact  duplicate  of  that  received 
by  the  other,  thus  insuring  an  orderly  and  systematic  develop- 
ment through  a  strictly  qualitative  division  of  hereditary  sub- 
stance at  each  and  every  stage  of  growth. 

The  whole  mechanism  of  mitosis  seems  adjusted  to  this  end, 
and  if  the  assumption  is  true  its  significance  can  hardly  be  over- 
estimated. If  this  careful  adjustment  of  the  mechanism  of  cell 
division  is  necessary  to  orderly  development,  it  is  manifest  that 
any  substantial  deviation  is  likely,  if  not  certain,  to  result  in 
variation  more  or  less  profound.  Such  deviation  is  characteristic 
of  amitotic  division  generally,  and  it  is  more  than  conceivable 
that  the  ordinary  process  is  subject  to  occasional  "  slips."  Some 
chromatin  granule  may  fail  to  divide  at  the  proper  moment  and 
may  pass  over  to  one  daughter  cell  entire,4  or,  conversely,  it 
may  indulge  in  an  extra  division.  Substantial  deviations  in  the 
process  are  known  to  occur  not  rarely  but  frequently.  For  ex- 
ample, the  splitting-  sometimes  takes  place  in  the  spireme  stage, 
sometimes  after  the  formation  of  the  chromosomes  ;  sometimes 

1  Morgan,  Regeneration,  pp.  137-139. 

2  Ibid.  p.  139. 

3  See  previous  chapter. 

4  This  is  known  to  occur  in  certain  instances  in  maturation. 


l6o  CAUSES  OF  VARIATION 

the  centrosome  divides  before  the  resting  stage,  more  commonly 
afterward.  Taking  it  all  in  all,  here  is  an  exceedingly  compli- 
cated procedure,  only  semi-mechanical  and  therefore  subject  to 
deviations.  Absolute  constancy  demands  no  failure  in  the  final 
object  of  exact  qualitative  division,  but  the  student  sees  many 
possibilities  for  unequal  division  and  therefore  for  deviation  in 
growth.  Is  this  the  fundamental  cause  of  mutations  ?  One  thing 
is  certain, — living  forms  are  made  up  of  elements,  and  these 
elements  are  subject  to  strange  combinations  throughout  the 
entire  range  of  plant  and  animal  life,  and  the  facts  seem  to  teach 
that  from  time  to  time  combinations  may  arise  that  are  entirely 
new.  Moreover,  whole  units  seem  occasionally  to  be  "  lost  out," 
as  when  horned  cattle  suddenly  give  rise  to  polled  strains,  hairy 
species  to  smooth  varieties,  colored  to  albino,  etc. 

Conversely,  do  vital  elements  like  chemical  radicles  assume 
new  combinations  from  time  to  time,  giving  rise  to  new  char- 
acters and  new  types  which  we  call  "  mutants  "  ?  We  do  not 
know,  and  yet  we  feel  the  conviction  that  at  this  point  we  are 
very  close  to  the  "  origin  of  characters,"  the  cause  of  mutations 
and  of  variation  in  general. 

Manifestly,  in  so  far  as  irregularities  in  cell  division  may  be  a 
cause  of  variation,  the  matter  lies  absolutely  beyond  our  control 
except  that  lines  in  which  it  is  believed  to  occur  may  be  avoided 
in  selection.  Here  is  a  field,  however,  too  far  beyond  our  pres- 
ent knowledge  to  admit  of  anything  more  than  the  merest 
mention.  We  confidently  believe  that  the  future  will  shed  more 
light  on  this  obscure  subject. 


SECTION  II— BISEXUAL  REPRODUCTION  A  FUNDAMENTAL 
CAUSE  OF  VARIATION 

Among  higher  animals  and  plants  the  new  individual  is  the 
direct  product  of  two  others,  —  the  male  and  the  female  parent, 
-and  is  of  necessity  different  from  either,  being  a  product  of 
both.  In  bisexual  reproduction,  therefore,  biologists  recognize  a 
fundamental  cause  of  variation,  —  slight  if  the  parents  are  of  like 
blood  lines,  extreme  if  of  radically  different,  as  in  hybridism. 


INTERNAL  CAUSES  OF   VARIATION  161 

This  view  of  the  case  is  borne  out  by  the  facts  of  fecundation 
or  fertilization  of  the  ovum,  which  may  be  briefly  described  as 
follows  : l 

The  ovum.  This  is  the  finished  product  of  the  sexual  cells  of 
the  mother  parent,  and  consists  of  a  nucleus  with  its  character- 
istic chromatin  granules  surrounded  by  a  comparatively  large 
mass  of  cytoplasm.  Its  equivalent  in  plants  is  the  ovule. 

The  spermatozoon.  This  is  the  characteristic  product  of  the 
sexual  cells  of  the  male  in  animals,  and  is  the  functional  equiva- 
lent of  the  pollen  grain  and  the  spermatozoid  of  plants.  It  is 
in  all  cases  vastly  smaller  than  the  corresponding  ovum,  being 
almost  destitute  of  cytoplasm.  The  characteristic  elements  of 
the  ovum  are  its  nucleus  and  the  cytoplasm,  while  the  character- 
istic elements  of  the  spermatozoon  are  its  nucleus,  borne  in  the 
"head,"  and  a  centrosome,  generally  carried  in  the  " middle 
piece."  The  tail,  formed  from  the  small  amount  of  cytoplasm, 
seems  to  have  no  function  beyond  providing  motile  power,  and  is 
absent  in  the  pollen  of  higher  plants. 

Fertilization.  Both  the  ovum  and  the  sperm  cell  have  arisen 
in  their  respective  organs  by  the  method  of  cell  division,  display- 
ing in  the  process  the  ordinary  phenomena  of  mitosis.2  But 
both  have  reached  the  end  of  their  powers  of  self-division,  and  if 
left  alone  they  will  be  thrown  off  from  their  respective  points  of 
origin  to  wither  and  die. 

If,  however,  they  are  brought  near  together,  mutual  attraction 
ensues,  the  spermatozoon  (or  other  sperm  cell)  enters  the  ovum, 
the  nuclei  approach  each  other  and  fuse,  the  centrosome  divides, 
an  amphiaster  is  formed,  and  cell  division  ensues.  The  ovum  is 
now  fertilized,  segmentation  proceeds,  and  a  new  individual  is 
established  in  an  independent  existence. 

The  new  individual  is  thus  the  possessor  of  actual  living  mat- 
ter (physiological  units)  derived  from  both  parents,  and  thus 
inherits  literally  the  substance  of  both,  having  come  into  direct 
possession  of  material  identical  with  the  living  matter  of  both 
parents. 

1  For  a  fuller  discussion  of  this  subject,  see  Wilson,  The  Cell,  pp.  178-231. 

2  For  a  brief  statement  of  what  is  involved  in  maturation,  see  the  next 
section. 


1 62  CAUSES  OF  VARIATION 

All  that  is  involved  in  fertilization  is  not  well  understood,  but 
its  essential  feature  is  the  union  or  fusion  of  tJic  nuclear  matter 
(mingling  of  the  chromosomes)  from  two  parents  to  form  the 
cleavage  or  segmentation  nucleus  whose  subsequent  growtJi  and 
divisions  "give  rise  to  all  the  nuclei  of  the  body."  This  fertilized 
ovum  becomes,  therefore,  the  first  cell  of  the  new  being,  which 
inherits  directly  and  equally  a  portion  of  the  nuclear  matter  from 
both  parents,  so  that  "  every  nucleus  of  the  child  may  contain 
nuclear  substance  derived  from  both  parents."  *  Here,  then,  is 
the  avenue  of  all  inheritance,  and,  as  the  new  individual  is  a  kind 
of  blend  of  both  parents,  we  see  in  fertilization  an  initial  and 
primary  cause  of  variation. 

This  is  the  only  form  of  variation  recognized  by  Weismann  in 
his  earlier  writings  as  in  any  sense  hereditary.  All  deviations 
in  development  due  to  external  causes  were  conceived  to  affect 
the  body  (soma  plasm2)  only,  exerting  no  influence  upon  the 
ancestral  germ  plasm.3  True,  he  later  announced  the  theory  of 
germinal  selection,  in  which  a  kind  of  struggle  for  existence  is 
conceived  as  taking  place  between  the  "biophors  "  (physiological 
units),  by  which  some  prosper  and  multiply  exceedingly  while 
others  are  crowded  out  entirely.4  This  would  give  another  cause 
of  variation  within  the  germ  plasm  of  each  individual. 

Biologists  generally  recognize  internal  causes  of  variation 
other  than  these,  and  yet  this  union  of  the  chromosomes  from 
different  individuals  taking  place  at  each  new  generation  must  be 
regarded  as  a  very  effective  means  of  introducing  variability. 
Even  if  the  offspring  of  a  single  parent,  as  in  parthenogenesis, 
should  be  an  exact  duplicate  of  the  parent,  —  which  it  is  not,  - 
every  one  would  recognize  the  fact  that  the  blending  of  heredi- 
tary substance  from  two  parents  must  of  necessity  produce  an 
individual  with  a  new  combination  of  faculties. 

It  is  a  variation,  however,  confined  not  only  to  the  characters 
of  the  race  but  also  to  the  family  possessions  of  the  particular 
parents.  Bisexual  reproduction  cannot  be  looked  upon  as  a  means 

1  Wilson,  The  Cell,  p.  182. 

"  Soma  plasm  "  is  a  term  used  to  represent  the  protoplasms  of  the  body  in 
general  as  distinct  from  the  output  of  the  sexual  cells  (germ  plasm). 
8  Weismann,  The  Germ  Plasm,  chap.  ix. 
*  Weismann,  Germinal  Selection  (pamphlet). 


INTERNAL  CAUSES  OF  VARIATION  163 

of  introducing  new  characters  into  the  race,  and  while  it  is  mani- 
festly a  fruitful  source  of  never-ending  combinations  of  racial 
characters  in  new  individuals,  yet  variations  so  introduced  are 
comparatively  slight  except  when  the  two  parents  belong  to  sepa- 
rate lines. 

Fertilization  of  the  ovum  is  something  more  than  a  stimulus 
to  growth.  It  is  a  real  union  of  material  bodies,  physiological 
units,  or  whatever  they  may  be  called,  representing  the  hereditary 
substance  of  both  parents.  Bisexual  reproduction  is  therefore 
not  only  a  guaranty  of  transmission  of  racial  characters  but  also 
an  assurance  of  inheritance  with  some  variation. 

Control.  Here  is  a  fundamental  cause  of  variation  practically 
under  the  control  of  the  breeder  through  selection.  True,  his 
knowledge  and  his  judgment  are  insufficient  to  insure  him  against 
mistakes  in  mating,  and  it  is  also  true  that  there  are  many  other 
influences  at  work  to  produce  variations,  but  this  is  the  field  in 
which  the  breeder  can  exert  the  largest  influence,  and  it  is  by 
selection  that  the  greatest  results  in  improvement  have  been 
attained  up  to  date. 

Sexual  selection,1  preferential  mating,2  and  assortative  mating.3 
Powerful  as  are  these  influences  in  directing  the  trend  of  varia- 
bility, they  yet  belong  to  general  evolution  because  they  are  ele- 
ments in  natural  selection,  and  they  have  no  place  in  the  present 
discussion. 

SECTION    III  —  MATURATION    AND   THE    REDUCTION    OF 
THE   CHROMOSOMES  A  CAUSE  OF  VARIATION 

Fertilization  is  a  process  whose  inevitable  consequence  would 
seem  to  be  the  "piling  up  "  of  nuclear  matter  indefinitely  ;  for 
if,  with  each  new  generation,  the  chromosomes  (or  physiological 
units)  of  the  one  parent  are  added  to  those  of  the  other,  it  would 
seem  that  in  time  the  resulting  nuclear  matter  would  speedily 
become  "  unmanageably  large  "  and  inconceivably  complex,  — an 
event  certain  to  follow  except  for  a  series  of  very  remarkable 

1  Darwin,  Origin  of  Species,  see  Index. 

2  Pearson,  Grammar  of  Science,  pp.  425-428. 

3  Ibid.  pp.  429-437. 


!64  CAUSES  OF  VARIATION 

facts  occurring  just  previous  to  fertilization  and  by  which  the 
number  of  chromosomes  in  both  the  male  and  female  germ  cells  is 
reduced  to  one  half  the  usual  or  somatic  number,  so  that  their 
union  at  fertilization  restores  the  true  number  of  chromosomes 
typical  of  the  race.  Thus,  if  the  somatic  number  of  chromosomes 
is  sixteen,  the  number  in  the  germ  cells  at  fertilization  will  be 
eight  each,  or  sixteen  after  fusion  of  the  nuclei.  This  process  by 
which  the  number  of  chromosomes  is  halved  in  the  germ  cell  is 
known  as  reduction,  and  is  supposed  to  be  the  significant  feature 
of  the  maturation  process  by  which  the  male  and  female  germ 
cells  are  prepared  for  union. 

Parallelism  in  the  sexes.  Maturation  and  its  attendant  phe- 
nomena of  reduction  in  the  number  of  chromosomes  is  a  subject 
that  must  be  considered  separately  in  the  male  and  the  female, 
and  yet  there  exists  a  strange  parallelism  worthy  of  notice.  To 
quote  Wilson  J : 

Recent  research  has  shown  that  maturation  conforms  to  the  same  type 
in  both  sexes.  .  .  .  Stated  in  the  most  general  terms  this  parallel  is  as  fol- 
lows :  In  both  sexes  the  final  reduction  in  the  number  of  chromosomes  is 
effected  in  the  course  of  the  last  two  cell  divisions,  or  maturation  divisions 
[as  they  are  called],  by  which  the  definitive  germ  cells  arise,  each  of  the 
four  cells  thus  formed  having  but  half  the  usual  number  of  chromosomes. 
In  the  female  but  one  of  the  four  cells  [resulting  from  the  two  maturation 
divisions]  forms  the  ovum  proper,  while  the  other  three,  known  as  the 
polar  bodies?  are  minute,  rudimentary,  and  incapable  of  development.  In 
the  male,  on  the  other  hand,  all  four  of  the  cells  become  functional  sper- 
matozoa. This  difference  between  the  two  sexes  is  probably  due  to  the 
physiological  division  of  labor  between  the  germ  cells,  the  spermatozoa 
being  motile  and  very  small,  while  the  egg  contains  a  large  amount  of 
protoplasm  and  yolk,  out  of  which  the  main  mass  of  the  embryonic  body  is 
formed.  In  the  male,  therefore,  all  of  the  four  cells  may  3  become  func- 
tional ;  in  the  female  the  functions  of  development  have  become  restricted 
to  but  one  of  the  four,  while  the  others  have  become  rudimentary. 

1  Wilson,  The  Cell,  p.  234. 

2  The  author  is  here  speaking  specifically   of  reproduction    in   animals,   as 
plants  do  not  form  polar  bodies.    The  difference  in  plant  and  animal  reproduc- 
tion is,  however,  more  in  form  than  in  significance. 

8  The  author  says  "  may  "  become  functional.  He  means  by  this  that  each  of 
the  four  cells  (spermatozoa)  arising  from  the  last  two  divisions  is  capable  of 
fertilizing  an  ovum,  while  of  the  four  cells  arising  from  the  last  two  divisions  in 
the  female  only  one  is  capable  of  being  fertilized. 


INTERNAL  CAUSES  OF  VARIATION  165. 

Maturation  and  reduction  in  animals  and  in  plants  different  in 
appearance  but  not  in  fact.  This  remarkably  significant  process 
is  fundamentally  the  same  in  animals  and  plants,  differing  con- 
siderably, however,  in  detail.  It  is  simpler  in  animals  and  more 
direct.  In  them  the  'last  two  cell  divisions  always  (apparently) 
give  rise  in  the  male  to  four  functional  spermatozoa,  but  in  the 
female  to  one  functional  cell,  retaining  nearly  all  the  cytoplasm, 
and  to  three  polar  bodies  incapable  of  fertilization  and  destined 
to  wither  away  and  disappear.  The  same  general  facts  seem  to 
hold  for  animals  of  all  species,  and  Wilson  remarks  1 : 

The  evidence  is  steadily  accumulating  that  reduction  is  accomplished 
by  two  maturation  divisions  throughout  the  animal  kingdom,  even  in  the 
unicellular  forms  ;  though  in  certain  Infusoria  an  additional  division  occurs, 
while  in  some  other  Protozoa  only  one  maturation  division  has  thus  far 
been  made  out. 

Among  plants,  also,  two  maturation  divisions  occur  in  all  the  higher 
forms,  and  in  some  at  least  of  the  lower  ones.  Here,  however,  the  phe- 
nomena are  complicated  by  the  fact  that  the  two  divisions  do  not,  as  a  rule, 
give  rise  directly  to  the  four  sexual  germ  cells,  but  to  asexual  spores  which 
undergo  additional  divisions  before  the  definitive  germ  cells  are  produced.2 
[The  end  product,  however,  shows  the  same  reduction  in  the  number  of 
chromosomes.] 

A  brief  description  of  reduction  in  animals  is  worth  consider- 
ing somewhat  in  detail,  as  it  is  fairly  well  known  and  cannot 
fail  to  impress  the  student  with  its  fundamental  significance  and 
the  nicety  of  adjustment  of  the  mechanism  of  living  processes. 

Reduction  in  the  female.3  Among  animals  the  production  of 
the  female  germ  cell  (the  ovum)  is  the  special  function  of  the 
ovaries.  In  the  tissues  of  these  organs  cell  division  proceeds 
under  the  usual  mitotic  plan,  giving  rise  to  a  series  of  cells 
known  as  oogonia.  At  a  certain  point  mitotic  division  halts,  and 
each  cell  prepares  for  the  final  (maturation)  changes.  Food 
material  is  absorbed,  the  cytoplasm  increases  in  bulk,  the  nucleus 
greatly  enlarges,  and  the  cell,  now  known  as  an  oocyte,  is  ready 

1  Wilson,  The  Cell,  p.  235. 

2  Ibid.  pp.  235-236.    Note  that,  in  general,  polar  bodies  are  not  formed  in 
plants. 

3  Ibid.  pp.  236-240.    This  description  applies  to  the  animal.  The  details  are 
distinctly  different  in  plants,  to  be  discussed  later. 


1 66  CAUSES  OF  VARIATION 

for  the  last  two,  or  maturation,  divisions.  In  this  condition  the 
egg  cell  remains  until  near  the  time  of  fertilization,  when  the 
process  of  maturation  proper  takes  place. 

The  significant  details  of  this  interesting  series  of  changes  are 
concerned  with  the  nucleus  and  are  substantially  as  follows: 
During  the  long  resting  stage  preparatory  to  these  final  divisions 
the  nucleus  increases  in  bulk  and  the  chromatin  matter  assumes 
the  reticular  form  characteristic  of  the  resting  stage  of  dividing 
cells  in  general.  In  this  condition  the  nucleus  is  known  as  the 
"germinal  vesicle."  Up  to  this  point  the  number  of  chromo- 
somes is  the  same  as  that  of  the  body  cells  in  general.  Their 
identity  is,  of  course,  now  lost,  but  as  the  time  for  the  first 
maturation  division  arrives,  instead  of  the  spireme  of  ordinary 
mitosis  breaking  up  into  the  usual  number  of  chromosomes, 
there  appear  more  or  less  spontaneously  a  number  of  "primary 
chromatin  masses  "  in  the  form  of  rods,  rings,  or  V-shaped  bodies, 
each  of  which  ultimately  breaks  up  into  four  smaller  bodies. 
These  groups  of  four  are  always  one  half  the  usual  or  'somatic 
number  of  chromosomes. 

Whether  the  chromatin  masses  appear  in  the  form  of  rods, 
rings,  or  otherwise,  the  final  result  seems  to  be  always  the  same  ; 
namely,  the  breaking  up  of  each  into  four  smaller  bodies,  either 
by  two  longitudinal  divisions  or  by  one  (the  first)  longitudinal 
and  one  transverse.  The  details  differ  in  different  species  and 
have  been  worked  out  in  but  few  cases.  It  is  not  important 
here  to  trace  the  bewildering  differences,  but  rather  to  describe 
typical  behavior.1 

Having  assumed  this  condition  the  nucleus  now  migrates  to 
the  margin  of  the  cell,  each  of  the  groups  of  four  (tetrads  in  rod- 
shaped  cases)  splitting  into  two  smaller  groups  of  two  each 
(dyads).2  The  mass  now  divides,  one  pair  from  each  group 

1  For  a  full  discussion  of  the  different  forms  of  reduction,  see  Wilson,  The 
Cell,  V,  233-287. 

2  The  terms  "  tetrad "  and  "  dyad  "  of  course  apply  only  in  the  case  of  rod- 
shaped  masses.    In  the  case  of  rings  (common  in  animals)  and  V-shaped  masses 
(common  in  plants)  the  parting  into  four  takes  place  gradually  as  the  work  pro- 
ceeds, while  in  the  case  of  rods  the  division  into  four  takes  place  early  and  the 
parts  are  distinct  from  the  first.    In  this  formation  the  two  divisions  take  place 
much  more  rapidly  than  in  the  case  of  rings,  which  split  and  divide  slowly.    The 


INTERNAL  CAUSES  OF  VARIATION  167 

remaining  in  the  cell,  the  other  passing  outside,  forming  the 
first  polar  body,  which  may  or  may  not  undergo  further  division. 

The  portion  now  remaining  within  the  cell  consists  of  groups 
of  two  each,  instead  of  four,  and  their  number  is  of  course  the 
same  as  before,  namely,  one  half  the  somatic  number  of  chromo- 
somes. Immediately  now,  without  assuming  the  resting  stage, 
the  dyads,  or  groups  of  twos,  turn  one  fourth  around,  taking  a 
position  at  right  angles  to  the  margin  of  the  cell,  and  at  once 
divide  again,  one  member  of  each  pair  remaining  behind  in  the 
egg  cell,  the  other  passing  out,  forming  the  second  polar  body. 

The  first  polar  body  carried  away  one  half  the  nuclear  matter, 
and  the  remaining  half  has  now  been  divided  equally  between 
the  second  polar  body  and  the  main  cell,  which  is  now  ready  for 
fertilization  and  is  from  this  time  on  spoken  of  as  the  ovum. 

Neither  polar  body  carries  any  appreciable  quantity  of  cyto- 
plasm, and  both  are  destined  to  degenerate  and  disappear.  The 
first  one,  however,  containing  half  of  the  total  nuclear  matter, 
commonly  divides  once,  so  that  the  first  polar  body  represents 
not  one,  but  two  cells,  —  the  first  and  the  third  polar  bodies. 

The  total  result,  then,  of  this  complicated  process  seems  to 
be  the  equal  division  of  the  chromatin  matter  between  the 
ovum,  capable  of  fertilization,  and  three  polar  bodies,  destined 
to  extinction. 

A  group  of  four  cells  thus  arises,  — -  namely,  the  mature  egg 
(ovum),  which  after  fertilization  gives  rise  to  the  embryo,  and 
three  small  cells  or  polar  bodies  (incapable  of  fertilization),1 
which  take  no  part  in  the  further  development,  are  discarded, 
and  soon  die  without  further  change.  The  egg  nucleus  (of  the 
ovum  proper)  is  now  ready  for  union  with  the  sperm  nucleus,2 
which  process  is  known  as  fertilization. 

"  In  some  cases — for  example  in  the  sea  urchin  — the  polar 
bodies  are  formed  before  fertilization,  while  the  egg  is  still  in 

tetrad  form  is  always  chosen  for  description  because  the  details  are  capable  of 
more  definite  statement.  Whatever  the  form  of  the  masses,  however,  the  final 
result  seems  always  the  same  ;  namely,  a  reduction  to  one  half  the  usual  number 
of  chromosomes,  and  this  by  the  method  of  division  and  extrusion. 

1  In  rare  instances  the  polar  bodies  have  commenced  to  segment,   but  they 
never  proceed  far  in  development. 

2  Wilson,  The  Cell,  pp.  236-237. 


E  H 

FIG.  24.    Diagrams  showing  the  essential  facts  in  the  maturation  of  the  egg. 
The  somatic  number  of  chromosomes  is  supposed  to  be  four 

A,  initial  phase:  two  tetrads  have -been  formed  in  the  germinal  vescicle.  £,  the  two 
tetrads  have  been  drawn  up  about  the  spindle  to  form  the  equatorial  plate  of  the  first 
polar  mitotic  figure.  C,  the  mitotic  figure  has  rotated  into  position,  leaving  the  remains 
of  the  germinal  vesicle  at  g.v.  D,  formation  of  the  first  polar  body :  each  tetrad 
divides  into  two  dyads.  £,  first  polar  body  formed:  two  dyads  in  it  and  also  in  the 
egg  (A'*-1)-  ^  preparation  for  the  second  division.  G,  second  polar  body  forming  and  the 
first  dividing:  each  dyad  divides  into  two  single  chromosomes.  //,  final  result:  three 
polar  bodies  and  the  mature  ovum,  each  containing  two  single  chromosomes,  or  half 
the  somatic  number ;  c,  the  egg  centrosome,  which  now  degenerates  and  is  lost.  —  After 
Wilson 

168 


INTERNAL  CAUSES  OF  VARIATION  160 

••       ••        ••»  ^ 

the  ovary.  More  commonly,  as  in  annelids,  gasteropods,  and 
nematodes,  they  are  not  formed  until  after  the  spermatozoon 
has  made  its  entrance  ;  while  in  a  few  cases  one  polar  body 
may  be  formed  before  fertilization  and  one  afterward,  as  in  the 
lamprey  eel,  the  frog,  and  in  Amphioxiis.  In  all  these  cases 
the  essential  phenomena  are  the  same.  Two  minute  cells  are 
formed,  one  after  the  other,  in  rapid  succession  and  near  the 
upper  or  animal  pole  of  the  ovum ;  and  in  many  cases  the  first 
of  these  divides  into  two  as  the  second  is  formed." 

To  what  extent  this  division  is  qualitative  is  unknown.  Of 
one  thing  we  are  certain  :  somewhere  in  the  process  the  number 
of  chromosomes  has  been  reduced  to  exactly  one  half  the  number 
characteristic  of  the  species. 

It  was  formerly  supposed  by  Van  Beneden,  Weismann,  and 
Boveri  that  reduction  consists  in  the  casting  out  and  degenera- 
tion of  half  of  the  chromosomes.  "  Later  researches  conclusively 
showed,  however,  that  this  view  cannot  be  sustained,  and  that 
reduction  is  effected  by  a  rearrangement  and  redistribution  of  the 
nuclear  substance,  without  loss  of  any  of  its  essential  constitu- 
ents." 1  This  is  said  because  the  groups  —  tetrads,  rods,  rings, 
etc.  — arise  spontaneously  in  the  nucleus  in  the  reduced  number. 
The  loss  occurs  later  in  the  extrusion  of  the  polar  bodies,  but 
no  corresponding  loss  takes  place  on  the  male  side  because  all 
four  cells  are  functional,  though  not  all  alike. 

Reduction  in  the  male.2  The  maturation  processes  in  the  male 
and  female  are  practically  identical  in  their  results,  with  two 
exceptions ;  namely,  first,  in  the  male  the  four  cells  resulting 
from  the  maturation  divisions  are  all  alike  functional,  and  second, 
they  are  exceedingly  small  in  size  as  compared  with  the  ovum, 
being  almost  destitute  of  cytoplasm. 

The  spermatogonia,  corresponding  to  the  oogonia  of  the 
female,  arise  in  the  testes  by  mitotic  division,  with  the  full 
somatic  number  of  chromosomes.  As  in  the  female,  they  reach 
a  stage  where  division  ceases  for  a  time  and  enlargement  ensues, 
in  which  condition  the  cells  are  known  as  spermatocytes  (corre- 
sponding to  oocytes  in  the  female). 

1  Wilson,  The  Cell,  p.  233. 

2  Ibid.  pp.  241-242. 


1 70  CAUSES  OF  VARIATION 

At  the  proper  stage  each  spermatocyte  undergoes  two  divi- 
sions (maturation  divisions)  into  four  cells,  called  spermatids, 
each  of  which  develops  a  tail  and  becomes  functional,  in  which 
finished  condition  it  is  known  as  a  spermatozoon,  when  it  is 
ready  to  enter  and  fertilize  the  ripened  ovum. 

The  history  and  distribution  of  the  chromatin  matter  in  the 
male  is  identical  with  that  in  the  female,  so  that  each  sperma- 
tozoon inherits  one  fourth  the  chromatin  matter  and  one  half  tJie 
chromosomes  of  the  original  cell.  In  plants  the  process  differs 
but  the  general  results  are  the  same. 

Significance  of  reduction.  On  the  female  side  three  fourths  of 
the  chromatin  matter  has  been  extruded  in  the  polar  bodies,  and 
therefore  lost  to  the  line  of  descent.  Whether  reduction  takes 
place  by  extrusion  or  by  rearrangement,  one  thing  is  certain  : 
when  the  second  division  is  transverse,  and  possibly  when  it  is 
longitudinal,  it  results  in  an  unequal  division  of  physiological 
units,  if  the  identity  of  the  chromosomes  and  the  chromatin 
granules  has  any  meaning.  If  this  division  be  anything  else 
than  strictly  qualitative,  then  the  extrusion  of  the  polar  bodies 
means  a  loss  of  something  qualitative  on  the  female  side. 

On  the  male  side  the  loss  is  not  absolute,  because  all  four 
cells  are  functional,  but  if  reduction  has  the  -meaning  we  attach 
to  it,  these  four  spermatozoa  are  not  identical  but  different  in 
the  hereditary  substance  with  which  they  are  provided. 

Significance  of  fertilization.  Here,  then,  are  two  sexual  cells 
ready  for  union.  Each  has  lost  large  portions  of  its  chromatin 
matter,  the  evident  vehicle  of  transmission,  and  each  brings  to 
the  union  but  one  half  the  number  of  chromosomes  characteris- 
tic of  its  species,  strongly  suggesting  a  loss  of  certain  chromatin 
granules  and  the  hereditary  qualities  they  represented. 

When  fusion  of  the  nuclei  of  these  two  germ  cells  takes  place 
at  fertilization,  however,  the  act  of  union  again  restores  the  full 
and  proper  number  of  chromosomes,  which  will  remain  charac- 
teristic of  the  new  individual  throughout  its  life,  and  which  it 
will  hand  down  to  posterity,  always  through  the  same  compli- 
cated method  we  have  attempted  to  describe.  The  number  of 
chromosomes  is  evidently  kept  constant  by  the  complicated 
process  of  reduction  during  maturation  and  by  fertilization 


INTERiNAL  CAUSES  OF   VARIATION  171 

afterward  ;  but  what  about  their  character  ?  In  what  condition 
have  they  emerged  from  this  seemingly  incomprehensible  tangle  ? 
Is  nature  as  careful  to  preserve  their  quality  as  it  is  their  number  ? 

What  opportunities  for  profound  variation !  Certainly  if 
chromatin  matter  has  any  fundamental  meaning,  and  if  chromo- 
somes are  in  any  way  representative  of  physiological  units, 
and  if  they  in  their  turn  are  in  any  way  representative  of  racial 
characters,  these  processes  must  have  some  meaning  in  varia- 
tion. Certainly  we  have  been  very  near  in  all  this  to  the  material 
basis  of  transmission  of  racial  characters,  and  to  fundamental  and 
initial  causes  of  variation. 

Something  has  been  lost  in  the  two  peculiar  divisions  attend- 
ing maturation.  Some  definite  groupings  of  hereditary  substance 
have  disappeared  from  the  line  of  descent.  They  could  not  have 
represented,  ordinarily,  definite  portions  of  a  body,  but  they  must 
represent  something.  What  chances  for  accident !  And,  in  the 
light  of  these  marvelous  phenomena,  do  we  wonder  that  individ- 
uals are  sometimes  born  minus  a  leg,  an  arm,  or  some  other  part  ? 
Do  we  wonder  that  vital  parts  are  so  often  affected,  and  that  one 
third  of  our  children  die  in  infancy  ?  How  many  die  before  birth, 
and  how  many  more  die  at  some  stage  in  embryo ! 

Evidently  all  that  is  required  to  make  a  living  being  is  a 
fairly  perfect  development  of  the  vital  parts,  quite  regardless  of 
the  presence  or  absence  of  the  many  other  racial  characters 
that  should  be  present  in  the  perfect  individual.  Is  it  surprising 
that  perfect  individuals  are  so  few,  and  that  defectives  are 
frequently  so  far  from  the  type  ?  Here  is  material  for  study 
on  the  part  of  criminologists  and  courts  of  justice,  as  well  as 
students  of  methods  of  economic  improvement. 

Reduction  and  fertilization  in  plants.  It  may  be  said  in 
general  that  in  animals  the  evidence  tends  to  the  assumption 
that  reduction  takes  place  at  the  extrusion  of  the  second  polar 
body  ;  that  each  group  (rod,  ring,  or  V-shaped  body)  is  in  reality 
a  doubled  (bivalent)  chromosome,  and  that  the  first  polar  body 
removes  one  half  of  each  (split)  chromosome,  while  the  next 
removes  every  alternate  chromosome. 

While  the  facts  of  reduction  in  plants  are  not  yet  fully  worked 
out,  it  is  safe  to  say  that  the  evidence  tends  to  show  that  no 


172 


CAUSES  OF  VARIATION 


true  polar  bodies  are  formed,1  but  that  the  chromosomes  sud- 
denly appear  in  reduced  number  at  the  first  division,  which 
results  in  four  daughter  cells,  any  one  or  all  of  which  may  be 
functional,  according  to  the  species.  It  is  not  the  purpose  here 
to  discuss  the  detailed  behavior  of  various  plant  forms  in  matu- 
ration. It  is  sufficient  to  say  that  botanists  recognize  two  stages 
in  the  development  of  the  female  germ  cell  of  the  plant,  neither 
of  which  is  identical  with  maturation  in  animals,  though  the  first 
is  fairly  comparable  thereto.  The  first  stage,  or  sporogenesis, 
follows  after  that  active  massing  of  food  material  which  marks, 
in  both  plant  and  animal,  the  preparation  for  reduction.  At  this 
time  the  nucleus  divides  quickly  into  four  daughter  nuclei,  each 
of  which  is  supplied  with  half  the  number  of  chromosomes  that 
characterizes  the  species.  The  significant  fact  is  that  reduction 
is  accomplished  at  this  stage. 

Of  these  four  daughter  nuclei  none  are  extruded,  but  three 
of  them  degenerate  in  the  cytoplasm,  while  the  fourth  increases 
in  size  to  form  the  embryo  sac,  which,  without  waiting  for  ferti- 
lization as  among  animals,  continues  to  divide,  —  commonly 
three  times,  —  giving  rise  to  eight  sub-nuclei,  which  arrange 
themselves  in  definite  positions.  Two  of  these  sub-nuclei  re- 
main near  the  center  of  the  embryo  sac  and  give  rise  to  the 
endosperm  ;  three  migrate  to  the  extremity  nearest  the  point 
of  attachment  with  the  pistil,  and  one  of  these  (and  one  only) 
—  the  so-called  egg  nucleus  —  unites  with  the  nucleus  of  the 
pollen  grain  to  form  the  fertilized  germ  ;  the  three  remaining 
migrate  to  the  other  extremity  of  the  embryo  sac  and  concern 
themselves  with  establishing  a  food  supply  with  the  parent  plant. 

On  the  male  side  the  process  is  simpler.  The  pollen  nucleus 
divides,  one  half  forming  the  pollen  tube,  along  which  the  other 
half  travels,  dividing  again  at  some  point  before  uniting  with  the 
egg  nucleus  of  the  embryo  sac.  These  divisions  are  evidently 
not  reducing  divisions,  as  reduction  occurs  previously  during 
the  division  of  the  pollen  mother  cell. 

1  Disputed  by  Chamberlain,  who  believes  that  "the  egg  with  its  three  polar 
bodies  constitutes  a  generation  directly  comparable  with  the  gametophytic  genera- 
tion in  plants."  See  Botanical  Gazette,  XXXIX,  139;  see  also  under  "  Xenia,"  in 
this  text. 


INTERNAL  CAUSES  OF  VARIATION  173 

Thus,  while  the  plan  is  different  in  plants  and  in  animals,  the 
first  stage,  sporogenesis,  in  plants  seems  fully  comparable  with 
maturation  in  animals,  and  the  same  general  end  is  accomplished.1 

After  all,  the  manner  of  division  is  primarily  of  interest  to 
the  physiologist  and  does  not  concern  us.  Our  interest  is  in 
the  fact  that  maturation  in  general  involves  an  actual  loss  of 
chroinatin  matter  (hereditary  substance)  and  a  reduction  in  the 
number  of  chromosomes ;  and  consequently  of  physiological  units. 
In  the  present  state  of  knowledge  it  seems  safe  to  assume  that 
both  these  results  follow,  whatever  the  mechanism  of  maturation 
in  each  particular  instance.  If  this  be  true,  here  is  a  fertile  and 
initial  cause  of  profound  variation,  an  excellent  opportunity  for 
losing  important  elements  of  the  physical  make-up,  but,  so  far 
as  we  can  see,  no  chance  for  positive  gain,  unless  it  be  by  new 
combinations,  because  nothing  is  introduced. 

Phenomena  such  as  these  are  remarkable  for  what  they  sug- 
gest rather  than  for  conclusions  that  can  be  positively  drawn. 
The  suggestion  is  that  of  substantial  deviation  in  the  very  fun- 
damental process  of  transmission  of  the  hereditary  substance,  — 
a  deviation  that  cannot  but  be  fruitful  of  variation  in  resulting 
individuals. 

Weismann's  prediction.  It  is  noteworthy  that  reduction  was 
predicted  by  Weismann  on  purely  theoretical  grounds  some 
years  before  it  was  known  as  a  fact.2  He  argued  for  its  recur- 
rence as  a  physiological  necessity  to  prevent  the  piling  up  of 
"  ancestral  idioplasm," — the  physiological  units  to  which  he 
afterward  gave  the  name  of  "  ancestral  units,"3  —  and  later 
developed  the  intricate  system  of  biophors,4  determinants,5  ids,0 
and  idants,6  by  virtue  of  which  he  explained  the  constitution  of 
the  germ  plasm,7  and  which  he  used  as  the  basis  for  his  famous 
theories  of  heredity.8 

1  For  full  discussion,  see  articles  by  B.  M.  Davis,  American  Naturalist,  XXXIX, 
Nos.  460  and  463. 

2  Weismann,  Essays  on  Heredity,  I,  357,  363-396;  II,   114-150;  also  Weis- 
mann, The  Germ  Plasm,  chap.  viii.         3  Weismann,  Essays  on  Heredity,  II,  116. 

4  Weismann,  The  Germ  Plasm,  pp.  40-53.  5  Ibid.  pp.  53-60. 

6  Weismann,  Essays  on  Heredity,  II,  136-138;  Weismann,  The  Germ  Plasm, 
PP-_6o-75. 

7  Weismann,  The  Germ  Plasm,  chap,  i,  pp.  37-85. 
s  Ibid.  chap,  ix,  pp.  253-293. 


I74  CAUSES  OF  VARIATION 

The  later  discovery  of  the  mechanism  of  maturation  and  of 
the  extrusion  of  the  polar  bodies  was  a  startling  confirmation  of 
Weismann's  prediction,  and  went  far  to  fix  his  theories  of  hered- 
ity in  the  minds  of  many  biologists.  In  this  connection  Wilson 
very  pertinently  remarks  : 1 

The  fulfillment  of  Weismann's  prediction  is  one  of  the  most  interesting 
results  of  recent  cytological  research.  It  has  been  demonstrated  in  a  manner 
which  seems  to  be  incontrovertible  that  the  reducing  divisions  postulated 
by  Weismann  actually  occur,  though  not  precisely  in  the  manner  conceived 
by  him,  .  .  .  but  it  remains  quite  an  open  question  whether  they  have  the 
significance  attributed  to  them  by  Weismann. 

Just  when  the  reduction  occurs  is  not  known.  It  was  at  first 
assumed  that  it  occurs  in  connection  with  the  extrusion  of  the 
second  polar  body,  —  an  assumption  based  upon  the  development 
of  parthenogenetic  eggs.  But  plants  do  not  form  polar  bodies, 
and  again  there  is  great  uncertainty  as  to  whether  the  rods 
(tetrads),  rings,  or  V-shaped  bodies  (whose  number  is  half  the 
usual  number  of  chromosomes)  are  to  be  regarded  as  represent- 
ing the  usual  number  of  chromosomes  split  and  arranged  in 
pairs,  —  in  which  case  the  second  polar  body  would  accomplish 
the  reduction ;  or  whether  the  chromosomes  as  formerly  known 
never  emerge  from  the  nucleus  of  the  oocyte,  so  that  the  iden- 
tity of  the  chromosomes  is  in  some  way  lost  and  the  reduction 
is  effected  at  this  early  stage  by  some  sort  ,of  internal  fusing,  or 
perhaps  by  an  entire  rearrangement  of  chromatin  granules.  On 
this  point  the  evidence  is  confusing,  but  on  two  significant 
points  there  is  no  doubt,  —  the  loss  of  chromatin  matter  out  of 
the  line  of  descent,  and  a  reduction  of  the  chromosomes  in  the 
germ  cells  to  one  half  the  somatic  number.2 

Composition  of  the  chromosomes.3  In  view  of  the  important 
office  of  the  chromosomes  and  the  many  theories  of  heredity 
based  upon  their  nature  and  constitution,  in  view  also  of  their 
evident  importance  in  all  studies  on  inheritance  and  variation, 

1  Wilson,  The  Cell,  p.  246. 

2  By  "somatic"  number  is  meant  the  number  characteristic  of  the  soma, — 
the. body  in  general  as  distinct  from  the  germinal  matter  whose  function  is  not 
growth  but  reproduction. 

8  Wilson,  The  Cell,  pp.  294-304. 


INTERNAL  CAUSES  OF  VARIATION  175 

it  may  be  well  to  note  the  substance  of  what  is  really  known 
about  their  actual  constitution. 

That  they  are  not  masses  of  homogeneous  matter  is  certain, 
and  that  they  consist  of  numbers  of  small  granules  capable  of 
multiplication  and  division  seems  equally  certain.  To  quote 
Wilson : 

The  facts  are  now  well  established  (i)  that  in  a  large  number  of  cases 
the  chromatin  thread  consists  of  a  series  of  granules  (chromomeres) 
imbedded  in  and  held  together  by  the  linin  substance  ;  (2)  that  the  split- 
ting of  the  chromosomes  is  caused  by  the  division  of  these  more  elementary 
bodies ;  (3)  that  the  chromatin  grains  may  divide  at  the  time  when  the 
spireme  is  only  just  beginning  to  emerge  from  the  reticulum  or  resting 
stage. 

Because  of  these  facts  there  arises  the  strongest  tendency  to 
attach  individuality  to  the  chromatin  granules  and  to  conceive 
them  as  built  up  of  definite,  though  often  diverse,  physiological 
units,  thus  constituting  a  semi-mechanical  basis  for  heredity,  and 
incidentally  for  variation  as  well.  This  assumption  Weismann 
and  others  have  made.  Whether  the  facts  should  be  pushed  to 
this  extreme  interpretation  is,  in  the  opinion  of  the  author,  as 
yet  uncertain.  The  facts  are  extremely  suggestive,  to  say  the 
least,  and  it  is  certainly  not  too  much  to  believe  that  at  this 
point  we  have  touched  the  physical  basis  of  life  and  in  some 
fashion  the  very  root  of  inheritance  and  variation  ;  indeed  we 
may  proceed  upon  the  conviction  that  transmission  is  a  function 
of  the  chromatin  granules. 

Reduction  as  a  cause  of  variation.  The  most  remarkable  and 
suggestive  fact  about  living  beings  is  the  numerical  constancy 
of  chromatin  units  (chromosomes)  for  each  species,  and  the 
most  remarkable  and  suggestive  of  all  the  vital  processes  is 
their  reduction  before  fertilization.  If,  as  we  suppose,  the 
chromosomes  are  the  physical  basis  of  inheritance,  then  in  the 
loss  of  chromatin  matter  at  maturation  lies  a  fimdamental  cause 
of  variation,  and  one  quite  independent  of  the  effects  of  fertili- 
zation afterward. 

Reduction  would  seem  to  be  a  process  calculated  to  insure 
that  no  two  germ  cells,  even  from  the  same -individual,  should 
ever  be  alike,  and  this  is  the  most  evident  reason  for  the 


!76  CAUSES  OF  VARIATION 

essential  differences  in  children  of  the  same  parents,  even  in 
the  case  of  twins.1 

It  is  true,  of  course,  that  no  two  individuals,  even  twins,  can 
be  developed  under  conditions  of  life  exactly  identical  ;  and  yet 
the  differences  of  condition  cannot  account  for  the  fact  that, 
while  one  brother  resembles  his  father,  another  may  resemble 

1  Twins  are  considered  as  arising  from  separate  ova,  as  in  the  case  of  multiple 
births  (pigs,  dogs,  etc.),  and,  of  course,  as  exhibiting  the  deviations  to  be  expected 
from  different  germs  and  distinct  fertilization,  as  in  litters  generally. 

Some  twins,  however,  are  so  nearly  alike  (identical  twins)  as  to  suggest  the 
possibility  of  their  having  arisen  from  a  single  ovum  in  some  way  separated  into 
halves  at  its  first  cleavage,  each  half  developing  an  individual.  This  view  is 
evidently  favored  by  Geddes  and  Thomson  (see  The  Evolution  of  Sex,  p.  41). 

If  twins  should  be  developed  in  this  manner,  they  would  evidently  be  of  the 
nearest  possible  similarity,  for  they  represent  but  one  ovum  and  but  a  single 
fertilization. 

This  possibility  is  supported  by  the  experiments  of  Roux,  Endres,  and  Walter, 
in  which  each  blastomere  of  the  two-cell  stage  of  the  frog  sometimes  (not  always) 
is  capable  of  developing  into  a  perfect  individual.  Driesch,  working  with  echino- 
derms,  established  the  same  facts,  which  are  also  well  known  in  the  case  of 
Amphioxtts  (see  Wilson,  The  Cell,  p.  419). 

Conversely,  when  two  fertilized  ova  of  sea  urchin,  or  Ascaris,  adhere  acci- 
dentally, they  may  develop  into  an  embryo  of  unusual  dimensions  (see  Loeb, 
Studies  in  General  Physiology,  Part  II,  p.  676). 

When,  however,  the  blastomeres  are  not  separated,  but  one  of  them  is  killed 
by  a  heated  needle  (Roux),  the  uninjured  half  alone  develops,  but  it  produces 
at  the  best  a  kind  of  half  larva  (right  or  left  half),  "  containing  one  medullary 
fold,  one  auditory  pit "  (Wilson,  The  Cell,  p.  399).  Chun,  Driesch,  Morgan,  and 
Fischel,  working  with  ctenophore  eggs,  however,«found  that  isolated  blastomeres 
of  the  two-,  four-,  or  eight-cell  stages  developed  "  defective  larvae,  having  only 
four,  two,  or  one  row  of  swimming  plates."  Also  "  Crampton  found  that  in  the 
case  of  the  marine  gasteropod  llyanassa  isolated  blastomeres  of  two-cell  or  four- 
cell  stages  segmented  exactly  as  if  forming  part  of  an  entire  embryo,  and  gave  rise 
to  fragments  of  a  larva,  not  to  complete  dwarfs  as  in  the  echinoderm"  (Wilson, 
The  Cell,  p.  419).  This  attempt  to  form  entire  individuals  from  a  portion  only 
of  a  fertilized  egg,  resulting  as  it  often  does  in  dwarfs,  seems  to  the  writer  a 
process  closely  akin  to  regeneration  (which  see  in  chapter  on  "  Relative  Stability 
and  Instability  of  Living  Matter"),  and  would  seem  to  raise  doubts  as  to  its 
successful  occurrence  in  the  higher  animals. 

Though  not  bearing  especially  upon  the  point  in  question,  the  matter  of  twins 
in  cattle  is  unique  and  worthy  of  mention.  Three  kinds  of  twins  are  known  in 
cattle:  "  (i)  the  twins  may  be  both  female  and  both  normal;  0^(2)  the  sexes 
may  be  different  and  norm'al ;  or  (3)  both  may  be  males,  in  which  case  one  always 
exhibits  the  peculiar  abnormality  known  as  a 'free-martin,'  —  the  internal  organs 
are  male,  but  the  external  accessory  organs  are  female,  and  there  are  also  rudi- 
mentary female  ducts."  (Geddes  and  Thomson,  The  Evolution  of  Sex,  p.  41). 
This  is  a  kind  of  hermaphroditism,  and  not,  as  is  commonly  supposed,  "a  heifer 
twin  with  a  bull." 


INTERNAL  CAUSES  OF  VARIATION  177 

his  mother  or  one  of  her  male  ancestors.  Differences  such  as 
these  must  arise  from  strictly  internal  causes,  which  seem  to  set 
a  natural  and  inevitable  limit  to  what  may  be  accomplished 
through  selection.  Here  would  seem  to  be  an  irreducible  mini- 
mum in  variation,  arising  directly  through  reduction.1 

Control.  In  so  far  as  variations  arise  through  changes  in 
hereditary  matter  during  the  processes  of  maturation  and  reduc- 
tion, they  are,  and  must  doubtless  always  remain,  entirely 
beyond  the  influence  of  the  breeder.  It  is  quite  evident  that 
here  is  a  degree  of  deviation  and  an  element  in  breeding  that 
must  be  left  to  nature  and  subject  to  the  laws  of  chance  within 
the  range  of  characters  natural  to  the  race.  That  this  will  always 
be  a  bar  to  absolute  success  is  evident,  but  that  it  constitutes 
the  strongest  known  argument  for  purity  of  blood  is,  in  the 
opinion  of  the  writer,  beyond  question,  because  the  chances  of 
unfortunate  deviations  are  reduced  in  proportion  to  the  purity  of 
blood  and  the  absence  of  undesirable  characters. 

Variation  in  parthenogenetic  reproduction.2  Had  Weismann's 
original  assumption  been  correct  to  the  effect  that  sexual  union 
is  the  only  constitutional  cause  of  variation,  then  individuals 
arising  from  parthenogenetic  reproduction  should,  barring  the 
influence  of  surrounding  conditions,  be  alike,  because  only  the 

1  Endeavoring  to  determine  the  function  of  the  cytoplasm  and  nucleus,  Boveri 
removed  the  nuclei  from  the  eggs  of  sea  urchins  and  afterward  admitted  sperma- 
tozoa to  these  enucleated  ova.    Development  followed  in  a  few  cases,  but  the 
nuclei  were  smaller  than  in  larvae  normally  fertilized,  contained  but  half  the  num- 
ber of  chromosomes,  and  the  resulting  larvae  possessed  the  "pure  parental  characters." 

It  is  not  supposable  that  anything  like  this  occurs  in  nature,  and  yet  it  raises 
the  question  whether,  after  reduction,  every  remaining  element  of  the  nucleus  of 
both  parents  always  plays  its  part  in  development.  Should  it  fail  to  do  so  for  any 
reason,  herein  would  lie  a  sufficient  cause  for  the  occasional  remarkable  resem- 
blance of  offspring  to  one  and  not  the  other  parent. 

2  While  in  all  higher  animals  and  plants  a  union  of  a  male  with  the  female  cells 
is  necessary  to  each  fertilization  and  to  the  production  of  young,  it  is  by  no  means 
true  among  other  organisms,  especially  in  rotifers,  crustaceans,  and  insects  with 
which  "parthenogenesis  has  become  a  fixed  physiological  habit,"  through  which 
the  unfertilized  female  cell  develops  a  perfect  individual. 

It  is  now  well  known  that  the  queen  of  the  honeybee,  if  prevented  from  mat- 
ing, will  yet  lay  eggs  capable  of  development,  but  they  will  all  be  drones  (males). 
After  mating  she  can  lay  either  fertilized  or  unfertilized  eggs,  the  fertilized  devel- 
oping into  workers  (undeveloped  females), —  or,  if  properly  fed,  into  queens, — 
the  unfertilized  into  drones  as  before.  After  the  male  element  is  exhausted  (she 


1 78  CAUSES  OF  VARIATION 

female  and  her  germ  cell  are  involved.  But  individuals  thus 
arising  through  unisexual  reproduction  vary  ividely,  a  fact  easily 
credited  when  the  phenomena  of  reduction  are  remembered. 

Parthenogenesis  being  limited  to  lower  animals,  the  range  and 
character  of  variations  are  for  the  most  part  difficult  of  detection 
and  measurement.  It  is  known,  however,  that  great  differences 
in  size  occur  among  individuals  parthenogenetically  produced, 
and  characters  generally  are  so  variable  in  such  individuals 
as  to  lead  to  the  statement  that  the  variability  of  offspring 

never  mates  but  once)  she  is,  of  course,  capable  of  laying  only  unfertilized  or  "  drone 
eggs."  In  this  way,  in  crossing,  the  drones  and  the  workers  may  actually  be  of 
different  breeds. 

Plant  lice  reproduce  parthenogenetically  during  the  summer  season,  producing 
only  females  ;  but  as  the  temperature  lowers  with  approaching  autumn  a  mixed 
brood  of  both  males  and  females  appears,  which,  upon  mating,  produces  the  long- 
lived,  winter-enduring  eggs.  It  is  noteworthy  that  the  parthenogenetic  eggs  of 
bees  develop  males  only,  while  those  of  plant  lice  develop  females  during  the 
summer,  both  sexes  appearing  as  autumn  approaches. 

It  is  also  noteworthy  that  under  the  artificial  heat  of  greenhouses,  approximat- 
ing perpetual  summer  conditions,  parthenogenesis  continues  indefinitely,  and  males 
are  not  produced  unless  the  plants  become  badly  dried  up. 

Parthenogenesis  differs  greatly  in  degree.  It  is  supposed  to  be  complete  in 
certain  minute  crustaceans  and  in  many  rotifers  among  which  "  no  males  have  ever 
been  found."  It  is  "seasonal"  in  the  aphis  (plant  lice),  and  "partial"  in  the 
honeybee  and  "  in  some  of  the  lower  animals  which  are  not  themselves  normally 
parthenogenetic,  but  have  relatives  which  are."  Occasional  parthenogenesis  has 
been  frequently  observed.  An  example  is  the  silk  moth,  in  which  Nussbaum 
found  that  out  of  1 102  unfertilized  eggs  ...  22  developed  ...  up  to  a  certain 
point.  It  is  supposed  that  in  all  cases  of  parthenogenesis  many  eggs  fail  to  develop. 

In  this  connection  it  is  noteworthy  and  extremely  suggestive  that  among  higher 
animals — frogs,  hens,  and  even  mammals  —  the  unfertilized  ovum  occasionally 
begins  segmentation,  never  proceeding  far,  however,  on  its  parthenogenetic  course. 

The  student  should  understand  that  in  all  probability  a  large  number  of  eggs 
fail  to  develop  into  complete  individuals  even  in  the  most  successful  parthen- 
ogenesis, just  as  do  many  fertilized  ova  fail  along  the  way  (see  Weismann,  Essays 
on  Heredity,  I,  175).  There  are  all  degrees  of  parthenogenesis,  from  the  perfectly 
successful  down  to  zero. 

Bearing  upon  the  general  subject  are  the  interesting  experiments  of  Loeb  in 
artificial  parthenogenesis,  especially  of  the  sea  urchin,  normally  bisexual,  but  which, 
after  immersion  in  a  saline  solution  of  high  density  and  subsequent  return  to  nor- 
mal sea  water,  commenced  segmentation  and  afterward  developed  living  larvae. 
Magnesium  and  potassium  salts  proved  most  effective,  though  in  general  any 
treatment  avails  that  serves  to  withdraw  a  portion  of  the  water  from  the  unfertilized 
egg  (see  Loeb  in  American  Journal  of  Physiology,  III,  434;  also  Loeb,  Studies 
in  General  Physiology,  Part  II,  pp.  576-626,  638-692;  Methods,  pp.  766-772; 
Geddes  and  Thomson,  Evolution  of  Sex,  pp.  183-198). 


INTERNAL  CAUSES  OF  VARIATION  179 

asexually  reproduced  is  not  ''immensely  reduced  below  the  vari- 
ability of  the  race."  1 

In  the  honeybee  only  the  male  sex  is  produced  parthenoge- 
netically.  In  plant  lice  it  is  commonly  the  female  alone  under 
high  temperature,  and  both  sexes  under  lower.  Weismann  bred 
separately  two  varieties  of  Cypris  reptans  for  some  seven  years, 
covering  more  than  forty  generations  and  "  many  thousand  indi- 
viduals." One  variety,  A,  was  light  in  color;  the  other,  B,  was 
dark.  No  males  were  ever  discovered  in  either,  and  it  is  sup- 
posed that  this  species  produces  only  parthenogenetically.  While, 
for  the  most  part,  the  descendants  of  each  were  extremely  alike, 
yet  "  minute  differences  invariably  existed." 

Not  only  was  this  true,  but  in  1887,  three  years  after  the 
experiment  commenced,  "  some  individuals  of  the  dark  green 
variety,  B,  appeared  in  the  aquarium  with  the  light  variety." 
The  same  variation  appeared  a  second  and  a  third  time,  and  in 
the  last  instance  intermediate  forms  could  be  made  out.  In 
1891  another  case  occurred,  and  in  the  same  year  its  converse 
appeared, — a  few  typical  light  individuals  among  the  dark 
colony  that  had  "bred  true  many  years."2  Does  this  experi- 
ment also  throw  light  on  the  origin  of  varieties,  and  were  these 
mutations  ?  However  this  may  be,  it  clearly  shows  that  vari- 
ability is  not  entirely  dependent  upon  sexual  union,  and  that 
even  distinct  varieties  may  arise  without  the  intervention  of  sex. 

The  first  significant  fact  in  maturation  of  parthenogenetic 
eggs  is  that  they  produce  but  one  polar  body.3 

From  this  point  on  two  alternatives  seem  possible.  In  the 
first  place,  a  second  polar  body  appears  to  be  forming  in  the 
usual  manner  and  the  separation  of  the  nuclear  matter  takes 
place,  but  instead  of  passing  out  of  the  egg  it  remains  behind, 
fusing  again  with  the  nucleus  of  the  egg  proper,  which  straight- 
way undergoes  development,  with  its  chromosomes  increased  to 

1  Pearson,  Grammar  of  Science,  pp.  472-473. 

2  Weismann,  Essays  on  Heredity,  I,  161-164. 

3  Often  this  polar  body  divides,  giving  the  appearance  of  two,  but  a  second  one 
is  not  formed.    It  is  quite  remarkable,  though  entirely  consistent,  in  the  case  of 
aphis,  honeybees,  and  certain  other  forms  that  produce  both  sexually  and  asexu- 
ally, that  \\\Q  fertilized  eggs  produce  two  polar  bodies  but  the  parthenogenetic  eggs 
only  one. 


CAUSES   OF  VARIATION 

the  proper  number.  In  this  case  the  second  polar  body  appears 
in  the  role  of  a  male  element,  so  we  may  speak  of  this  as  a  kind 
of  "fertilization  by  the  second  polar  body!' 

In  the  other  form  of  parthenogenesis,  however,  there  is  little 
suggestion  of  a  second  polar  body ;  certainly  no  formal  separa- 
tion and  later  fusing  of  nuclear  matter  takes  place.  On  the  con- 
trary, development  takes  place  directly  upon  the  extrusion  of 
the  first  polar  body,  and  it  is  significant  that  individuals  arising 
in  this  way  possess  but  half  the  number  of  chromosomes  as  com- 
pared with  those  arising  by  sexual  reproduction  or  by  the  method 
just  described.  Some  species  (as  in  Artemia) :  reproduce  par- 
thenogenetically  by  both  methods,  giving  rise  to  two  distinct 
varieties,  one  with  half  the  number  of  chromosomes  character- 
istic of  the  other.2 

Mutation  as  related  to  reduction  and  fertilization.  Mutants 
seem  to  be  departures  characterized  by  a  sudden  loss  of  some 
racial  character  or  by  its  possession  in  some  unusual  degree. 
They  do  not  appear  to  be  endowed  with  characters  new  to  the 
race,  except  when  artificially  produced  by  hybridization. 

If  the  process  of  reduction  means  the  loss  of  hereditary 
material,  and  if  fertilization  means  its  restoration,  and  if  either 
means  in  any  sense  new  combinations,  then  we  can  see  in  the 
two  phenomena  taken  together,  or  even  singly,  abundant  oppor- 
tunity for  the  most  profound  variations  ;  indeed,  admitting  their 
possibility  through  these  causes,  the  wonder  is  that  they  are  not 
yet  more  common  and  infinitely  more  remarkable. 

If  there  is  in  any  sense,  however  slight,  a  qualitative  loss 
through  reduction,  then  by  the  law  of  chance  the  time  is  certain 
to  come  when  something  unusual  will  appear.  Is  it  not  more 
than  likely  that  here  lies  a  fruitful  source  of  sweeping  changes, 
as  well  as  of  the  more  obscure  differences  that  are  everywhere 
about  us  ?  And  is  it  not  likely  that  still  greater  and  more  fre- 
quent changes  would  present  themselves  were  it  not  that  fertili- 
zation is  for  the  most  part  restricted  to  comparatively  narrow 
lines  ? 

1  Wilson,  The  Cell,  pp.  282-283. 

3  Artemia  thus  varies  from  84  to  168,  according  to  the  particular  method 
observed. 


INTERNAL  CAUSES  OF  VARIATION  181 

SECTION   IV  — BUD   VARIATION1 

Variation  is  not  necessarily  connected  with  reproduction  in 
the  ordinary  sense  of  the  term.  One  limb  of  a  peach  may  pro- 
duce nectarines.  A  single  branch  of  a  tree  may  assume  the 
weeping  habit  or  the  cut-leaved  form.  Not  only  are  these  wide 
deviations  between  buds  of  the  same  tree  well  established,  but 
also  all  shades  of  differences  exist,  showing  that  one  part  of  a 
plant  may  vary  independently  of  another,  quite  after  the  manner 
of  meristic  variation  among  animals. 

Bailey2  calls  attention  to  the  fact  that  the  plant  is  not 
an  individual  with  a  simple  anatomy  like  an  animal,  but  that 
"  its  parts  are  virtually  independent  in  respect  to  (i)  propaga- 
tion, ...  (2)  struggle  for  existence  among  themselves,  (3)  varia- 
tion, (4)  transmission  of  their  characters  by  means  of  either 
seeds  or  buds." 

Each  bud,  therefore,  has  a  kind  of  individuality  of  its  own. 
All  but  the  first  are  developed  asexually,  yet  all  shades  of  differ- 
ences will  be  found  among  these  different  members  of  what  we 
call  a  plant  or  tree ;  hence  each  branch  or  phyton  is  a  bud 
variety,  and  one  which  can  be  propagated  by  cuttings  or  by  seeds 
or  by  both,  and  in  either  case  can  doubtless  be  improved  by 
selection.3 

Bailey  makes  the  statement4  that  "  the  seeds  of  bud  varieties 
are  quite  as  likely  to  reproduce  the  variety  as  the  seeds  of  seed 
varieties  are  to  reproduce  their  parents."  5  He  quotes  Darwin 
in  saying  that  "  moss  roses  (which  are  bud  varieties)  generally 
reproduce  themselves  by  seed,  and  the  mossy  character  has  been 
transferred  by  crossing  from  one  species  to  another."  If  this 
be  true,  —  if  bud  variations  are  transmitted  by  the  seed,  even 
to  the  slightest  degree,  —  then  the  changes  wrought  in  bud  vari- 
ation must  be  profound,  extending  as  they  do  to  the  constitution 
of  the  germ,  a  fact  which  argues  much  for  the  ever-present 

1  Bailey,  Survival  of  the  Unlike,  pp.  80-106. 

2  Ibid.  p.  105. 

3  Ibid.  pp.  90-92. 

4  Ibid.  p.  94. 

6  Professor  Bailey  does  not  intend  to  say  that  seeds  of  bud  varieties  are  certain 
to  come  true,  but  rather  that  no  seed  exactly  reproduces  the  parent  plant. 


CAUSES  OF  VARIATION 

liability  to  internal  change  and  not  at  all,  as  is  erroneously  sup- 
posed, for  the  inheritance  of  acquired  characters,  because  the 
characters  in  question  were  not  "acquired"  in  the  ordinary 
acceptance  of  the  term,  —  they  were  the  result  of  internal,  not 
external,  impulses. 

SECTION  V  — INFLUENCE   OF   THE  CONDITION  OF  THE 
GERM  UPON   DEVELOPMENT 

Staleness.  Both  the  male  and  the  female  germ  cells  are 
capable  of  living  for  a  considerable  time  after  maturation,  so 
that  fertilization  may  be  somewhat  delayed  ;  how  long  is  not 
known,  and  what  the  effect  of  delay  may  be  is  not  fully 
understood. 

Experiments  by  Vernon  upon  the  ova  and  spermatozoa  of  the 
sea  urchin  of  different  ages,  from  nine  to  forty-five  hours,  indicate 
that  the  size  of  the  larva  is  in  some  degree  dependent  upon  the 
freshness  of  the  germ  at  fertilization.1  The  results  of  a  number 
of  trials  were  as  follows  : 

1 .  With  stale  ova  and  stale  sperm  the  resulting  larvae  differed 
but  slightly  from  the  normal  (in  which  both  were  fresh). 

2.  With  fresh  ova  and  stale  sperm  the  larvae  were  distinctly 
larger  (5.8  per  cent). 

3.  With  stale  ova  and  fresh  sperm  the  larvae  were  distinctly 
smaller  than  when  both  were  fresh  (4.9  per  cent). 

It  is  certain  that  the  above  combinations  as  to  staleness  are 
possible  in  the  fertilization  of  mammals  by  mating  and  of  plants 
by  pollination.  Whether  the  results  are  the  same  and  whether 
the  differences  persist  through  life  are,  of  course,  unknown.  The 
facts  recorded  are  suggestive,  but  whether  they  will  ever  be 
useful  remains  to  be  determined. 

Individuality  of  the  germ.  That  successive  germ  cells  from 
the  same  individual  may  be  substantially  different,  even  aside 
from  considerations  of  maturation,  is  a  fact  beyond  question. 
The  ear  of  corn,  like  its  tassel,  matures  from  the  base  upward. 
The  tip  kernels  are  not  only  younger  but  decidedly  smaller  than 
their  half-sisters  at  the  base.  The  different  peas  in  a  pod  are 

1  Vernon,  Variation  in  Animals  and  Plants,  pp.  105-108. 


INTERNAL  CAUSES  OF  VARIATION  183 

not  equally  developed.  One  of  the  twin  pair  of  oats  is  more  or 
less  undeveloped.  Is  this  difference  in  size  due  to  season,  food 
supply,  room,  or  to  some  peculiarity  in  the  germ  ?  It  may  be  lack 
of  room  in  pod-bearing  plants,  but  it  cannot  be  that  in  the  case 
of  corn.  The  strong  presumption  is,  in  the  opinion  of  the  writer, 
that  these  differences  in  size  are  partly  due  to  differences  in  food 
supply  but  more  largely  to  inherent  differences  in  the  germs. 

SECTION  VI— XENIA,  OR  FERTILIZATION  OF  THE 
ENDOSPERM,  — DOUBLE  FERTILIZATION 

If  one  kind  of  corn  be  fertilized  by  another,  the  mixture  will 
show  the  first  year.  For  example,  if  white  and  yellow  corn  be 
planted  side  by  side,  the  white  ears  will  have  many  yellow  grains, 
showing  at  once  the  effects  of  cross  fertilization.  These  "  off" 
kernels  are  the  mixed  seeds,  but,  reasoning  from  analogy,  we 
should  not  expect  the  mixture  to  appear  until  the  grains  are 
planted  and  the  generation  of  mixed  breeding  is  at  hand.  The 
visible  part  of  the  kernel  is  not  the  germ ;  it  is  the  "  endo- 
sperm," or  surrounding  portion,  which  serves  as  food  for  the 
sprout  until  the  young  plant  has  established  itself.  It  is  related 
to  the  germ  much  as  the  white  of  egg  and  its  shell  are  related 
to  the  yolk.  Fertilization  is  of  the  germ.  How,  then,  do  these 
outside  parts  become  affected  ? 

It  will  be  remembered  that  in  the  animal  the  female  germ 
gives  rise  to  one  mature  functional  cell,  the  ovum,  and  three 
non-functional,  the  polar  bodies ;  that  the  male  cell  gives  rise 
also  to  four  mature  cells,  the  spermatozoa,  all  functional,  and 
that  the  nucleus  of  the  one  unites  directly  with  that  of  the 
other  without  intervening  nuclear  divisions. 

In  plants,  however,  it  is  found  to  be  substantially  different. 
The  mature  female  cell,  corresponding  to  the  ovum,  instead  of 
awaiting  fertilization,  continues  its  activity,  undergoing  gener- 
ally two  (sometimes  more)  divisions  of  the  nucleus,  giving  rise 
to  eight,  or  some  other  corresponding  number  of  "  sub-nuclei," 
which  remain  floating  within  the  cytoplasm.  It  will  be  remem- 
bered that  of  these  eight  sub-nuclei  only  one  is  capable  of  func- 
tioning as  an  egg  nucleus  ;  also  that  two  others  remain  near 


1 84  CAUSES  OF  VARIATION 

the  center  of  the  embryo  sac  to  form  the  endosperm.  It  will 
be  remembered,  also,  that  the  pollen  nucleus  undergoes  a  second 
division  during  its  progress  down  the  pollen  tube  and  before 
uniting  with  the  egg  nucleus. 

Of  this  divided  nucleus  one  portion  unites  with  the  single 
functional  member  of  the  female  group,  making  the  germ,  and 
in  cases  such  as  are  now  under  consideration  the  other  joins 
with  the  minor  members  concerned  with  the  development  of 
the  endosperm.  In  this  way,  by  means  of  this  kind  of  double 
fertilization,  the  endosperm  is  itself  affected  and  the  crossing  is 
evident  the  first  year. 

Of  course  this  visible  effect  upon  the  endosperm  is  of  itself 
purely  transitory,  having  no  influence  upon  the  line  of  descent. 
The  real  effect  of  pollination  is  manifestly,  as  in  all  other  ferti- 
lization, confined  to  the  germ. 

Whether  the  two  fertilizations  are  similar  as  to  comparative 
influence  of  the  two  parents  no  one  knows,  nor  does  it  greatly 
matter.  The  effect  upon  the  endosperm  enables  us  to  detect 
the  cross,  if  it  is  capable  of  detection,  and  to  remove  the  con- 
taminated seeds  if  we  desire  to  retain  purity.  If  the  object  be 
to  secure  crossing,  we  shall  of  course  subsequently  deal  with 
the  products  of  the  cross-bred  germ,  which  only  are  significant 
from  the  breeder's  standpoint. 

Just  what  species  indulge  in  this  double  fertilization  is  not 
well  known.  It  is,  however,  well  established  in  a  large  number, 
and  the  process  is  supposed  to  be  common  rather  than  unusual. 

Effect  of  crossing  upon  fruit  in  general.  What  the  layman  calls 
fruit  is  commonly  not  the  endosperm  that  has  been  under  dis- 
cussion but  the  thickened  and  much  developed  fleshy  receptacle 
on  which  the  seeds  are  borne.  It  has  been  claimed  that  these 
parts  are  directly  influenced  the  first  year  by  crossing,  so  that  the 
character  of  strawberries,  apples,  pears,  melons,  squashes,  etc., 
depends  much  upon  the  source  of  the  pollen  used  in  fertilization. 

This  claim  has  never  been  well  substantiated  by  direct  experi- 
ment. Dr.  Burrill,  of  the  University  of  Illinois,  tells  me  that  he 
crossed  Crescent  strawberries  both  with  the  Sharpless  and  with 
a  wild  berry  especially  selected  for  its  insignificant,  worthless 
fruit.  Nobody  was  able  to  detect  the  difference  in  the  resulting 


INTERNAL  CAUSES  OF  VARIATION  185 

crops.  So  far  as  is  known  to  the  writer,  the  same  principle  holds 
in  other  fruits.  It  is  the  endosperm  and  not  the  receptacle  that 
is  directly  affected  by  fertilization,  and  any  influence  upon  the 
latter  must  be  indirect  and  comparatively  slight. 

Possible  indirect  effect  of  pollination  upon  the  development  of 
fruit.  Though  the  receptacle  is  not  itself  fertilized,  its  develop- 
ment is  conditioned  upon  that  of  its  superincumbent  seeds, 
which  are  themselves  directly  dependent  upon  fertilization  for 
their  development. 

This  fleshy  growth  of  the  receptacle  is,  therefore,  the  result 
of  a  kind  of  stimulus  from  the  growing  germ,  and  it  is  con- 
ceivable that  this  stimulus  may  differ  somewhat  in  degree, 
depending  upon  the  source  of  the  pollen.  In  this  way  the  size 
of  the  fruit  might  be  indirectly  influenced  by  the  pollen ;  and 
in  fruits  like  the  pear,  which  are  not  concentric  about  the  seeds, 
even  the  shape  might  be  influenced  in  the  manner  noted. 

All  this  is  quite  independent  of  certain  markings  of  fruit 
which  may  arise  by  those  dispositions  of  color  which  are  every- 
where responsible  for  stripes  and  spots,  and  whose  causes  are 
not  as  yet  understood. 

SECTION   VII— TELEGONY 

The  term  "  telegony  "  is  synonymous  with  "  infection  of  the 
germ"  and  the  ''influence  of  previous  impregnation." 

By  this  is  meant  the  supposed  influence  of  the  male  upon  the 
female  in  such  a  way  as  to  affect  future  offspring  by  other  sires. 

Breeders  of  animals  quite  generally  believe  that  the  influence 
of  one  impregnation,  especially  the  first,  is  permanent  and  will 
affect  all  future  offspring ;  indeed,  some  go  so  far  as  to  say 
that  a  female  once  mated  to  a  male  of  a  different  breed  is  ever 
afterwards,  for  breeding  purposes,  herself  a  cross-bred  animal)- 

This  supposedly  permanent  effect  of  the  male  upon  the  female 
has  been  especially  claimed  for  horses,  dogs,  and  men. 

Telegony  in  horses.  The  classic  example  among  horses,  and 
the  one  that  is  everywhere  cited  as  proof  of  the  theory,  is  the 

1  This  theory  seems  to  be  limited  to  animals.  The  writer  is  not  aware  that  it 
has  ever  been  claimed  for  plants. 


!86  CAUSES  OF  VARIATION 

instance  of  Lord  Morton's  mare  mentioned  by  Darwin.1  This 
mare  bore  a  colt  by  a  quagga,  which  was  of  course  striped  after 
the  manner  of  his  sire.  She  afterwards  bore  two  colts  by  a 
stallion,  both  of  which  were  said  to  have  been  marked  with 
bars  on  shoulders  and  legs  supposedly  showing  the  effects  of 
the  quagga  upon  the  offspring  of  the  stallion. 

Professor  Ewart,  of  Edinburgh,  has  recently  repeated  this 
experiment  on  an  extended  scale,  with  results  showing  no  trace 
of  the  quagga  beyond  his  own  offspring.2  Recent  investigations 
in  contemporary  literature  throw  grave  doubt  upon  the  essential 
accuracy  of  the  data  at  Darwin's  hand.  They  seem  to  show 
that  the  supposed  resemblance  of  the  stallion  colts  to  the  quagga 
was  exceedingly  fanciful,  probably  being  nothing  beyond  what 
appears  frequently  in  young  horses  of  the  purest  parentage, 
dun-colored  horses  as  a  rule  showing  more  or  less  tendency  to 
stripes  and  bars. 

It  is  one  of  the  best  evidences  of  the  power  of  tradition  that 
this  single  instance,  happening  more  than  a  hundred  years  ago, 
has  done  duty  ever  since  to  prove  (?)  an  exceedingly  doubtful 
theory  and  an  almost  unaccountable  belief.  It  is  remarkable 
that  so  uncertain  a  circumstance,  and  one  so  easy  of  repetition, 
with  universal  experience  tending  constantly  to  throw  light  upon 
the  subject,  should  have  been  so  excessively  overworked.  It 
shows,  as  no  other  instance  has  ever  shown,  the  persistence  of 
tradition,  the  extent  of  credulity  in  the  presence  of  the  phenom- 
enal, and  the  willingness  of  men  to  repeat  an  assertion,  or  even 
an  opinion,  until  by  mere  repetition  it  comes  to  have  all  the 
force  of  authority.  The  thanks  of  the  world  are  due  to  Professor 
Ewart  for  his  excellent  work  in  disposing,  by  direct  experiment, 
of  a  citation  that  has  done  damage  long  enough.  It  is  to  be 
hoped  that  the  question  may  at  least  be  held  open  until  some 
sort  of  positive  evidence  is  brought  forward  that  is  worthy  the 
credence  of  careful  students. 

Telegony  in  dogs.  Dog  fanciers  are  pretty  generally  credited 
with  believing  in  telegony,  especially  in  case  of  first  matings. 

1  See  Darwin,  Animals  and  Plants  under  Domestication,  chap,  xiii,  p.  17,  of 
second  edition  by  Appleton.  (Quoted  from  Philosophical  Transactions,  1821, 
P-  25).  2  Rreejerj  Gazette,  XI,T,  1009. 


INTERNAL  CAUSES  OF  VARIATION  187 

The  best  students,  however,  insist  that  very  little  real  evidence 
has  been  produced  on  the  subject,  and  none  at  all  tending  to 
prove  the  existence  of  this  influence.1 

With  a  view  to  testing  somewhat  the  real  extent  of  this  be- 
lief, the  author  addressed  letters  to  the  best-known  dog  fan- 
ciers of  the  United  States.  Of  thirty-seven  answers  received, 
one  writer  is  a  believer  in  telegony ;  six  somewhat  mildly 
express  uncertainty ;  two  are  non-committal ;  and  twenty-eight 
are  outspoken  against  the  theory.  The  most  outspoken  of  them 
all  is  a  well-known  fancier  of  long  experience.  Judging  from 
this  small  number,  it  would  seem  that  this  belief  among  dog 
fanciers  has  been  overrated. 

Proof  by  the  method  of  instance.  Without  a  reasonable  doubt 
belief  in  telegenic  influence  rests  upon  stray  instances,  difficult 
of  understanding  by  those  who  happened  to  be  the  observers, 
and  hastily  accepted  as  evidence.  Now  nobody  should  be  more 
careful  than  the  breeder  to  judge  accurately  the  nature  and 
value  of  evidence.  A  single  instance  may  be  good  negative 
testimony,  but  it  is  seldom  worth  much  as  positive  evidence. 
The  products  of  breeding  are  so  many  and  so  various,  and  the 
causes  of  variation  are  so  numerous  and  so  complicated,  that  a 
particular  result  can  seldom  be  assigned  to  the  operation  of  any 
single  cause.  It  is  more  likely  the  mixed  or  composite  result 
of  many  influences,  both  internal  and  external ;  and  in  order  to 
know  the  effect  of  a  single  cause  it  is  necessary  to  isolate  the 
case  if  possible,  or,  if  not,  to  resort  to  the  examination  of  large 
numbers  of  cases,  subject  to  varying  degrees  of  influence,  and 
thus  indirectly  to  estimate  the  effect  of  any  special  cause  of  vari- 
ation. For  example,  stripes  and  bars  were  once  common  color 
markings  of  horses,  as  they  are  now  of  asses,  especially  zebras 
and  quaggas.  Consequently  a  certain  proportion  of  colts,  what- 
ever the  parentage,  will  be  born  with  traces  of  shoulder  and  leg 
markings.  Now,  under  the  laws  of  chance,  a  certain  portion  of 
these  will  be  the  direct  offspring  of  striped  or  barred  sires,  and 
will  attract  no  attention,  the  markings  being  considered  heredi- 
tary. By  the  same  law  of  chance  a  certain  (smaller)  portion  will 
be  the  offspring  of  parents  not  barred,  and  a  still  smaller  number 

1  Proceedings  of  the  Royal  Society,  LX,  273. 


!88  CAUSES  OF   VARIATION 

will  be  the  progeny  of  unbarred  sires  and  out  of  dams  once  mated 
with  barred  sires  for  other  offspring.  This  smallest  portion,  get- 
ting its  bars  not  by  direct  descent  but  by  reversion^  will  most 
likely  be  erroneously  considered  to  have  derived  them  from  the 
barred  male  not  their  sire.  The  same  is  true  of  other  markings, 
and  on  such  evidence  as  this  the  theory  of  telegony  has  been 
built  up,  and,  so  far  as  proof  goes,  it  rests  on  no  better  founda- 
tion as  yet.  In  order  to  secure  evidence  amounting  to  proof,  it 
is  necessary  to  examine  large  numbers  involving  both  positive  and 
negative  evidence,  in  order  to  secure  trustworthy  averages.  When- 
ever this  has  been  done  the  theory  of  telegony  fails  of  support. 

Telegony  in  man.  The  statistical  method  has  been  applied  by 
Pearson1  in  the  case  of  man.  He,  together  with  Galton,  pos- 
sesses data  covering  hundreds  of  individuals  in  English  families. 
He  reasoned  that  if  the  sire  exerts  a  permanent  influence  upon 
the  dam,  tending  to  assert  itself  in  all  future  offspring,  then  this 
influence  must  be  in  a  sense  cumulative,  so  that  the  younger  sons 
in  the  family  will  tend  to  resemble  the  father  slightly  more  than 
will  the  older  sons,  conceived  before  such  influences  have  become 
established. 

His  study  covered  385  brother  brothers  and  450  sister  sisters, 
taken  two  and  two.  In  some  instances  there  was  considerable 
difference  in  ages,  and  in  others  they  were  successive  children. 
His  data  covered  both  height  and  arm  length,  and  after  making 
the  usual  allowances  for  sex  and  age  Pearson  concludes  that,  so 
far  as  these  characters  are  concerned,  "no  steady  telegonic 
influence  exists." 

Again,  the  many  successive  marriages  of  both  colored  and 
white  women  to  men  of  opposite  color  should  afford  numerous 
examples  of  telegony  were  it  a  consequential  force  in  heredity. 

Scientific  objections  to  the  theory  of  telegony.  If  telegony 
exists,  its  influence  over  hereditary  characters  must  be  explained, 
so  far  as  present  knowledge  goes,  in  one  of  three  ways  :  ( i )  some 
effect  upon  the  tissues  of  the  female  such  as  will  influence 
future  ova  in  their  maturation  or  the  embyro  in  its  development ; 
(2)  something  like  a  partial  fertilization  of  immature  and  unde- 
veloped ova,  in  such  a  way  as  to  influence  their  character  at 

1  Proceedings  of  the  Royal  Society,  LX,  273. 


INTERNAL  CAUSES   OF   VARIATION  189 

maturation ;  (3)  the  retention  of  the  spermatozoa  from  the 
first  mating,  and  their  action  in  successive  fertilizations. 

As  to  the  first,  there  is  no  scientific  ground  for  assuming  the 
slightest  effect  of  the  spermatozoa  upon  the  tissues  of  the 
female.  It  is  the  ovum  that  is  fertilized,  not  the  female,  as  was 
at  one  time  supposed  when  fertilization  was  regarded  solely  as 
a  stimulus. 

As  to  the  second,  there  is  no  ground  for  believing  that  the 
nuclei  of  growing  immature  oogonia  are  in  condition  to  unite,  or 
that  they  are  capable  of  uniting,  with  the  nuclei  of  other  cells  in 
any  capacity  whatever. 

As  to  the  third,  there  is  every  ground  for  believing  that  the 
spermatozoa  are  not  retained  for  any  considerable  time,  else 
successive  births  would  occur  from  a  single  mating.  Moreover, 
as  but  one  spermatozoon  takes  part  in  fertilization,  the  blended 
effect  of  two  sires  is  impossible.  It  is  even  impossible  in  multiple 
births  when  two  services  are  close  together.  If  a  litter  of  pigs 
is  the  result  of  two  matings  by  different  sires,  some  may  resemble 
one  sire  and  some  the  other,  but  none  will  resemble  both. 

SECTION  VIII  —  INTRA-UTERINE  INFLUENCES 

It  is  a  widespread  tradition  that  distinct  characters,  especially 
abnormalities,  may  be  impressed  upon  the  individual  while  in  utero 
through  the  imagination  or  other  strong  mental  impression  of  the 
mother.  It  has  even  been  held  in  the  case  of  hens,  which  would 
necessitate  the  exertion  of  the  influence  upon  the  ovum  itself. 

The  usual  argument  is  that  the  intimate  contact  between 
the  mother  and  the  fetus  renders  the  latter  peculiarly  susceptible 
to  influences  affecting  the  former.  Thus  marks  and  deformities 
of  all  sorts  are  popularly  attributed  to  unfortunate  sights  and 
experiences  of  the  mother  before  the  birth  of  the  young.  Pecul- 
iarly marked  calves  are  said  to  owe  their  markings  to  the  strong 
mental  impressions  created  by  a  steer  or  by  other  cows,  and  colts 
are  believed  by  many  to  owe  their  color  not  so  much  to  the  sire 
as  to  the  gelding  mate  that  worked  beside  the  dam  while  she  was 
carrying  her  young.  Persons  with  whom  the  tradition  is  strong- 
often  display  a  blanket  of  a  pleasing  color  before  the  eyes  of  the 


190 


CAUSES  OF  VARIATION 


mare  at  the  time  of  service,  and  of  course  are  extremely  care- 
ful to  protect  her  from  unpleasant  colors  of  any  sort.1  The 
hold  of  this  theory  upon  the  popular  mind  is  the  best  example 
afforded  by  breeding  of  the  strength  of  tradition.  The  supposed 
reason  on  which  it  rests  has  slight  basis  in  fact.  The  contact 
between  the  mother  and  the  fetus  is  not  so  intimate  as  is  popu- 
larly supposed.  The  fetus  is  absolutely  dependent  upon  the 
mother  for  nourishment,  it  is  true,  and  it  lies  floating  in  its 
fleshy  incasement,  which  is  in  intimate  contact  with  the  tissues 
of  the  uterus ;  but  there  is  no  organic  connection,  no  nervous 
interrelation  whatever. 

Anything  which  would  curtail  or  shut  off  nourishment  would 
of  course  injure  or  destroy  the  fetus.  It  is  also  subject  to  other 
accidents,  as  becoming  entangled  in  its  own  cord,  which  may 
thus  divide  a  limb  or  cause  strangulation,  —  all  of  which,  how- 
ever, is  quite  aside  from  the  matter  in  point. 

The  real  question  is  whether,  and  to  what  extent,  the  fetus  is 
influenced  by  peculiarities  of  nourishment  during  its  develop- 
ment. It  would  of  course  be  injured  by  poisons,  and  the  danger 
from  administering  anaesthetics  is  great,  but  this  discussion  is 
limited  to  the  direct  effect  of  mental  impressions. 

The  indifference  of  the  fetus  to  its  source  of  nourishment  is 
shown  by  an  experiment  of  Heape,2  performed  for  another  pur- 
pose, but  throwing  light  upon  these  questions.  In  this  experiment 
"  two  segmenting  ova  were  obtained  from  an  Angora  doe  rabbit 
which  had  been  fertilized  by  an  Angora  buck  thirty-two  hours 
previously,  and  were  immediately  transferred  to  the  upper  end 
of  the  Fallopian  tube  of  a  Belgian  hare  rabbit  which  had  been 
fertilized  three  hours  before  by  a  buck  of  the  same  breed  as 
herself.  In  due  course  this  Belgian  hare  doe  gave  birth  to  six 
young.  Four  of  these  resembled  herself  and  her  mate,  but  the 
other  two  were  undoubted  Angoras.3  .  .  .  Both  of  the  Angoras 
were  born  bigger  and  stronger  than  any  of  the  other  young,  and 

1  For   a   good   collection    of   alleged    instances,  see    Miles,   Stock   Breeding, 
pp.  281-295,  or  consult  any  neighborhood  oracle. 

2  Vernon,  Variation  in  Animals  and  Plants,  pp.  119-120;   also  Proceedings  of 
the  Royal  Society,  XLVIII,  457. 

8  The  Angoras  were  characterized  and  easily  distinguished  by  their  long, 
silky  hair  and  their  habit  of  swaying  the  head  from  side  to  side. 


INTERNAL  CAUSES  OF  VARIATION 

they  all  along  maintained  their  supremacy  in  this  direction." 
Whatever  this  experiment  proves  or  does  not  prove,  it  shows 
conclusively  that  a  fertilized  Angora  germ  preserves  and  develops 
its  inherent  characters  perfectly  in  an  exceedingly  foreign  envi- 
ronment, on  which  it  evidently  depends  only  for  nourishment. 

Mental  impressions  and  nervous  conditions  are  commonly  in- 
voked to  explain  birth  marks  and  other  natural  abnormalities,  such 
as  the  loss  of  a  finger.  In  this  connection  two  facts  are  to  be 
carefully  considered  :  first,  there  is  certain  to  occur  a  large  num- 
ber of  marks  ("  strawberry,"  "  cucumber,"  and  others)  and  many 
malformations  of  one  kind  or  another.  Scarcely  an  individual  is 
absolutely  free  from  something  of  the  kind.  Again,  mothers  are 
subjected  to  all  sorts  of  sights,  sounds,  and  experiences  during  the 
many  weeks  of  embryonic  development,  and  it  would  be  strange 
indeed  if  out  of  the  thousands  of  cases  some  correspondence 
between  marks  and  experience  could  not  be  figured  out,  espe- 
cially by  one  whose  belief  is  fixed  and  who,  having  the  case  at 
hand,  needs  only  to  find  the  proper  "  corresponding  experience." 
The  law  of  chance  alone  will  insure  an  occasional  correspondence 
between  the  two,  —  entirely  enough  to  start  the  tradition  and 
to  maintain  it  afterward.  As  in  theories  concerning  the  control 
of  sex,  any  theory  stated  will  be  verified  half  the  time  because 
there  is  but  one  alternative,  so  here,  while  the  alternatives  are 
more,  the  correspondence  is  certain  sometimes  to  appear  under 
the  law  of  chance  alone. 

Another  fact  to  be  reckoned  with  is  that  if  the  fetus  were  so 
sensitive  to  mental  impressions  as  to  require  the  display  of 
properly  colored  blankets,  —  if  females  were  so  susceptible  as 
this  to  surrounding  sights,  — what  a  jumble  of  colors  our  domes- 
tic animals  would  speedily  display.  In  the  opinion  of  the  writer 
this  tradition  has  neither  a  scientific  basis  nor  well-established 
instances,  and  it  is  time  it  no  longer  occupied  the  minds  of 
breeders  to  the  exclusion  of  far  more  important  matters.  In  this 
connection  it  is  worthy  of  remark  that  if  the  average  breeder 
were  half  as  familiar  with  important  facts,  and  half  as  attentive 
to  their  bearing  upon  his  operations,  as  he  is  familiar  with  and 
attentive  to  floating  traditions,  we  should  have  a  far  smaller 
proportion  of  worthless  animals. 


1 92  CAUSES  OF  VARIATION 

SECTION  IX  — REVERSION  AND  ATAVISM 

These  two  terms  are  used  to  designate  characters  appearing 
in  the  offspring  but  not  visible  in  the  parents.  "  Reversion  "  is 
used  to  indicate  resemblance  to  a  comparatively  near-by  ancestor, 
not  the  parent,  while  "  atavism  "  refers  to  exceedingly  remote 
ancestors,  sometimes  of  other  and  foundation  species. 

Thus,  if  a  dash  of  impurity  of  blood  enters  a  herd,  it  will 
appear  occasionally  for  many  generations.  This  would  be 
spoken  of  as  a  "  reversion  to  the  strange  blood."  If  a  sire  or 
dam  has  some  peculiar  character,  like  white  stockings  in  horses, 
a  peculiar  horn  in  cattle,  or  a  habit  in  man,  it  is  likely  to  appear 
from  time  to  time  in  future  generations,  even  after  its  real 
origin  is  forgotten.  This  is  a  reversion.  English  breeds  of  cattle 
are  developed  from  the  ancient  wild  white  cattle  of  Britain,  and 
the  occasional  appearance  in  all  these  breeds  of  a  white  calf 
with  red  or  brown  ears,  lower  legs,  and  tail  brush  is  to  be 
expected.  It  is  a  reversion,  not  a  proof  of  mixed  blood.  Of 
course  the  animal  so  marked  is  useless  for  breeding  purposes, 
but  no  reproach  to  the  herd,  and  none  necessarily  to  the  dam  that 
produced  it,  for  reversions  for  the  most  part  seem  to  come  singly. 

Atavism,  on  the  other  hand,  goes  farther  back.  For  example, 
mammals  during  their  early  embryonic  development  still  show 
traces  of  the  gill  slits,  thus  betraying  their  undoubted  one-time 
connection  with  the  same  stock  which  gave  rise  to  the  aquatic 
animals.  These  gill  slits  occasionally  persist,  failing  to  close, 
and  give  rise  to  the  abnormality  known  as  "  cervical  fistula."  It 
is  an  undoubted  atavistic  abnormality,  —  an  extreme  case  of 
course,  because  of  its  antiquity. 

Cases  of  this  kind  are  to  be  carefully  distinguished  from  mere 
meristic  variations.  For  example,  the  sudden  appearance  of  a 
three-toed  horse  would  be  regarded  as  atavistic,  for  all  horses 
once  had  three  toes ;  but  a  sixth  digit  in  man  is  certainly  not 
atavistic,  for  we  have  no  evidence  that  man  ever-  possessed 
normally  more  than  five  digits.  The  criminal  instinct  in  certain 
men  is  undoubtedly  atavistic,  showing  not  so  much  a  delight 
in  evil  doing  as  an  entire  absence  of  the  higher  sense  of  right 
doing. 


INTERNAL   CAUSES  OF  VARIATION  193 

There  are  certain  intermediate  cases  difficult  to  name.  An 
occasional  cow  gives  no  more  milk  than  her  wild  progenitor  ;  a 
hog  resembles  not  his  immediate  kind,  but  his  striped  and  long- 
nosed  ancestor,  the  wild  boar  of  the  bush  ;  the  horse  or  the 
sheep  paws  snow  the  first  time  he  sees  it,  though  cattle  do  not ; 
the  dog  turns  many  times  around  in  lying  down,  as  if  making  his 
nest ;  the  occasional  horse  has  bars  on  his  legs  and  stripes  on 
his  shoulders.  Which  term  shall  be  applied  ? 

These  are  undoubtedly  line  cases,  and  all  would  not  agree  as 
to  whether  they  should  be  regarded  as  reversions  or  instances  of 
atavism.  Because  of  our  very  frequent  need  for  a  term  to  cover 
experiences  met  almost  every  day  by  the  breeder,  and  due  to 
more  near-by  causes,  the  writer  is  of  the  opinion  that  it  is  better 
for  our  purposes  to  extend  the  meaning  of  the  word  "  atavism  " 
well  forward,  making  it  cover  cases  of  remote  characters,  even 
within  the  species  (like  those  just  given),  leaving  the  term 
"  reversion,"  which  will  be  much  more  frequently  needed,  to  cover 
the  more  near-by  cases  that  occur  every  day  in  our  herds,  and 
that  would  be  traceable,  could  we  know  all  the  facts,  to  an  old 
but  not  remote  ancestor. 

Inheritance  is  from  the  race.  It  is  evident  that  inheritance  is 
not  limited  to  the  visible  characters  of  the  immediate  parent. 
We  constantly  forget  that  every  individual  is  possessed  of  and 
capable  of  transmitting  all  the  characters  of  the  race  to  which 
he 'belongs.  We  forget  that  his  visible  characters  are  not  his 
total  possession,  but  only  those  which  are  relatively  most  prom- 
inent in  his  case.  Other  combinations  are  easily  possible  out  of 
the  same  elements  in  slightly  different  proportions,  and  it  is  not 
so  strange  as  we  think  that  a  character  once  in  possession  of  a 
race  tends  to  persist  indefinitely  and,  perforce,  occasionally  to 
become  visibly  apparent.  It  is  as  bound  to  appear,  under  the 
law  of  chance,  as  is  the  one  black  ball  in  the  box  of  a  thousand 
or  a  million,  if  only  throws  enough  are  made. 

The  work  of  Galton,  while  mostly  confined  to  man,  yet  shows 
clearly  that  inheritance  is  not  in  strict  line  with  the  visible 
parental  characters,  but  is  in  large  measure  independent  of  the 
immediate  parents.1 

1  See  the  Regression  Table,  sect,  iii,  chap.  xiv. 


194 


CAUSES  OF  VARIATION 


Galton  has  endeavored  to  assess  mathematically  the  fraction 
of  direct  inheritance,  or,  more  accurately,  the  similarity  between 
the  child  and  its  various  ancestors.  From  his  studies  he  con- 
cludes that  the  visible  or  dominant  characters  of  the  child  are, 
on  the  average,  inherited  (that  is,  correspond  with  those  of  the 
various  ancestors),  roughly,  as  follows  1 : 

From  the  immediate  parents 50  per  cent 

From  the  grandparents      .......  25  per  cent 

From  the  great-grandparents 12.5  per  cent 

From  the  great,  great-grandparents     .     .     .  6.25  per  cent 
Earlier  ancestors  in  proportion 

Pearson,  working  with  larger  numbers  and  diverse  characters, 
concludes  that  Galton's  fraction  of  direct  inheritance  (0.50)  is 
too  high,  and  is  inclined  to  believe  it  not  above  0.40  for  blended 
characters.  The  subject  will  be  pursued  farther  under  "  The 
Law  of  Ancestral  Heredity,"  but  this  glimpse  into  the  nature  of 
inheritance  is  the  best  method  known  to  the  author  to  dissolve 
the  almost  supernatural  mystery  that  has  been  thrown  around 
reversion  and  its  natural  corollary,  latent  characters.  The  study 
can  be  pursued  no  farther  at  this  point,  but  what  has  been  said 
will  serve  to  show  that  reversion  (regression)  is  a  fertile  cause 
of  variation  as  calculated  from  the  type  of  the  parent.  It  will 
serve  also  as  an  introduction,  preparing  the  student  for  the  more 
serious  study  of  inheritance  later  on,  when  we  shall  learn  that 
the  real  type,  from  which  all  departures  should  be  reckoned,  is 
the  type  of  the  race,  and  not  the  special  type  of  the  parent,  or 
even  of  the  mid-parent. 

SECTION  X  — INDIVIDUAL  CHARACTERS  DEPENDENT 

UPON  SEX 

That  both  sexes  possess  and  transmit  all  the  characters  of  the 
race  is  a  well-established  fact  in  evolution.  It  is  also  true  that 
the  particular  characters  to  undergo  development,. and  the  extent 

1  Vernon,  Variation  in  Animals  and  Plants,  p.  123;  Proceedings  of  the  Royal 
Society,  LXI,  401,  1897;  Galton,  Natural  Inheritance,  p.  191.  This  does  not 
mean  that  every  individual  will  inherit  in  this  proportion,  but  that  the  fractions 
express  averages. 


INTERNAL   CAUSES  OF   VARIATION  195 

to  which  they  will  develop  depends  very  much  upon  the  sex  of 
the  individual.  How  much  allowance  to  make  on  account  of  sex 
in  comparing  one  individual  with  another  of  a  different  sex  we 
are  in  most  cases  unable  to  say,  —  not  from  the  impossibility  of 
knowing,  but  from  the  fact  that  in  respect  to  most  characters 
the  matter  has  not  yet  been  worked  out.  It  is  easily  possible, 
however. 

For  example,  in  respect  to  stature,  men  are  8  per  cent  taller 
than  women,  so  that  when  the  heights  of  the  latter  are  multi- 
plied by  i.oS1  the  two  are  strictly  comparable,  and  not  before. 
When  this  is  done  the  difference  due  to  sex  has  been  eliminated, 
and  the  statures  of  men  and  women  may  be  directly  compared. 

In  general,  males  and  females  exhibit  the  same  characters, 
but  in  varying  degrees.  For  example,  the  woman  as  well  as  the 
man  has  hair  on  the  face,  but  in  less  amount  ;  the  male  as  well 
as  the  female  has  nipples,  but  they  are  rudimentary.  Among 
mammals  and  the  domestic  animals  generally  the  male  is  heavier 
in  front,  generally  of  a  more  robust  build,  and  considerably 
larger  than  the  female,  —  a  distinction  that  by  no  means  holds 
in  animal  life  generally. 

In  the  present  state  of  knowledge  we  simply  know  that  the 
general  appearance  of  the  individual  and  its  character  devel- 
opment are  largely  dependent  upon  its  sex ;  but  to  what  exact 
extent  remains  in  most  cases  to  be  determined,  and  the  deter- 
mination must  be  made  before  we  can  compare  individuals  of 
different  sexes  with  any  degree  of  accuracy.  Without  a  doubt 
distinctions  in  sex  have  been  greatly  overworked,  the  differ- 
ences being  mostly  of  degree  rather  than  of  kind,2  and  far  less 
consequential  than  has  been  supposed. 

Individuals  deprived  of  their  sexual  organs  by  castration  or 
by  spaying  do  not  develop  their  primary  sexual  characters.  The 
castrated  male  is  not  a  female,  as  is  sometimes  erroneously 
believed,  but  a  male  arrested  in  his  development ;  and  the  spayed 
female  is  an  undeveloped  female.  As  would  be  expected,  both 

1  These  data  are  the  result  of  Galton's  study  of  the  stature  of  English  people. 
See  Galton,  Natural  Inheritance. 

2  It  is  idle  to  attempt  to  prove  that  certain  characters,  aside  from  those  of 
reproduction,  are  especially  identified  with  one  sex. 


196  CAUSES  OF   VARIATION 

take  on  the  secondary  sexual  characters  (those  dominant  in  the 
other  sex)  prematurely  young.1 

Many  entire  individuals  never  develop  strongly  the  primary 
characters  of  their  own  sex.  There  are  effeminate  males  and 
masculine  females, —  those  in  which  the  characters  of  the  oppo- 
site sex  are  unusually  developed.  It  is  needless  to  say  that  such 
individuals  are  not  the  best  parents. 


II— INTERNAL    INFLUENCES   AFFECTING    THE 
RACE  AS  A    WHOLE 

Over  against  those  causes  that  may  operate  in  the  case  of 
each  individual  to  warp  its  development  are  to  be  considered 
those  that  influence  the  race  as  a  whole,  turning  the  line  of 
descent  more  or  less  permanently  aside  from  former  channels. 
Some  of  these  influences  are  clearly  denned  and  easily  recog- 
nized ;  others  are  problematical,  the  discussion  not  having  yet 
passed  beyond  the  stage  of  a  plausible  theory. 

The  student  of  thremmatology  and  the  breeder  should  be 
always  mindful  that  the  purpose  of  all  good  breeding  is  not  simply 
to  hold  what  we  already  have  but  to  produce  new  types  better 
adapted  than  the  old  to  the  purposes  of  man.  Accordingly  any 
and  all  lines  that  promise  any  hope  of  success  should  be  assidu- 
ously investigated. 

SECTION  XI  — RELATIVE  FERTILITY,  OR  GENETIC 
SELECTION  2 

The  assumption  that  all  members  of  a  race  are  equally  fertile 
in  se  and  inter  se  (of  themselves  and  between  each  other  in  all 
directions)  is  not  only  hasty  but  dangerously  incorrect.  To 
quote  Pearson,  "  Fertility  is  not  equally  distributed  among  alJ 
individuals." 

1  The  entire  animal  with  increasing  age,  its  own  sexual  characters  abating, 
begins  to  take  on  those  of  the  other  sex.    Thus  the  hen  grows  spurs,  the  cow 
bellows  and  paws  the  dirt,  women  grow  scanty  beards,  and  old  men's  voices  gro\v 
light. 

2  Pearson,  Grammar  of  Science,  pp.  376,  414,  437-449,  462. 


INTERNAL   CAUSES  OF  VARIATION  197 

If  this  be  true,  and  practical  breeders  know  that  it  is  true, 
then  an  interesting  and  important  question  at  once  arises ; 
namely,  What  characters  are  correlated  with  the  highest  fertility  ? 
This  is  important,  because  these  are  the  ones  that  will  become 
the  dominant  characters  of  the  race,  certainly  unless  opposed  by 
the  most  rigid  selection  or  by  other  powerful  influences.  This 
is  genetic  selection,  —  an  ever-present  influence  over  the  line  of 
descent,  tending  to  establish  what  might  be  called  a  natural  type. 

Unfortunately  we  possess  no  accurate  data  on  this  point 
among  domestic  animals,  but  Pearson's  work  x  among  men  and 
plants  is  sufficient  to  settle  the  principle  that  such  a  definite 
influence  exists. 

He  finds,  for  example,  that  daughters  are  not  taller  than 
their  mothers,  but  that  they  are  taller  than  wives  in  general. 
Now  not  all  wives  are  mothers,  and  these  data  mean  simply 
that  taller  women  are  on  the  average  more  fertile.  There  is 
thus  some  correlation  between  fertility  and  stature.  This  is 
genetic  selection,  and  under  it  the  stature  of  women  (English) 
may  be  expected  to  gradually  increase  until  such  correlation  is 
satisfied,  unless  held  back  by  other  influences. 

Mothers  are  less  variable,  but  daughters  more  so,  than 
wives  in  general ;  that  is,  progressive  selection  exists,  for  not 
all  daughters  marry,  and  not  all  who  marry  produce  young. 
If  the  standard  deviation  from  the  race  were  the  same  for  each, 
then  no  selection  would  be  involved,  but  it  is  progressively  less 
from  daughter  to  wife  and  on  to  mother.  The  difference  between 
daughter  and  ivife  is  due  to  preferential  mating,  the  especially 
ugly  individuals  being  less  likely  to  find  a  mate  ;  but  the  differ- 
ence between  wife  and  mother  is  due  to  relative  fertility. 

The  fact  that  in  general  the  mother  is  nearer  the  average 
than  is  the  wife  shows  that  the  race  is  fairly  stable ;  but  the 
fact  that  wives  are  shorter  than  mothers  has  but  one  meaning,  — 
that  in  respect  to  stature  the  race  is  yet  unstable. 

Extensive  studies  in  eye  color  indicate  that  dark-eyed  indi- 
viduals, both  men  and  women,  are  slightly  more  fertile  than  are 
the  lighter-eyed.  This  means  that  the  dark-eyed  will  progress 
(increase)  upon  the  light-eyed  and  the  race  will  grow  darker-eyed, 

1  Pearson,  Grammar  of  Science,  pp.  441-445. 


198  CAUSES  OF  VARIATION 

unless  the  tendency  shall  be  held  in  check  by  the  greater  attract- 
iveness of  lighter  eyes,  — preferential  mating.  This  would  be  a 
long  and  slow  process,  but  it  would  avail  much  to  reduce,  though 
it  could  never  overcome,  the  effects  of  the  higher  fertility  of  the 
darker-eyed  individuals. 

Pearson  collected  4443  capsules  of  wild  poppy.1  They  showed 
the  following  distribution  arranged  according  to  the  number  of 
stigmatic  bands  : 


Bands  .... 
Frequency  .  . 

5 

i 

6 
IT 

7 
32 

8 
56 

9 
148 

10 

363 

1  1 
628 

12 

925 

13 

954 

14 
709 

15 

397 

16 
155 

17 
Si 

18 

12 

19 
I 

The  largest  number  of  capsules  (954)  had  13  bands  and  the 
next  largest  number  had  12.  Very  few  had  so  many  as  18  or  19, 
or  so  few  as  5,  6,  or  7.  The  type  number  of  bands  is  then  13. 

He  provided  receptacles  and  kept  the  seeds  of  each  group 
separate.  He  says  : 

To  my  great  surprise,  however,  my  receptacles  for  12  and  13  were 
filled  up  with  the  contents  of  very  few  capsules,  those  for  1 1  and  14  more 
tardily,  those  for  10  and  15  only  with  emptying  a  great  number  of  capsules, 
while  I  could  hardly  get  any  seed  at  all  from  those  capsules  with  very  many 
or  very  few  bands ;  they  were  practically  sterile.  The  type  capsules  were 
enormously  fertile,  [while]  those  with  even  a  moderate  deviation  from  it 
[were]  relatively  or  even  absolutely  infertile.2 

This  being  true,  the  poppy  has  become  about  as  stable  as  is 
possible,  for  its  highest  fertility  is  with  its  most  numerous  popu- 
lation. This  plant  was  growing  wild  in  nature.  Obviously  the 
great  bulk  of  seeds  distributed  would  be  of  the  type  number,  1 3 
or  near  it,  and  the  mass  of  descendants  would  arise  from  seeds 
close  to  the  type.  What  chance  now  would  there  be  in  nature 
for  a  large  colony  of  six-or  seven-banded  strains  to  arise  ?  Very 
little,  unless  they  happened  to  possess  some  decided  advantage 
in  the  struggle  for  existence,  in  which  case  the  type  would 
speedily  shift  in  that  direction;  but  as  long  as  "the  highest 
fertility  remained  with  the  higher  number  of  bands,  the  race 
would  be  unstable. 

1  Pearson,  Grammar  of  Science,  pp.  443-444. 

2  Ibid.  p.  444. 


INTERNAL  CAUSES  OF  VARIATION 


199 


Suppose  it  were  the  purpose  of  man  to  develop  a  poppy  with 
fewer,  or  with  more,  than  the  natural  number  of  bands,  —  say 
seven  or  seventeen.  Under  what  disadvantage  he  would  work 
as  long  as  the  fertility  remained  relatively  low !  and  he  would 
never  succeed  unless  he  separated  the  plantings  from  the  more 
prolific  type.  This  is  genetic  selection. 

Breeders  are  constantly  operating  against  the  drag  of  infertility 
without  knowing  it,  and  are  as  often  wondering  why  better 
results  do  not  follow,  especially  when  only  approved  mating 
is  practiced.  Consider  the  mathematics  involved  in,  say,  three 
lines  of  descent  of  different  degrees  of  prolificacy.  For  the 
sake  of  simplicity  in  illustration  let  us  suppose  three  cows  were 
living  in  a  herd  together.  One  of  these  cows  raises  two  calves 
and  becomes  barren ;  another  raises  four  before  she  ceases  to 
breed,  and  another  six.  For  the  sake  of  further  simplicity  let  us 
suppose  that  one  half  the  calves  are  females,  and  that  each 
daughter  descendant  exactly  repeats  the  performance  of  her 
dam  and  then  becomes  barren.  How  will  the  account  stand  in 
a  few  generations  ? l 

CUMULATIVE  EFFECTS  OF  FERTILITY  AS  SHOWN  BY  THE  RELATIVE 

NUMBER  OF  FEMALE  DESCENDANTS  OF  Cows  OF  VARIOUS 

DEGREES  OF  FERTILITY 


GENERATIONS 

Cows 

CALVES 

< 

2 

3 

4 

5 

No.  i 

2 

, 

, 

I 

I 

I 

No.  2 

4 

2 

4 

8 

16 

32 

No.  3 

6 

3 

9 

27 

81 

243 

This  tabular  presentation  shows  that  after  five  generations 
of  this  kind  of  breeding  there  would  be  but  one  fertile  cow  of 
the  first  order  in  the  herd,2  while  if  all  had  been  kept  there 
would  be  32  of  the  second  order  and  243  of  the  third.  What  an 

1  There  is  no  longer  any  doubt  that  fertility  is  an  inheritable  character. 

2  There  might  be  any  number  of  living  barren  ones  if  the  strain  happens  to  be 
a  favorite  and  is  long-lived. 


200  CAUSES  OF  VARIATION 

opportunity  for  selection  in  the  latter  instance,  with  none  what- 
ever in  the  former !  The  first  untimely  death  would  render  the 
line  extinct,  which  is  perhaps  the  best  fate  that  could  overtake 
a  race  which  at  best  is  able  only  to  hold  its  initial  number  good. 

Of  course  artificial  conditions  have  been  assumed  in  order  to 
bring  out  the  principle.  It  does  not  work  out  in  this  regular 
and  evident  manner  in  our  herds,  but  the  principle  of  genetic 
selection  is  at  work,  nevertheless.  It  would  be  fortunate  if  it 
were  more  evident,  for  the  herds  are  few  that  do  not  contain  a 
large  proportion  of  females  that  contribute  nothing  to  the  real 
line  of  descent,  though  they  now  and  then  give  birth  to  excep- 
tional individuals.  The  quality  is  good,  but  the  rate  of  repro- 
duction is  too  low. 

How  many  a  breeder  has  spent  fruitless  years  in  ineffectual 
attempts  to  build  up  a  strain  excellent  in  itself  but  essentially 
infertile  !  Witness  the  fate  of  that  remarkable  family  of  short- 
horns, the  Duchess.  This  famous  family,  in  its  glory,  was  never 
surpassed,  yet  it  was  genetic  selection  that  exterminated  the 
line.  Fortunate  indeed  is  the  breeder  who  knows  this  principle 
and  realizes  its  full  power  whenever  he  finds  himself  opposed 
by  it. 

The  student  must  not  get  the  impression  that  genetic  selec- 
tion is  an  enemy  only.  A  prolific  line  tends  as  strongly  to 
establish  and  maintain  itself  as  does  a  barren  one  to  rush  head- 
long to  extinction.  Genetic  selection  is  therefore  a  friend  pow- 
erful for  good,  as  well  as  an  enemy  powerful  for  evil ;  but  it  is 
as  quiet  and  unobtrusive  in  the  one  relation  as  it  is  insidious 
•in  the  other.  The  breeder  has  only  to  be  eternally  conscious  of 
the  fact  that  if  he  is  to  succeed  he  must  have  numbers,  not 
occasional  births,  but  regular  and  generous.  Then  he  may  be 
sure  that  he  is  not  trying  to  do  a  thing  on  which  nature  has 
set  the  seal  of  her  disapproval  through  non-production.  However 
worthy  and  however  valuable  intrinsically  the  strain  may  be,  it  is 
worthless  unless  he  can  produce  it  with  certainty  and  in  any 
desired  numbers.  "  Beware  of  the  shy  breeder,  and  treasure  the 
old  female  that  breeds  regularly  and  true."  This  doctrine  estab- 
lishes a  cooperation  with  nature  that  insures  results,  and  with- 
out it  genetic  selection  will  work  against  us,  not  for  us. 


INTERNAL  CAUSES  OF  VARIATION  20 1 

SECTION  XII  —  PHYSIOLOGICAL  SELECTION 

The  term  "  physiological  selection  "  refers  to  the  fact  that  cer- 
tain individuals,  fertile  enough  of  themselves,  will  yet  absolutely 
fail  to  breed  with  a  particular  individual  of  the  opposite  sex.1 

This  principle  is  now  well  established  and  is  recognized  as  a 
large  cause  of  fruitless  marriages.  Individuals  are  frequently 
barren  in  one  marriage  and  perfectly  fertile  in  another.  Physio- 
logical selection  is  a  phase  of  genetic  selection,  and  while  of 
extreme  importance  in  the  marriage  relation  it  constitutes  no 
special  menace  to  our  herds.  In  general  it  has  little  bearing 
upon  the  development  of  a  breed,  but  is  often  exceedingly 
troublesome  when  it  is  desired  to  effect  a  particular  combination 
of  blood  lines. 


SECTION  XIII  — SELECTIVE  DEATH  RATE;   LONGEVITY 

The  total  population  depends  as  much  upon  longevity  as  upon 
fertility  and  the  prevailing  type  at  any  moment  depends  as  much 
upon  the  individuals  that  die  out  of  the  world  as  it  does  upon 
those  that  are  brought  into  it. 

If  the  draft  by  death  is  equal,  or  rather  proportional,  from  all 
types  of  the  race  or  breed,  then  the  existing  type  will  be  the 
same  as  that  born  into  the  world  ;  if  not,  it  will  be  different. 

As  there  is  little  use  in  attempting  to  breed  a  strain,  however 
desirable,  that  is  not  at  least  fairly  prolific,  so  there  is  little  use 
in  spending  time  and  expense  upon  short-lived  strains,  especially 
of  milch  cows  and  horses,  which  are  valuable  largely  in  propor- 
tion to  age. 

For  reproductive  purposes  the  "  age  "  of  an  animal  is  the  age 
at  which  he  stops  breeding,  but  for  other  purposes  it  is  the  age 
at  which  he  can  no  longer  render  valuable  service  in  the  desired 
direction,  such  as  labor. 

1  This  principle  was  first  announced  by  Romanes  ("  Physiological  Selection," 
Journal  of  the  Linnccan  Society,  XIX,  337-41 1),  though  what  he  had  in  mind  evi- 
dently included  what  is  now  known  as  "genetic  selection."  It  was  proposed  as 
showing  that  other  principles  are  at  work  to  fix  types,  aside  from  the  struggle  for 
existence. 


202  CAUSES  OF  VARIATION 

Weismann x  believes  that  in  nature  the  death  point  has  been 
fixed  at  an  age  most  profitable  to  the  race  as  a  whole.  That  is 
to  say,  it  is  best  for  the  race  (i)  that  only  the  strongest  should 
survive  to  the  breeding  age ;  (2)  that  these  should  live  as  long 
as  they  are  able  to  reproduce;  and  that  (3)  they  should  then  die 
and  cease  to  occupy  room  and  consume  food  which  would  other- 
wise be  available  for  the  sustenance  of  more  robust  individuals 
engaged  in  reproduction.  This  fixes  the  death  point  theoretic- 
ally at  the  cessation  of  reproduction,  except  in  such  species  as 
those  in  which  the  young  need  the  care  or  the  educative  assist- 
ance of  the  mother.  In  these  the  theoretical  death  point  would  be 
at  the  maturity  of  the  last  young.  This  of  course  is  in  reference 
to  wild  species,  and  Weismann  believes  that  nature  has  estab- 
lished the  death  point  in  close  correspondence  to  this  principle. 

However  that  may  be,  there  is  a  problem  here  for  the  breeder. 
It  is  for  him  to  fix  the  death  limit  well  beyond  the  period  of  the 
particular  service  required.  In  nature  there  is  but  one  object  in 
life, —  self-preservation  and  reproduction.  On  our  farms  there 
are  other  objects.  The  horse  is  for  labor,  and  his  serviceable 
age  as  well  as  his  degree  of  intelligence  needs  to  be  lengthened 
as  much  as  possible.  In  nature  early  and  rapid  reproduction  is 
a  full  equivalent  for  longevity.  It  is  not  so  on  our  farms,  where 
the  individual  counts  for  more,  and  even  rapid  reproduction 
cannot  take  the  place  of  long  life  and  faithful  service. 

SECTION  XIV  — BATHMIC   INFLUENCES 

Do  species  possess  inherent  tendencies  to  vary  ?  If  a  race 
could  be  surrounded  by  positively  unchanging  conditions,  if  it 
could  produce  asexually,  and  if  all  types  were  equally  vigorous 
and  equally  fertile,  would  it  remain  constant?  Some  variation 
would  arise  through  reduction,  but  this  would  be  heterogeneous, 
—  that  is,  now  in  one  direction,  now  in  another.  The  real  ques- 
tions the  bathmic  evolutionist  asks  are  these  :  Is  there  a  tend- 
ency for  the  type  to  drift,  independent  of  selection  or  surrounding 
influences  ?  Are  its  deviations  characterized  by  a  continual  bias 

1  Weismann,  Essays  on  Heredity,  T,  111-163;  see  also  Pearson,  Chances  of 
Death,  pp.  1-42. 


INTERNAL  CAUSES  OF  VARIATION  203 

in  favorite  directions  ?  Does  it  vary  progressively  because 
impelled  in  these  directions  by  "growth  force"  or  other  inherent 
energy  ?  Are  species  held  to  their  present  standards  by  outside 
influences  ?  or,  if  not  "  held,"  are  they  drifting  in  spite  of  us  ? 
Is  the  life  principle  constant  or  periodic  in  its  activities ;  and 
are  those  internal  energies  that  vitalize  matter  and  that  determine 
development  and  differentiation, — are  they  indifferent  as  to  the 
trend  of  the  type,  or  do  they  run  more  easily  in  some  channels 
than  in  others  ?  Is  variation  in  some  sense  subject  to  and  directed 
by  a  natural  bias  ?  This  is  the  field  of  bathmic  evolution,1  and 
these  are  the  questions  involved.  No  one  is  more  interested  in 
their  discussion  than  is  the  breeder  of  domesticated  forms. 

Two  principal  theories  covering  the  field  of  bathmic  evolution 
have  been  proposed,  both  incapable  of  absolute  proof,  as  all  such 
theories  must  be,  but  both  of  interest  to  the  breeder. 

Acceleration  or  retardation  of  growth  force.  This  principle  is 
announced  by  Cope2  as  an  internal  and  ever-present  cause  of 
progressive  evolution,  running  through  all  forms  of  life  and 
beneath  all  ordinary  influences,  impelling  unnoticeably  but  irre- 
sistibly in  certain  directions.  It  is,  after  all,  according  to  this 
author,  the  most  subtle  and  most  potent  cause  of  departure  from 
type.  The  horse  has  undergone  steady  progressive  development 
from  an  animal  of  the  size  of  a  jack  rabbit  up  to  his  present 
proportions  and  perfection.  This  is  due,  according  to  Cope, 
not  so  much  to  selection  as  to  a  continuous,  perhaps  almost 
unprecedented,  acceleration  of  growth  force. 

This  theory  attempts  to  explain  much  of  evolution  through 
the  energy  of  growth,  thus  throwing  into  the  discussion  a 
dynamic  element  commonly  neglected  by  evolutionists.  In  this 
connection  Pearson  pertinently  remarks  : 

There  is  nothing  more  (or  less)  unscientific  in  using  an  inherent  growth 
force  to  explain  the  secular  changes  in  living  forms  than  in  using  the  force 
of  gravitation  inherent  in  matter  to  explain  the  development  of  planetary 

1  Pearson,  Grammar  of  Science,  pp.  375-377.    The  term  "bathmic"  as  here 
used  does  not  include  genetic  selection  or  any  other  selective  agent,  internal  or 
external,  because  the  effects  of  all  such  influences  tend  to  come  to  a  rest  and 
not  to  constitute  a  "continual  bias." 

2  Cope,  Origin  of  the  Fittest,  pp.  18-30,  190-192,  396-398;  Primary  Factors 
of  Organic  Evolution,  pp.  473-494. 


204  CAUSES  OF  VARIATION 

systems  from  nebulae.  The  ultimate  action  of  vital  units  in  each  other's  pres- 
ence would  be  no  more,  nor  less,  of  a  mystery  than  the  ultimate  action  of 
material  units.  .  .  .  The  real  objection  to  bathmic  evolution  lies  not  in  any 
a  'priori  reason  against  an  inherent  growth  force,  but  to  the  obvious  histor- 
ical fact  that  such  a  force  has  been  used  to  cover  all  sorts  of  obscure  reason- 
ing and  even  sheer  foolishness.  Science  would  welcome  above  all  things  a 
description  of  the  action  between  vital  units  as  simple  as  the  law  of  gravi- 
tation, provided  it  gave  a  causal  account  of  variation;  and  the  welcome 
would  be  none  the  less  sincere  if  the  action  showed  that  variation  was  biased 
and  that  evolution  would  be  irreversible  even  with  a  reversed  sequence  of 
physical  environments.1 

Cope's  theory  of  acceleration  or  retardation  of  growth  force 
is  of  course  merely  quantitative,  and  would  explain  any  differences 
that  might  arise  through  either  size  or  proportions  of  parts,  or 
faculties  dependent  upon  such  proportions.  It  does  not  attempt 
to  explain  the  introduction  of  characters,  and  if  it  can  be  in  any 
way  controlled  no  method  has  yet  been  pointed  out. 

We  all  allude  to  the  same  general  thought  when  we  use  the 
words  "  vitality  "  and  "  constitution  "  to  denote  not  so  much  ten- 
acity of  life  as  vigor  of  growth,  and  we  all  recognize  that  some 
individuals  and  some  lines  possess  this  faculty  in  much  higher 
degree  than  others.  Some  individuals  never  survive  the  embry- 
onic stage  ;  others  die  in  infancy  ;  still  others  reach  full  maturity, 
and  a  few  persist  to  an  advanced  age.  As  death  comes  only  with 
the  failure  of  some  vital  function,  the  individual  may  persist  long 
after  he  is  stripped  of  everything  that  makes  life  enjoyable. 

It  is  so  with  races.  Some  seem  endowed  with  phenomenal 
vigor,  while  others  are  preserved  from  extinction  only  with  the 
greatest  difficulty  and  by  the  narrowest  margin,  not  only  because 
of  low  fertility  but  also  by  reason  of  inherent  lack  of  vigor.  The 
existence  of  these  internal  forces  is  not  a  matter  of  doubt,  and  their 
office  in  directing  variation  is  an  interesting  and  valuable  problem 
which  the  present  state  of  knowledge  is  insufficient  to  solve. 

Orthogenesis.*  Closely  akin  to  Cope's  conception  is  Eimer's 
theory  of  orthogenesis2  (straight  creation),  or,  as.  he  calls  it, 
"definitely  directed  evolution." 

1  Pearson,  Grammar  of  Science,  pp.  375-376. 

3  Eimer,  On  Orthogenesis  and  the  Importance  of  Natural  Selection  in  Species- 
Formation  (pamphlets,  56  pages)  [Open  Court  Publishing  Company]. 


INTERNAL  CAUSES  OF  VARIATION  205 

This  theory  of  Elmer's  is  put  forth  as  a  protest  and  a  counter 
proposition  to  the  theory  of  Darwin,  —  afterward  very  much 
elaborated  and  extended  by  Weismann  and  others,  —  which  was 
to  the  effect  that  all  evolution  is  the  result  of  heterogeneous 
growth  trimmed  down  and  shaped  up  by  the  extinction  of  indi- 
viduals possessing  unfavorable  characters.  The  natural  assump- 
tion of  the  extreme  selectionists  is  that  utility  is  the  basis  of 
all  selection,  and  that  only  useful  characters  will  be  preserved, 
the  inevitable  corollary  of  which  is  that  all  existing  characters 
are  useful. 

Now  the  necessary  consequence  of  selection  is  that  after  a 
time  all  existing  forms  and  characters  will  come  to  "  fit  "  or  agree 
with  the  conditions  of  life,  which  are  the  natural  agents  of  selection. 
This  "fit  "  is  so  accurate  as  to  deceive  many  observers  and  lead 
them  to  declare  selection  to  be  a  fundamental  cause  of  variation. 

Eimer  points  out  two  facts 1 :  first,  that  there  can  be  no  selec- 
tion until  a  choice  is  presented,  —  therefore  that  the  selective 
process  follows  and  does  not  precede  the  origin  of  a  deviation ; 
that  selection  may  and  does  cause  the  race  to  vary,  but  that  it 
has  nothing  to  do  with  the  presentation  of  the  variation  in  the 
first  individual,  — a  position  in  which  he  is  certainly  correct. 

He  argues,  second,  that  it  is  not  true  that  all  characters  are 
useful,  but  that  many  species  endure  those  that  are  inconvenient 
and  unfortunate,  yet  not  sufficiently  detrimental  to  be  fatal,  else 
the  line  would  become  extinct  and  no  such  instances  would  ever 
be  seen. 

His  position  is  that,  first  of  all,  "  organisms  develop  in  definite 
directions  without  the  least  regard  for  utility,  through  purely 
physiological  causes,  and  as  the  result  of  organic  growth''  2 

Then,  after  all  the  characters  have  developed  together,  they 
are  passed  upon  by  natural  selection  in  the  struggle  for  existence, 
this  process  blotting  out  only  those  sufficiently  detrimental  to 
unfit  the  individuals  so  afflicted  for  continuing  the  struggle  in 
competition  with  more  favored  forms.  Selection  does  not  remove 
a  handicap,  or  relieve  a  race  from  all  undesirable  characters. 
It  eliminates  only  the  worst,  and  down  to  a  level  sufficient  to 
establish  a  kind  of  "equilibrium  of  life." 

1  Eimer,  Organic  Evolution,  sects,  ii  and  iii.         2  Eimer,  On  Orthogenesis,  p.  2. 


2o6  CAUSES  OF  VARIATION 

In  this  view  of  the  case  characters  bad  and  good  develop 
together.  The  worst  ones  are  eliminated,  but  many  undesirable 
or  indifferent  ones  are  left  behind  as  not  being  sufficient  to  turn 
the  scale  against  the  individual  or  the  race.  Thus  many  undesir- 
able characters  linger  in  all  races,  and,  what  is  more  to  the  point, 
utility  is  not  the  cause  of  either  the  origin  or  the  persistence  of 
characters,  but  only  of  their  obliteration  when  sufficiently  detri- 
mental to  destroy  the  individual  and  therefore  cut  off  descent  in 
that  particular  line. 

The  writer  shares  the  opinion  that  this  is  the  true  limit  of  the 
selection  process  under  nature,  and  that  the  presence  of  unfavor- 
able characters  argues  for  their  having  arisen  from  causes  quite 
independent  of  selection. 

In  our  yards  and  fields  we  control  selection  according  to  what- 
ever standards  we  may  please  to  establish,  but  if  unfavorable  char- 
acters develop  in  nature,  where  selection  aims  directly  at  life,  will 
they  not  be  likely  to  develop  also,  unnoticed,  under  our  own  selec- 
tion, especially  when  we  do  all  within  our  power  to  preserve  life  P1 

The  presence  or  absence  of  a  principle  aside  from  selection, 
yet  responsible  for  the  presence  of  characters,  turns  very  largely 
upon  the  question  as  to  whether,  after  all,  there  are  well-established 
instances  of  characters  independent  of  utility,  and  therefore  of 
selection.  The  presence  of  such  characters  is  easily  shown.  For 
example,  what  is  the  utility  of  the  scrotum  among  mammals  ? 
Would  it  not  have  been  better  with  sheep,  for  instance,  if  the 
testicles  had  remained  within  the  abdominal  cavity,  where  they 
develop,  and  where  they  would  be  safe,  instead  of  descending 
into  an  external  sack  exposed  to  frequent  injury  ?  Undoubtedly 
it  would  have  been  better  for  individuals,  for  many  have  not  only 
lost  these  organs,  but  their  lives  as  well,  from  this  unfortunate 
position  ;  but  the  number  lost  is  not  sufficient  to  seriously  affect 
the  race?'  In  other  words,  selection  has  aimed  at  this  vulnerable 

1  It  is  noticeable  that  nature  allows  reproduction  to  go  on  unrestricted,  and 
then  slays  by  the  millions.   Man  cannot  afford  this  wholesale  destruction  of  num- 
bers.   He  seeks  to  prevent  undesirable  births,  —  a  kind  of  advance  selection  that 
has  both  its  advantages  and  its  disadvantages. 

2  This  shows  that  what  is  bad  for  the  individual  is  not  necessarily  bad  for  the 
race  ;  conversely,  what  is  best  for  the  race  is  often  hard  upon  or  even  fatal  to  the 
individual.    This  is  the  very  essence  of  selection. 


INTERNAL  CAUSES  OF  VARIATION  207 

point  many  times,  and  in  numerous  cases  with  effect,  but  mam- 
mals as  a  race  have  been  able  to  endure  the  handicap,  else  they 
would  long  since  have  become  extinct. 

This  shows  that  some  causes  other  than  utility  are  responsible 
for  the  appearance  and  continuance  of  racial  characters;  that 
teleology1  is  not  a  universal  principle,  and  that  the  function  of 
selection  is  restrictive,  not  creative. 

Other  characters  not  teleological  may  easily  be  mentioned  : 

1.  The  peculiar  minute  markings  on  diatoms  and  on  other 
inconspicuous  organisms. 

2.  The  green  color  of  leaves,  due   simply  to  the  fact  that 
chlorophyll  is  green.    This  is  no  more  of  an  inherent  necessity 
than  that  coal  should  be  black  or  gold  yellow. 

3.  The  digital    number    five  which    runs    generally  through 
vertebrates,  which  has  often  been  modified  and  often  left  intact. 
Certainly  the  original  number  five  could  not  have  been  teleolog- 
ical.   It  is  not  enough  to  assume  that  changed  conditions  might 
have    rendered  an  organ  detrimental   which    was  once   useful. 
There  are  too  many  obviously  useless  characters. 

4.  The  phosphorescence  of  pelagic  animals,2  and  the  pearl  of 
the  oyster,  which  is  due  to  injury.    Is  this  beauty  useful  or  is  it 
accidental  ? 3 

5.  The  bright  color  of  deep-sea  fishes.    Is  it  any  more  signifi- 
cant than  the  (accidental)  color  of  chlorophyll-bearing  leaves  ?  * 

6.  The  horns  of  stags,  —  useful  (?)  in  battle,  but  weapons  as 
dangerous  to  the  possessor  as  to  his  enemy. 

The  list  might  be  extended  indefinitely.  Eimer 's  argument  is 
that  characters  such  as  these  have  been  produced  not  through 
selection  but  in  spite  of  it,  and  through  the  agency  of  organic 
growth  in  definite  directions,  which  is  orthogenesis.  It  w.ould  be 
difficult  to  be  always  certain  that  no  basis  of  utility  exists  or 
ever  has  existed  simply  because  it  is  not  now  evident,  yet  no 

1  The  doctrine  that  development  is  in  line  with  utility  and  that  everything  is 
useful  is  known  as  "  teleology." 

2  Eimer,  Organic  Evolution,  p.  xiii. 

3  Eimer,  Orthogenesis,  p.  10. 

4  In  certain  leaves  of  bright  color  the  chlorophyll  is  unable  to  dominate  the 
stronger  shades  of  other  chemical  substances,  and  the  leaf  is  not  green  but  some 
other  color. 


208  CAUSES  OF  VARIATION 

careful  student  of  evolution  doubts  any  longer  that  there  are 
many  misfits  in  nature.  Whether  they  have  arisen,  as  Eimer 
asserts,  by  reason  of  organic  growth,  and  whether  they  are  evi- 
dences of  definitely  directed  deviation,  is  quite  another  matter. 

There  is  no  doubt  of  the  persistence  of  a  character  once  started, 
even  in  the  face  of  selection,  but  whether  it  be  necessary  to 
invoke  the  aid  of  an  internal  directive  force  to  explain  it  is  a 
question  upon  which  more  evidence  is  sorely  needed.  It  is 
exceedingly  important  for  the  breeder  to  know  and  recognize  all 
the  inherent  tendencies  with  which  he  must  finally  reckon,  and 
it  may  be  necessary  to  go  beyond  physiological  units,  correspond- 
ing to  chemical  atoms  or  molecules,  and  invoke  some  form  of 
"growth  force  "  corresponding  to  chemical  energy  to  explain  the 
mysteries  of  development.  Any  theory,  however,  that  will  even 
reasonably  account  for  these  mysteries  must  be,  in  the  present 
state  of  knowledge,  largely  an  assumption,  and  let  the  assump- 
tion be  as  simple  as  possible  until  we  can  defend  its  complexity 
by  a  mass  of  well-established  facts.  In  the  opinion  of  the  writer 
the  existence  of  such  a  principle  as  orthogenesis  is  more  than 
problematical,  except  as  it  is  an  expression  of  the  relations 
that  naturally  obtain  between  physiological  units,  whatever  they 
may  be. 

SECTION   XV  —  PHYSIOLOGICAL   UNITS 

The  "gemmules"  of  Darwin,  the  "  stirp "  of  Galton,  the 
"idioplasm"  of  Nageli,  the  "biophors,"  "determinants,"  and 
"ids"  of  Weismann,  and  the  "  physiological  units"  of  other 
writers  are  all  attempts  to  explain  inheritance  of  definite  quali- 
ties by  assuming  that  the  germ  cell  which  passes  over  from 
parent. to  offspring  at  the  time  of  procreation  is  composed  of 
definite  units  of  living  matter,  each  with  its  specific  properties, 
among  which  are  nutrition  and  multiplication,  which  together 
constitute  growth,  and — considering  the  separate  properties  of 
the  different  units  of  which  a  given  individual  is  composed  — 
growth  in  definite  directions. 

In  support  of  this  general  theory  it  may  be  urged  that  the  indi- 
vidual is  what  he  is  very  largely  because  of  internal  qualities. 
Corn  and  wheat  grow  side  by  side,  drawing  their  nourishment 


INTERNAL  CAUSES  OF  VARIATION 


209 


from  the  same  soil  and  the  same  atmosphere.  The  most  nour- 
ishing food  and  the  most  deadly  poison  are  produced  side  by 
side  under  identical  external  conditions.  A  man  divides  his 
dinner  with  his  dog :  one  portion  simply  nourishes  the  dog 
and  provides  energy  to  watch  sheep  or  perchance  to  kill  them  ; 
the  other  results  in  strength  to  bless  the  ages,  or  perhaps  in 
crime  to  shock  the  world,  —  each  according  not  to  the  nature 
of  the  food  but  to  that  of  the  animal  that  consumes  it,  and 
to  the  support  of  whose  peculiar  energies  it  contributes. 

This  kind  of  difference  in  living  organisms  is  traceable  to  the 
endowments  of  a  single  cell,  —  the  only  material  that  passes 
over  from  parent  to  offspring,  —  and,  regard  it  as  we  may,  we 
must  see  in  this  single  bit  of  living  matter  all  the  potential 
qualities  of  the  race,  all  the  differences  between  the  corn  and 
the  wheat,  between  the  man  and  his  dog.  They  are  all  there, 
represented  in  some  material  way  in  the  constitution  of  the 
germ  cell.  There  is  thus  a  material  basis  to  heredity. 

We  must  accept  one  horn  or  the  other  of  the  dilemma : 
either  conceive  this  single  cell  as  directly  endowed  with  all  the 
qualities  of  the  race,  defining  its  development,  or  else  endow  it 
with  the  capacity  to  develop  in  this  fashion  or  that  according 
to  stimuli.  But  whence  come  the  stimuli  ?  Certainly  not  alto- 
gether from  without,  or  the  man  and  his  dog  would  become 
alike,  if  consuming  the  same  kind  of  food  ;  and  to  assume  that 
the  influences  are  internal  is  only  to  push  the  puzzle  one  step 
farther  away  and  to  assume  possibly  an  immaterial  in  place  of  a 
material  basis. 

The  most  simple  and  direct  explanation  of  the  phenomena  of 
inheritance  and  definite  development  is  to  consider  the  germinal 
matter  as  consisting  of  units  of  some  sort  endowed  with  life 
and  the  power  of  growth.  This  assumption  of  the  physiological 
unit  is  not  so  violent  nor  so  different  from  other  accepted  scien- 
tific assumptions  as  it  at  first  may  seem.  In  the  non-living 
world  we  assume  the  existence  of  the  atom,  whatever  its  ulti- 
mate constitution,  as  a  minute,  indivisible,  and  indestructible 
unit  of  matter.  The  association  of  some  millions  of  like  atoms 
makes  a  measurable  quantity  of  an  element  like  gold,  silver, 
iron,  chlorin,  or  sodium. 


2io  CAUSES  OF  VARIATION 

Something  over  eighty  distinct  kinds  of  matter  are  known ; 
therefore  some  eighty  kinds  of  atoms  are  assumed,  and  this  ex- 
hausts the  possibilities  so  far  as  unlike  like  atoms  are  concerned 
(unless  other  atoms  are  subsequently  discovered  or  created). 

But  this  does  not  exhaust  the  possibilities  of  matter,  for  these 
atoms  combine  together,  forming  new  units  (called  molecules) 
with  distinct  properties.  Thus  NaCl  (sodium  chlorid)  is  differ- 
ent in  every  way  from  either  the  sodium  or  the  chlorin  atoms 
that  have  united  to  produce  it.  In  this  way  these  (eighty) 
various  atoms  effect  all  sorts  of  combinations,  many  of  them 
exceedingly  complex,1  each  constituting  a  new  material  unit,  a 
sufficiently  large  number  of  which  constitutes  a  measurable 
quantity  of  a  substance  whose  real  composition  could  rarely  be 
predicted  by  any  of  its  visible  properties.  The  following  table 
of  chemical  formulae  is  presented  for  two  purposes  :  (i)  to  show 
the  exceeding  complexity  of  ordinary  materials  ;  (2)  to  show  how 
certain  groups  of  atoms  (as  CH2  or  CO2H)2  behave  as  units, 
effecting  profound  changes  in  the  properties  of  their  compounds. 
It  is  evident  that  the  possible  combinations,  even  with  the  few 
most  common  atoms,  —  as  C,  H,  O,  N,  Fe,  Na,  K,  P,  S,  —  are 
practically  infinite  when  they  are  able  to  organize  themselves 
into  larger  units,  giving  rise  to  complex  series  like  the  table  on 
the  following  page.3 

In  this  table  the  radical  CO2H  runs  through  the  entire  series, 
giving  a  kind  of  genetic  quality  to  the  compounds,  while  specific 
differences  accompany  the  varying  numbers  of  C  and  H  atoms 
present  with  the  radical.  It  is  to  be  noted,  however,  that  these 
C  and  H  atoms  are  in  definite  proportion  to  each  other,  namely, 
CnH2n+1 ;  that  is,  for  every  atom  of  C  there  will  be  one  more  than 
twice  as  many  atoms  of  H,  +  CO2H,  — all  of  which  is  extremely 
suggestive  as  early  steps  in  the  world  of  organized  matter. 

1  The    composition    of    strychnine,    C2iH22N2O2,  and    that  of    grape    sugar, 
Ci2H22On,  are  both   exceedingly  simple  as  compared  with    many  known  sub- 
stances. 

2  Such  groups  of  atoms  that  move  together  are  known  as  "radicals."    They 
are  in  every  sense  units  and  are  capable  of  replacing  or  of  displacing  other  atoms 
in  their  constructions. 

8  We  are  told  by  the  chemists  that  more  than  one  hundred  thousand  separate 
compounds  are  now  known. 


INTERNAL  CAUSES  OF  VARIATION 


21 1 


MONOBASIC  ACIDS  OF  THE  ACETIC  SERIES, 


ACID 

SOURCE 

FORMULA 

Formic  

red  ants,  nettles 

H-CO2H 

Acetic   . 

vinegar 

CH3-CO2H 

oxidation  of  oils  

C2H5-CO2H 

Butyric  .  •    . 

rancid  butter        ... 

C8H7-CO2H 

Valeric  .     .     . 

valerian  root 

C4H9-CO2H 

Caproic      

rancid  butter        

C5Hn'CO2H 

CEnanthic        .... 

oxidation  of  castor  oil 

C6H13tCO2H 

Caprylic     ..... 

C7Hi«:-CO.>H 

Pelargonic      .... 

geranium  leaves        .     .               . 

C8Hi7-CO2H 

Rutic  or  capric    .     .     . 
Euodic  

rancid  butter  f 
oil  of  rue     

C9H19-C02H 
CinH9i*CO9H 

Laurie    ...... 

bayberries                  . 

cocoanut  oil    .     

C12H26-CO2H 

Myristic      

nutmeg  butter           .                    * 

Pentadecylic  .     .     .  .  . 
Palmitic     .     .     .     .     . 

Agaricus  integer  (a  fungus)  .     . 
palm  oil       

Ci4H-29  *  CC^H 

C15H3i-CO2H 

Margaric    

Stearic  . 

tallow 

Balenic 

C  7R3  -CC/H 

Butic      

butter     

Ci9H39-CO2H 

Nardic 

Behenic      

C2iH43-CO2H 

Lignoceric 

beech-wood  tar    ...... 

Hyaenic 

Cerotic  . 

beeswax                                   • 

Melissic      

C29H69-CO2H 

Observe  the  exceeding  complexity  of  these  compounds,  and 
notice  that  they  stand  in  definite  series  with  uniform  differences  ; 
there  are  no  breaks  in  the  series  and  no  missing  members  until 
we  reach  C21H43.  Note  too  that  these  compounds  may  them- 
selves combine  with  others ;  thus  stearin,  the  characteristic  fat 
of  tallow,  is  C3H5  (C18H35O2)3,  in  which  case  3  H  from  the  acid 
radical  and  3  (HO)  from  the  glycerin  radical  have  united  to  form 
3  (H2O),  or  water. 

Above  everything  else  in  this  series  note  the  wide  difference 
in  physical  properties  arising  from  a  slight  difference  in  chemical 


212  CAUSES  OF  VARIATION 

constitution.  For  example,  it  is  significant  that  in  this  series 
both  the  solubility  in  water  and  the  acid  strength  diminish  as 
the  proportion  of  carbon  increases. 

In  addition  to  the  properties  of  non-living  units  the  theory  of 
physiological  units  as  the  basis  for  specific  characters  in  living 
matter  requires  one  distinctive  and  additional  quality,  namely 
life,  with  its  attendant  phenomena,  —  the  power  of  nutrition 
and  growth.  But  what  are  nutrition  and  growth  ?  Considered 
in  general  terms,  nutrition  is  simply  the  power  of  one  chemical 
compound  (the  living)  to  enter  into  the  composition  of  another 
(the  food)  and  break  it  up  and  readjust  its  elements  on  a  basis 
like  its  own,  leaving  the  residues  to  take  care  of  themselves. 

This  readjustment  of  the  non-living  food  to  the  composition 
of  the  living  plant  or  animal  we  call  nutrition,  and  it  means 
essentially  an  increase  of  the  living  at  the  expense  of  the  non- 
living ;  in  other  words,  growth  through  the  numerical  increase 
of  living  units. 

There  is  often  readjustment  in  the  non-living  world  when  two 
compounds  are  brought  together,  —  the  weaker  giving  way  to 
the  stronger  affinity, — but  there  is  no  such  wholesale  ''carry- 
ing over"  of  matter  from  one  to  another  as  in  the  phenomena 
we  call  nutrition  and  growth.  This  is  a  true  invasion  of  the 
non-living  by  the  living  world,  transferring  matter  almost  indef- 
initely, unto  itself,  not  only  preserving  its  own  identity  in  the 
meantime  but  impressing  it  upon  the  appropriated  materials 
as  well. 

These  physiological  or  vital  units  are  therefore  conceived  to 
be  the  smallest  living  units,  like  molecules  in  non-living  matter, 
except  that  they  are  far  more  complex  in  constitution  and  are 
endowed  with  the  power  of  self-multiplication  through  nutrition. 
This  requires  growth  and  division  after  the  manner  which  has 
been  noted  in  chromatin  granules,  except  on  a  scale  infinitely 
more  minute. 

This  conception  of  the  action  of  living  units  has,  its  similitude 
in  the  non-living.  Crystallization  is  a  growth,  in  the  sense  of 
increase  of  size,  but  it  is  not  attended  by  transformations  equal 
to  those  in  living  matter.  Furthermore,  crystallization  is  growth 
without  differentiation,  except  as  to  geometric  form.  Either 


INTERNAL  CAUSES  OF  VARIATION  213 

the  physiological  units  are  capable  of  a  cycle  of  differentiated 
energies,  or  else  the  race  is  possessed  of  many  kinds  of  units, 
each  inactive  until  its  turn,  then  playing  its  role  in  suitable 
order.  What  then  establishes  the  order  of  activity  and  calls 
out  each  unit  at  the  proper  time  ?  Herein  lies  the  mystery,  and 
while  the  physiological  unit  seems  a  biological  fact,  it  after  all 
does  not  solve  the  mystery  of  differentiation  ;  it  only  pushes  the 
problem  one  step  farther  away. 

Unsatisfactory  though  it  is  to  attempt  to  solve  the  mystery 
of  inheritance  and  differentiation  by  means  even  of  vital  units, 
still  nothing  else  that  has  yet  been  proposed  comes  nearer 
satisfying  the  needs  of  the  case,  and  we  cannot  fight  off  the 
following  convictions,  namely  : 

1.  That  there  is  a  material  basis  not  only  of  life  but  of  racial 
characters  as  well,  and  this  material  passes  to  the  individual  by 
means  of  the  germ  cell. 

2.  That  the  processes  of  life  are  essentially  chemical. 

3.  That  if  the  whole  truth  could  be  known,  the  physiological 
units  of  vital  activity  may  not  be  fundamentally  different  from 
atoms,   molecules,  and   radicals  actuated  by  chemical  affinity. 
Broadly  speaking,  there  are  suggestive  similarities  between  the 
chemical  behavior  of  living  matter  and  that  of  laboratory  mate- 
rial generally,  and  these  similarities  are  constantly  turning  up, 
even  where  least  expected. 

Whatever  the  truth  may  be  as  to  the  unit  of  vital  activity,  of 
two  things  we  are  sure  :  first,  there  is  a  unit  of  some  kind,  —  a 
center  of  activity ;  and  second,  it  is  a  chemical  material  pos- 
sessed of  life.  Finally,  to  be  useful,  these  units  must  be 
conceived  as  capable  of  absorbing  nourishment,  and  of  self- 
multiplication  indefinitely. 

SECTION  XVI  — GERMINAL  SELECTION 

The  difficulty  in  seeking  causes  for  inheritance  and  variation 
is  that  we  are  likely  to  prove  too  much.  For  example, "if  suffi- 
cient plasticity  is  assumed  to  fully  account  for  the  high  degree 
of  variation  that  often  occurs,  then  variation  is  sufficiently  pro- 
vided for,  but  this  view  makes  a  thing  like  inheritance  a  matter 


214 


CAUSES  OF  VARIATION 


of  extreme  improbability.1  On  the  other  hand,  if  influences  are 
discovered  which  are  really  efficient  in  setting  bounds  to  varia- 
bility, then  they  make  the  transfer  of  characters  from  parent  to 
offspring  so  absolutely  certain,  regular,  and  fixed,  as  to  seem  to 
leave  little  or  no  possibility  of  variation. 

This  latter  is  the  case  with  the  hypothesis  of  physiological 
units.  Weismann  recognized  its  limitations  and  proposed  the 
theory  of  germinal  selection2  to  account  for  variation  as  well  as 
inheritance. 

This  theory  assumes  that  the  "  biophors,"  or  the  physiological 
units  by  whatever  name  they  may  be  called,  are  engaged  in  a 
kind  of  struggle  among  themselves  within  the  germ,  much  as 
are  plants  and  animals  in  the  larger  world  outside. 

Any  theory  of  physiological  units  must  include  their  absorp- 
tion of  food  and  their  power  of  self-multiplication.  If  these 
activities  proceed  at  a  uniform  rate  for  each  unit  involved,  then 
no  variation  would  result  from  this  multiplication  ;  but  if  propor- 
tions change,  or  if  the  vitality  varies,  then  variation  would  neces- 
sarily result  from  these  causes  alone.  Now  these  activities  must 
be  either  constant  or  variable.  Weismann  assumes  that  they 
are  variable ;  that  these  units  of  various  relative  numbers  and 
strengths  are  competitors  among  themselves,  one  with  another, 
for  food ;  and  that  those  most  energetic  in  food  absorption  and 
capable  of  the  most  rapid  multiplication  will  not  only  be  the 
most  vigorous  but  they  will  also  exist  in  relatively  the  largest 
numbers.  They  will  therefore  tend  the  more  to  impress  their 
characters  upon  the  later  development  of  the  individual. 

Under  this  view  of  the  case  the  "  balance  of  power  "  is  con- 
stantly shifting,  always  in  favor  of  the  most  vigorous  and 
rapidly  multiplying  units.  Believers  in  physiological  units  must 
either  follow  Weismann  in  this  conception  or  else  assume  on 
the  part  of  the  units  absolutely  equal  powers  of  nutrition  and 
multiplication,  for  multiplication  there  must  be  if  such  units 
avail  anything  in  the  r61e  of  inheritance. 

1  All  things  considered,  inheritance  and  not  variation  is  the  mystery.    The 
wonder  is,  not  that  individuals  vary,  but  that  they  follow  as  closely  as  they  do 
the  type  of  the  race  to  which  they  belong. 

2  Weismann,  On  Germinal  Selection  as  a  Source  of  Definite  Variation  (pam- 
phlet, second  edition)   [Open  Court  Publishing  Company]. 


INTERNAL  CAUSES  OF  VARIATION 


215 


Weismann  reminds  us  that  "  by  far  the  largest  part  of 
qualitative  modifications  .  .  .  rest  on  quantitative  changes. 
A  determinant,"  says  he,  "  must  be  composed  of  hetero- 
geneous biophors,  and  on  their  numerical  proportion  reposes, 
according  to  our  hypothesis,  their  specific  nature.  If  this  pro- 
portion is  altered,  so  also  is  the  character  of  the  determinant ; " 
and  further :  "  for  fluctuations  of  nutriment  and  the  struggle 
for  nutriment,  with  its  sequent  preference  of  the  strongest, 
must  take  place  between  the  various  species  of  biophors  as 
well  as  between  the  species  of  determinants.  But  changes  in 
the  quantitative  ratios  of  the  biophors  appear  to  us  qualitative 
changes  in  the  corresponding  determinants."  1  And  again  :  "By 
a  selection  of  the  kind  referred  to  the  germ  is  progressively  modi- 
fied in  a  manner  corresponding  with  the  prodttction  of  a  definitely 
directed  progressive  variation  of the  part !."  2  In  this  way  Weis- 
mann would  "  explain "  Eimer's  orthogenesis ;  but  it  is  note- 
worthy that  none  of  the  theories  yet  proposed  will  account  for  the 
original  introduction  of  a  new  character  in  the  race,  whether 
represented  and  transmitted  by  a  physiological  unit  or  not. 
Germinal  selection  would  provide  for  changes  in  relative  pro- 
portions of  characters,  and  even  for  their  utter  extinction,  but 
not  for  their  introduction,  unless,  indeed,  characters  may  origi- 
nate by  new  combinations  of  old  elements. 

One  is  almost  forced  to  the  conclusion  that  in  nature  loss 
or  modification  of  characters  is  far  more  common  than  their 
origin  and  introduction.  It  looks  as  though  most  of  the  changes 
arise  in  this  way,  yet  it  is  conceivable  that  an  entirely  new 
quality  might  arise  through  a  relatively  slight  modification  of 
the  chemical  or  physiological  make-up  of  the  vital  units.  It  is 
seen  and  recognized  that  in  the  non-living  world  a  slight  change 
in  the  radical  is  followed  by  a  profound  alteration  in  physical 
and  chemical  properties,  and  that  this  sweeping  change  may  be 
induced  by  comparatively  slight  and  even  external  causes. 
May  not  the  same  be  true  of  vital  radicals  or  units,  and  may 
not  new  characters  arise  more  readily  than  we  suppose,  all  per- 
haps out  of  elements  fewer,  and  transformations  simpler,  than 
we  have  hitherto  imagined  ? 

1  Weissman,  On  Germinal  Selection  (second  edition),  pp.  46-47.       2  Ibid.  p.  35. 


216  CAUSES  OF  VARIATION 

Control  of  internal  causes  affecting  the  race  as  a  whole. 
Whatever  causes  of  this  nature  may  be  at  work  in  our  fields 
and  yards, — and  they  are  to  be  reckoned  with,  —  our  control 
over  them  is  secondary  and  indirect.  Their  effects,  if  present, 
are  at  once  insidious  and  sweeping. 

We  can  be  mindful  of  the  effects  of  genetic  selection  and  the 
selective  death  rate,  and  provide  against  them,  at  least  to  a 
large  degree.  If  growth  force  and  orthogenesis  are  also  forces, 
they  can  be  assisted  or  held  in  check  by  selection,  but  they  can 
never  be  absolutely  controlled  ;  and  if  germinal  selection  is  a  fact, 
it  is  going  on  entirely  independent  of  any  control  which  present 
knowledge  enables  us  to  exercise  except  through  selection. 

Summary.  All  that  is  involved  in  heredity  is  contained  in  a 
minute  bit  of  living  matter  passed  from  parent  to  offspring,  and 
whose  development  will  constitute  the  new  individual.  The  im- 
pulse to  development,  therefore,  and  its  fundamental  possibilities 
are  forces  internal  to  the  germ  and  to  the  living  organism. 

It  is  not  difficult  to  see  many  causes  of  variation  in  the 
internal  processes  known  to  be  involved  in  the  activities  of 
living  protoplasm.  Growth  is  the  result  of  cell  division,  which 
seems  to  proceed  upon  plans  calculated  to  insure  qualitative 
as  well  as  quantitative  equality  as  between  the  daughter  cells. 
Any  deviation  from  the  plan,  however, — and  deviations  are 
known  to  occur,  —  must  result  in  variation.  This  is  especially 
true  in  the  reduction  process  which  is  characteristic  of  matura- 
tion in  both  sexes,  and  which  probably  lies  at  the  basis  of  bud 
variation  and  of  many  mutations. 

Fertilization  and  sexual  union  are  processes  calculated  to 
effect  new  combinations  out  of  the  elements  involved,  though 
the  possibilities  in  this  direction  would  be  rapidly  reduced  by 
close  breeding  or  by  any  other  circumstance  which  simplifies 
the  ancestry. 

Doubtless  the  condition  of  the  germ  has  some  influence,  but 
it  is  not  well  understood.  The  phenomenon  of  xenia,  or  double 
fertilization  in  certain  plants,  causes  the  seed  coats  to  vary  the 
first  year  in  the  same  direction  as  the  germ.  Telegony  is  a 
myth,  and  intra-uterine  influences  are  doubtless  limited  to  those 
of  nutrition,  except  in  cases  of  disaster. 


INTERNAL  CAUSES  OF  VARIATION  217 

Reversion  and  atavism  are  but  special  instances  under  the 
law  of  ancestral  heredity  to  be  discussed  later,  serving  to  show 
that  inheritance  is  partly  from  ancestors  back  of  the  parent. 

Certain  internal  factors  are  of  such  nature  as  to  affect  the 
race  as  a  whole.  Genetic  selection  is  based  upon  the  fact  that 
all  individuals  are  not  equally  fertile,  and  that  the  type  tends 
strongly  to  assume  that  of  the  most  prolific.  Bathmic  influences, 
such  as  ''growth  force"  and  orthogenetic  bias,  have  been 
advanced  as  explanations  of  those  inherent  tendencies  that 
appear  to  characterize  most  species  and  that  give  an  underlying 
trend  to  their  direction  in  descent. 

The  basis  of  all  vital  activities  is  conceived  as  being  some 
kind  of  living  unit,  comparable  with  the  atom  and  the  molecule 
in  the  non-living  world,  whose  activities  constitute  growth  and 
differentiation,  and  whose  reactions  with  outside  matter  and 
with  each  other  are  fruitful  causes  of  variation. 

ADDITIONAL  REFERENCES 

BUD  VARIATION  AND  ITS  BEARING  UPON  WEISMANNISM.  By  L.  H. 
Bailey.  Science,  I,  281-291. 

BUD  VARIATION,  CAUSES  OF,  AND  ILLUSTRATION.  By  R.  M.  Kellog. 
Proceedings  of  the  Michigan  Horticultural  Society,  1897,  pp.  121- 
134  ;  also  in  Experiment  Station  Record,  XI,  424-425. 

BUD  VARIATION  OF  CONCORD  GRAPE.  By  W.  Paddock.  Garden  and  Forest, 
No.  456,  pp.  464-466  ;  also  in  Experiment  Station  Record,  VIII,  290. 

COLOR  EFFECTS  IN  CROSSING  SWEET  AND  FLINT  CORNS.  Bulletin  Illi- 
nois Experiment  Station,  No.  21  ;  also  in  Experiment  Station  Record, 
XIII,  740. 

DETERMINATE  VARIATION  AND  ORGANIC  SELECTION.  By  J.  M.  Baldwin. 
Science,  VI,  770-773. 

THE  DEVELOPMENT  OF  THE  HYBRIDS  BETWEEN  FUNDULUS  HETERO- 
CLITUS  AND  MENIDIA  NOTATA,  WITH  ESPECIAL  REFERENCE  TO  THE 
BEHAVIOR  OF  THE  MATERNAL  AND  PATERNAL  CHROMATIN.  By 
W.  J.  Moenkhaus.  American  Journal  of  Anatomy,  III,  29. 

EFFECT  OF  FERTILIZATION  UPON  FRAGRANCE.  Experiment  Station 
Record,  VIII,  55. 

EFFECT  OF  SPAYING  UPON  THE  QUALITY  OF  MILK.  Experiment  Station 
Record,  XIV,  182. 

ESSAYS  ON  HEREDITY.    By  A.  Weismann.    2  vols. 

EVOLUTION  IN  A  DETERMINATE  LINE.  By  Bashford  Dean.  Biological 
Bulletin,  VII,  105-112. 


2i8  CAUSES  OF  VARIATION 

EVOLUTION  ON  PREDETERMINED  LINES.  By  T.  D.  A.  Cockerell.  Science, 

XIII,  311-312. 
EXPERIMENTAL  STUDY  OF  VARIATION.    By  J.  C.  Ewart.    Report  of  the 

British   Association  for  the  Advancement  of   Science,  LXXI,  666- 

680. 
EXPERIMENTS  IN  CROSSING  CORN  AND  WATERMELONS.    By  F.  C.  Card 

and  G.  E.  Adams.    Experiment  Station  Record,  XIII,  740. 
EXPERIMENTS  UPON  THE  INFLUENCE  OF  THE  SEXUAL  CELLS  UPON  THE 

SOMATIC.    By  G.  W.  Field.    Biological  Bulletin,  II,  346-347. 
HETEROTYPICAL  DIVISION  IN  MATURATION.    By  T.  H.  Bryce.    Report 

of   the  British  Association  for  the  Advancement  of    Science,   1901, 

pp.  685-687. 

HYBRIDIZATION  OF  CORN  AND  WATERMELONS.    By  F.  C.  Card.    Experi- 
ment Station  Record,  XI,  928. 
HYBRIDIZING  MELONS:  EFFECT  IN  SUGAR  CONTENT.   Experiment  Station 

Record,  XVI,  229. 
HYBRIDIZING  ZEBRA  AND  HORSE.    (Experiments  of  Baron  de  Parana  in 

Brazil.)    Experiment  Station  Record,  XI,  972. 
INDIVIDUALITY  OF  CHROMOSOMES.    By  H.  Metcalf.    Proceedings  of  the 

Nebraska  Academy  of  Science,  1901. 
INHERITANCE  IN  PARTHENOGENESIS.    By  Ernest  Warren.    Proceedings 

of  the  Royal  Society,  LXV,  154-158. 
ORGANIC   SELECTION.    By   J.   M.   Baldwin  (Science,   IV,  724-725  ;  V, 

634^-636),  E.  D.  Cope  (Science,  II,  124),  and  H.  F.  Osborn  (Science, 

vi,  583-587). 

ORTHOGENETIC  VARIATION.    By  H.   F.   Gadow,  Cambridge.    Science, 

XXII,  637-640. 
ORTHOGENETIC  VARIATION  IN  CERTAIN  MEXICAN  SPECIES  OF  LIZARDS. 

By  H.  F.  Gadow.  Proceedings  of  the  Royal  Society,  LXXI  I,  109-126. 
PHYSIOLOGICAL  SELECTION.  By  G.  J.  Romanes.  Science,  VII,  606-608. 
PREMATURE  FERTILIZATION  INJURIOUS  TO  FRUIT.  Experiment  Station 

Record,  XIV,  634. 

PROBLEM  OF  DEVELOPMENT.    By  E.  B.  Wilson.    Science,  XXI,  281-293. 
SECONDARY  SEXUAL  CHARACTERS.    (A  study  of  the  effects  of  castration.) 

By  S.  G.  Shattuck  and  C.  G.  Seligmann.    Proceedings  of  the  Royal 

Society,  LXXI  1 1,  49-58. 
SEXUAL  REPRODUCTION  ;   DISTINCTION  FROM  ASEXUAL.    By   Richard 

Hertwig  (translated  by  W.  C.  Curtis).    Science,  XII,  940-946. 
SONG  OF  BIRDS  KEPT  FROM  THEIR  OWN  SPECIES.    By  William  E.  D. 

Scott.    Science,  XIX,  154. 
STERILE  FRUIT  BLOSSOMS.    By  S.  A.  Beach.    New  York  Station  Bulletin, 

CLXIX,  33I-37L 

STERILITY  OF  CATTLE,  CAUSES  OF.    Experiment  Station  Record,  XI,  289. 
TELEGONY.    By  J.  C.  Ewart.    Proceedings  of  the   Royal  Society,  LXV, 

243-251. 


INTERNAL  CAUSES  OF  VARIATION  219 

TELEGONY   (DISPROVED).    By  J.   C.  Ewart.    Popular  Science  Monthly, 

LVII,  126-133- 
TELEGONY  (DISPROVED)  :  ACCOUNT  OF   EWART'S  EXPERIMENT  WITH 

ZEBROIDS.    By  J.  C.  Ewart.    Breeders'  Gazette,  XLI,  1009;  also  in 

Transactions  of  the  Highland  Agricultural  Society,  1901,  pp.  81-134  ; 

and  in  Experiment  Station  Record,  XI,  1077;  XIII,  275  ;  and  XIV, 

76. 
TELEGONY  (DISPROVED)  :  EXPERIMENT  WITH  GUINEA  PIGS.    By  C.  S. 

Minot.    Report  of  the  British  Association  for  the  Advancement  of 

Science,  1906,  p.  606. 
THE  CHROMOSOMES  IN  HEREDITY.    By  W.  S.  Sutton  (1903).    Biological 

Bulletin,  IV. 

THE  GERM  PLASM.    By  A.  Weismann.    i  vol. 
THE  PHYSICAL  BASIS  OF  HEREDITY.    By  K.  H.  Eigenmann.    Popular 

Science  Monthly,  LXI,  32-44. 
THEORY  OF  HEREDITY  AND  TELEGONY.    By  J.  C.  Ewart.    Nature,  LX, 

330-333- 

XENIA,  EXAMPLE  IN  APPLE.    By  L.  H.  Bailey.    Science,  IV,  498-499. 
XENIA,  OR  DOUBLE  FERTILIZATION.    (Review  of  work  of   De  Vries, 

Correns,  and  Webber.)    Experiment  Station  Record,  XII,  421,  717; 

also  XIII,  620. 
XENIA  IN  MAIZE.    By  Hugo  De  Vries.    Experiment  Station  Record,  XI, 

1016. 


CHAPTER  IX 

EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION 

It  was  long  ago  noted,  and  the  most  casual  observer  cannot 
fail  to  discover,  that  individuals  of  the  same  species  vary  greatly 
according  to  their  environment,  —  meaning  by  that  term  all  the 
external  conditions  of  life,  such  as  climate,  food,  friends,  enemies, 
and  all  those  outside  influences,  favorable  or  unfavorable,  among 
which  the  individual  finds  itself  born,  and  with  which  it  must 
live  upon  the  best  terms  possible  if  it  would  live  at  all.  That 
these  external  agencies  exert  a  direct  effect  upon  living  matter 
is  beyond  question,  and  it  remains  to  give  attention  to  the  nature 
and  extent  of  this  influence  as  a  partial  answer  to  the  question 
we  would  solve,  —  the  dependence  of  organized  living  matter 
upon  the  external  world  for  the  nature  and  range  of  its  activities. 
Anything  we  may  learn  upon  this  point  will  be  a  contribution  to 
the  stock  of  knowledge  out  of  which  we  shall  one  day  determine 
all  the  causes  of  variation. 

Without  a  doubt  the  great  bulk  of  variability  is  due  to 
causes  internal  to  the  organism,  mainly  in  the  form  of  inherited 
tendencies.  Pearson,  after  exhaustive  statistical  investigations, 
remarks,  "  The  individual  contains  within  itself,  owing  to  a  bath- 
mic  law  of  growth,  a  variability  which  is  itself  quite  sensible, 
being  80  or  90  per  cent  of  the  variability  of  the  race."  1 

Even  then,  however,  these  internal  influences  are  dependent 
upon  outside  conditions  for  their  opportunity.  A  born  giant 
must  have  food  in  abundance,  but  no  amount  of  food  would 
make  a  giant  out  of  a  dwarf.  Nor  will  it  avail  to  awaken,  late 
in  life,  forces  that  once  might  have  been  active.  Some  dwarfs 
are  therefore  born  and  others  are  produced  by  insufficient  food. 

The  external  conditions  of  life  affect  variability  in  four  dis- 
tinctly different  ways  :  (i)  through  natural  selection,  influencing 

1  Pearson,  Grammar  of  Science,  p.  473. 
220 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION    221 

* 

the  type  ;  (2)  by  affording  or  withholding  the  opportunity  for  the 
proper  development  of  the  characters  born  into  the  individual  and 
therefore  representing  internal  forces ;  (3)  by  exerting,  directly 
upon  the  organism,  a  stimulating  or  a  depressing  effect  upon  its 
normal  activities ;  (4)  in  extreme  cases  by  temporarily  or  per- 
manently modifying  the  character  of  normal  functions. 

The  first  manifestly  affects  the  type  and  the  race  as  a  whole, 
while  the  second,  third,  and  fourth  primarily  affect  the  individual. 
It  is  with  these  latter  that  we  are  now  concerned. 

The  hasty  student  credits  to  external  conditions  all  that  would 
happen  if  these  conditions  were  withdrawn.  This  is  erroneous. 
A  very  large  part  of  all  that  happens  is  due  primarily  to  internal 
causes, because  different  races  are  differently  affected  by  the  same 
conditions.  The  fundamental  cause  of  variability  is  therefore  to 
be  sought  in  the  form  of  inherited  characters,  even  though  these 
are  dependent  upon  external  conditions  for  their  development, 
which  may  themselves  seem  to  be  direct  causes  of  variation. 

It  is  therefore  proper  enough  to  speak  of  external  conditions 
of  life  as  causes  of  variability,  providing  we  know  what  we  mean 
thereby  and  are  careful  to  distinguish  between  their  indirect 
effect,  on  the  one  hand,  in  affording  or  withholding  the  con- 
ditions of  development  in  which  their  influence  is  secondary, 
and  their  direct  influence,  on  the  other  hand,  in  stimulating, 
depressing,  or  altering  the  activities  of  the  organism. 

With  these  distinctions  in  mind  we  may  study  the  effects  of 
outside  conditions  upon  variability  without  danger  of  attributing 
to  them  what  properly  belongs  to  inherited  faculties. 

SECTION  I  —  GENERAL  EFFECT  OF  LOCALITY  UPON  PLANT 
AND  ANIMAL  DEVELOPMENT 

It  is  a  matter  of  common  knowledge  that  the  texture  and 
quality  of  garden  vegetables  depend  very  much  upon  the  con- 
ditions under  which  they  are  grown,  and  that  the  highest  flavor 
of  the  orange,  peach,  pineapple,  and  edible  fruits  generally  is 
found  only  in  specimens  from  certain  favored  localities. 

Thus  cantaloupes  of  extremely  high  quality  developed  first  at 
Rockyford,  Colorado,  and  afterward  in  a  few  other  sections. 


222  CAUSES  OF«  VARIATION 

American  seed  growers  generally  seem  to  have  settled  upon 
Kansas  as  the  spot  most  favorable  to  the  development  of  the 
highest  quality  in  the  watermelon,  and  it  is  accordingly  the 
favorite  seed-producing  locality.  Darwin  tells  us  that  "  the  seed 
of  the  Persian  melon  yields  near  Paris  a  fruit  inferior  to  the 
poorest  market  kinds,  but  at  Bordeaux  yields  delicious  fruit."  : 

European  varieties  of  grapes  failed  so  utterly  in  eastern  North 
America  as  to  necessitate  the  developing  of  varieties  from  the 
native  vine. 

Indian  corn  develops  local  varieties  with  extreme  readiness, 
but  they  seldom  succeed  when  transferred  even  short  distances, 
at  least  until  time  enough  for  acclimatization  has  elapsed.  The 
writer  sent  a  standard  white  Illinois  corn,  ripening  in  about  a  hun- 
dred and  twenty  days  and  capable  of  maximum  yields  (seventy-five 
bushels  per  acre),  to  be  grown  in  Michigan,  Wisconsin,  Maine,  and 
Mississippi.2  In  Maine  it  failed  to  ripen,  but  at  all  other  points 
it  ripened  in  about  a  hundred  days,  producing  small,  inferior 
ears,  altogether  worthless  as  a  commercial  crop.  That  it  should 
hurry  through  its  period  of  growth  at  the  north  was  not  surpris- 
ing, but  that  it  should  do  the  same  at  the  south,  where  it  had 
even  more  time  at  its  disposal  than  at  home,  is  unaccountable. 

Wheat,  on  the  other  hand,  is  a  cosmopolitan  crop,  and  while 
varieties  succeed  better  in  some  localities  than  in  others,  yet  a 
new  variety  seldom  fails,  and  sometimes  succeeds  even  better 
than  in  the  locality  whence  it  came.  However,  it  is  altogether 
likely  that  no  known  wheat-growing  region  equals  England  in 
natural  advantages  for  maximum  yields.  This  is  supposed  to  be 
due  to  the  humid  atmosphere  and  cloudy  skies  during  the  later 
stages  of  growth,  in  sharp  contrast  to  the  bright  skies  and  hot 
dry  air  of  America  at  this  season.  If  this  be  the  true  partial 
explanation  of  the  occasional  phenomenal  and  always  high  yields 
in  Great  Britain,3  we  may  hope  for  equal  results  some  day  in  the 
similar  climate  of  Oregon. 

1  Darwin,  Animals  and  Plants,  II,  264. 

2  Wisconsin,  200  miles  north;  Michigan,  200  miles  north  and  100  miles  east; 
Maine,  300  miles  north  and  900  miles  east ;  Mississippi,  450  miles  south. 

8  The  average  wheat  yield  of  the  United  States  is  between  12  and  13  bushels 
per  acre,  while  that  of  Great  Britain  is  almost  exactly  30,  and  a  maximum  of  90 
bushels  has  been  reported. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION    223 

The  experiments  of  Bonnier  upon  this  general  subject  are 
classic.1  He  divided  dandelion,  helianthus,  and  many  other 
plants  growing  in  the  valley,  and  planted  one  half  of  each  indi- 
vidual plant  on  the  mountain  at  an  elevation  of  2300  to  2400 
meters,  leaving  the  other  half  in  the  valley  (how  much  below 
he  does  not  say).  As  the  division  was  made  by  a  vertical  cut 
through  the  fleshy  root,  the  two  halves  must  have  been  practi- 
cally alike. 

He  found  that  the  portions  on  the  mountain  developed  plants 
much  smaller  than  those  in  the  valleys.  The  difference  was 
mainly  in  the  length  of  the  internodes,  not  in  their  number. 
The  leaves  of  the  dandelion  were  less  than  one  fifth  as  long 
when  drawn  to  scale,  and  the  flower  stalks  were  not  one  tenth  as 
long.  The  mountain  plants  in  general  developed  higher  colors. 

Darwin  tells  us  that  the  medicinal  qualities  of  digitalis  are 
"  easily  affected  by  culture,"  and  that  "  the  wood  of  the  Amer- 
ican locust  tree  (Robinia)  when  grown  in  England  is  nearly 
worthless,  as  is  that  of  the  oak  tree  when  grown  at  the  Cape  of 
Good  Hope."  2  The  same  author  quotes  Sir  J.  E.  Tennent  as 
saying  that  "in  the  Botanic  Gardens  of  Ceylon  the  apple  tree 
'  sends  out  numerous  runners  underground,  which  continually 
rise  into  small  stems,  and  form  a  growth  around  the  parent 
tree.'  "  3  If  this  be  true,  its  naturally  slight  tendency  to  sprout 
has  in  this  locality  developed  into  a  pronounced  habit. 

Sheep,  especially  the  merinos,  are  cosmopolitan,  and  yet  they 
succeed  nowhere  else  as  in  New  Zealand.  On  the  other  hand, 
according  to  Darwin  they  seem  not  to  succeed  in  the  West 
Indies  or  on  the  west  coast  of  Africa,  where  "  the  wool  disap- 
pears from  the  whole  body  except  over  the  loins."4  The  writer 
has  seen  the  same  thing  in  Brazil,  except  that  the  best-clothed 
portion  of  the  body  was  the  back  of  the  neck,  the  same  spot  on 
which  the  vicuna  bears  its  fur. 

The  statement  is  frequently  made  that  fat-tailed  sheep  rapidly 
lose  this  character  when  removed  from  their  native  saline  pas- 
tures, but  the  assertion  needs  confirmation,  for  the  writer  has 

1  C.  Bonnier,  Recherches  experimentales  sur  1'adaptation  des  plantes  au  climat 
alpin.    Annales  des  sciences  naturelles,  7e  Serie,  Tome  XX,  1895. 

2  Darwin,  Animals  and  Plants,  II,  264.          3  Ibid.  p.  266.          *  Ibid.  I,  102. 


224 


CAUSES  OF  VARIATION 


seen  a  respectable  development  of  fat  when  the  sheep  were  kept 
under  ordinary  conditions. 

One  of  the  most  remarkable  and  seemingly  best  authenticated 
instances  of  the  evil  influence  of  locality  upon  character  devel- 
opment is  the  almost  uniform  failure  to  maintain  the  quality  of 
certain  English  breeds  of  dogs  when  bred  in  India.  We  are 
indebted  again  to  Darwin 1  for  the  remarkable  statement  that  in 
that  country  the  bulldog  rapidly  loses  his  ferocity,  and  of  all 
dogs  the  hounds  decline  most  rapidly. 

Instances  might  be  multiplied  indefinitely,  but  two  things 
must  be  borne  in  mind  by  the  student  when  dealing  with  this 
class  of  facts  :  first,  there  is  the  greatest  opportunity  for  error 
or  exaggeration  from  inexact  observation  and  report ;  second, 
the  plant  or  animal  is  exposed  to  a  multitude  of  new  conditions 
when  transplanted  to  a  new  locality,  only  a  portion  of  which  are 
inherent  in  the  conditions  of  life.  Commonly  the  breeders  or 
attendants  are  not  familiar  with  the  new  form  and  do  not  afford 
proper  conditions,  as  in  not  giving  suitable  food  to  animals  or 
in  failing  to  afford  sufficient  room  to  large-growing  varieties 
of  plants.2 

After  making  due  allowance,  however,  for  all  these  considera- 
tions, the  fact  remains  that  the  conditions  of  life  evidently  do 
exert  a  strongly  modifying  influence  upon  development. 

Locality  a  comprehensive  term.  There  is  little  use  in  attempt- 
ing to  determine  the  exact  influence  of  each  separate  locality. 
The  term  is  an  exceedingly  comprehensive  one,  including  many 
things, — climate,  by  which  we  mean  not  only  temperature, 
moisture,  and  light,  but  their  comparative  proportions  in  that 
particular  spot ;  season,  by  which  we  mean  the  succession  of 
climatic  conditions ;  food  (both  as  to  quantity  and  quality),  on 
which  the  creature  absolutely  depends,  not  only  for  life  but  also 
for  growth  ;  habits  of  life,  radical  changes  in  which  may  be  forced 
upon  the  animal  by  its  habitat. 

This  is  all  too  complex  for  profitable  study  anji  discussion. 
We  must  separate  locality  into  its  elements  and  determine,  if  we 

1  Darwin,  Animals  and  Plants,  I,  39. 

2  It  will  be  noted  in  this  connection  that  most  of  the  instances  cited  are  those 
of  deterioration. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION    225 

can,  the  particular  modifying  influence  of  each  of  the  conditions 
of  life  with  which  animals  and  plants  are  surrounded.  In  this  way 
we  may  get  important  information  upon  this  most  difficult  and 
unsatisfactory  subject.  Accordingly  we  undertake  to  ascertain 
the  effects  due  specifically  to  food,  temperature,  light,  etc.,  —  the 
elements  that,  taken  together,  constitute  the  conditions  of  life. 

SECTION  II— THE  INFLUENCE  OF  FOOD  UPON 
VARIABILITY 

The  best  evidence  goes  to  show  that  food  affects  develop- 
ment both  quantitatively  and  qualitatively.  It  is  expedient  to 
consider  the  two  separately. 

Quantitative  effects  of  food.  In  general,  as  every  stockman 
knows,  full  feed  means  increased  size,  provided  always  there 
has  been  no  check  during  development.  This  is  not  only  the 
experience  in  the  yards  everywhere,  but  the  world  over  the 
largest  animals  are  found  on  the  best  feeding  grounds.  Doubt- 
less other  external  influences  affect  size,  but  certainly  no  other 
equals  the  food  supply,  and  if  maximum  development  is  expected 
food  must  not  be  withheld,  especially  during  the  early  stages  of 
growth.  No  amount  of  later  feeding,  after  the  individual  has 
accustomed  itself  to  a  reduced  supply,  can  make  amends  for 
early  shortage.  This  is  itself  a  deviation  which  easily  becomes 
permanent  and  follows  the  individual  through  life. 

Development,  however,  bears  no  direct  ratio  to  food  con- 
sumed ;  that  is  to  say,  the  greater  portion  of  all  food  is  consumed 
in  supporting  the  vital  processes,  altogether  without  reference 
to  increase  of  weight  or  to  labor  performed.  Under  the  best  of 
feeding  we  rarely  recover  10  per  cent  of  the  food  consumed  in 
the  form  of  growth  or  increase  of  weight,  and  seldom  realize  as 
much  as  one  sixth  in  the  form  of  labor  or  other  output  of  the 
body.  The  great  mass  of  the  food  is  either  not  digested  at  all 
or  goes  to  support  the  internal  activities  of  the  body,  or  else  is 
digested  and  passed  out  of  the  body  without  serving  any  useful 
purpose  whatever. 

It  is  a  significant  fact  that  stunted  animals  (and  plants  as  well) 
seldom  recover  from  the  evil  effects  of  arrested  development, 


226  CAUSES  OF  VARIATION 

and  that  under-development  due  to  insufficient  food  is  quite 
distinct  from  dwarfing,  especially  among  animals,  in  that  the 
body  does  not  develop  proportionately.  In  underfed  calves,  for 
example,  the  head  outgrows  the  rest  of  the  body,  the  legs  are 
long,  and  the  joints  are  large. 

In  general,  full  feed  means  not  only  increased  size  but  early 
maturity  as  well,  which  is  of  even  greater  consequence.  Because 
of  the  large  proportion  of  food  never  recovered  in  gain,  it  is 
manifest  that  any  shortening  in  the  period  of  development  re- 
sults not  only  in  improved  quality  but  also  in  the  saving  of  feed  ; 
in  other  words,  early  gains  are  economical  gains  and  they  tend 
to  higher  quality. 

Effect  upon  fertility.  The  amount  and  character  of  food  often 
exert  profound  physiological  influences.  For  example,  the  fer- 
tility of  the  female  honeybee  is  mainly  due  to  food,  the  sterile 
workers  and  the  fertile  queens  developing  from  the  same  eggs. 
If,  even  after  the  worker  eggs  are  hatched  and  the  larvae  well 
developed,  they  be  taken  from  the  worker  cells,  put  into  queen 
cells,  and  fed  "  queen's  food,"  they  will  develop  into  queens,  — 
a  fact  often  taken  advantage  of  by  the  bees  themselves  when  by 
accident  all  the  prospective  queens  have  been  lost.  Here  fertility 
is  largely  a  matter  of  food,  although  an  occasional  worker  is 
known  to  produce  eggs.  This  general  difference  between  worker 
and  queen  must  therefore  be  regarded  as  one  of  development 
dependent  mainly  on  the  food  supply. 

Speaking  generally,  excessive  food  supply  leads  to  infertility 
among  both  plants  and  animals.  The  former  vegetate  luxuri- 
ously, but  they  do  not  blossom  and  fruit  so  abundantly  as  under 
a  full  but  moderate  supply  of  plant  food. 

Whether  the  effect  in  question  is  due  to  overfeeding  or  to 
some  one  or  two  elements  in  particular  is  not  well  established. 
Enough  is  known,  however,  to  justify  the  assertion  that  extreme 
proportions  of  nitrogen  produce  luxuriance  in  stem  and  leaf  at 
the  expense  of  flower  and  fruit,  but  there  is  exceeding  doubt 
whether  this  effect  would  follow  a  well-balanced  food  supply 
with  plenty  of  phosphorus. 

Excessive  feeding  of  animals,  especially  females,  tends  to  fatty 
degeneration  of  the  essential  sexual  organs,  and  consequently  to 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION    227 

sterility,  and  this  result  is  hastened  if  the  food  contains  unusual 
proportions  of  carbohydrates,  especially  sugar. 

Effect  of  feed  upon  variability.  It  is  a  common  belief  that 
plants  and  animals  are  more  variable  when  well  fed  than  other- 
wise. Doubtless  this  is  true,  so  far  at  least  as  appearances  go, 
for  only  under  such  favorable  conditions  are  all  the  faculties 
that  are  born  into  the  exceptional  individual  able  to  develop  and 
become  visible.  When  a  race  is  living  under  mediocre  conditions 
there  is  a  dead  level  in  development.  The  mediocre  individuals 
have  relatively  the  best  chance,  and  few,  will  rise  above  the  con- 
dition of  mediocrity. 

Whether  full  feed  is  a  direct  stimulant  to  variability  or  only 
brings  potential  differences  to  the  surface  is  therefore  an  open 
question.  The  procedure  indicated  is,  however,  in  either  case  the 
same ;  namely,  to  provide  maximum  conditions  if  the  breeder 
expects  to  realize  the  utmost  from  his  best  individuals  or  hopes 
ever  to  find  variations  worth  preserving. 

Herein  lies  the  fact  that  well-bred  animals  often  require  more 
feed  than  their  scrub  relatives.  It  was  upon  that  point  that  they 
departed  from  their  kind  —  not  that  they  contracted  to  exist  on 
less  feed,  but  that  they  were  able  to  handle  more  feed  and  put 
it  to  good  use.  If  the  purpose  of  the  breeder  were  to  develop 
races  with  a  minimum  maintenance  ration,  it  could  be  done;  but 
we  keep  domestic  animals  not  for  their  society  but  for  what  they 
can  do,  —  for  what  they  can  manufacture  out  of  corn,  oats,  and 
hay.  We  improve  crops,  not  to  see  upon  how  poor  land  they  may 
live,  but  rather  to  increase  their  ability  to  construct  valuable  food 
materials  from  the  mineral  elements  of  the  soil  and  the  inorganic 
constituents  of  the  atmosphere.  Not  minimum  of  consumption 
but  economic  consumption  is  therefore  the  virtue  sought. 

Evil  effects  of  overfeeding.  The  plant  will  seldom  suffer  from 
abundance  of  food,  although  it  is  not  impossible.  Excess  of 
nitrogen  causes  rank  growth  of  stem,  but  phosphorus  is  needed 
for  seed.  Something  akin  to  a  balanced  ration  is  doubtless  best 
for  plant  as  well  as  animal,  yet  the  former  has  more  of  selective 
ability  than  the  latter. 

The  animal  is  easily  overfed,  and  if  so  the  injury  is  likely  to 
be  permanent.  It  results  (i)  in  disorders  of  the  digestive  tract ; 


228  CAUSES  OF  VARIATION 

(2)  in  disorders  of  the  excretory  organs  ;  (3)  in  excessive  fat ; 
(4)  in  sterility,  especially  in  females,  through  fatty  degeneration 
of  the  essential  sexual  organs. 

Qualitative  effects  from  the  nature  of  the  food.  The  color 
of  plants  and  flowers,  and  even  of  animals,  is  said  often  to  be 
directly  influenced  by  their  food,  but  it  is  exceedingly  difficult 
always  to  separate  fact  from  tradition  in  this  particular  field, 
because  the  average  person  has  an  exaggerated  conception  of 
the  influence  of  food  upon  the  constitution  of  the  organism, 
often  believing  that  a  meat  diet,  for  example,  inclines  to  ferocity 
and  uncontrollable  temper  generally.  Darwin l  mentions  the 
practice  of  feeding  hemp  seed  to  bullfinches  to  darken  their 
color ;  the  fat  of  a  certain  fish  to  parrots,  causing  them  to 
"become  beautifully  variegated  with  red  and  yellow  feathers." 
He  also  states  that  the  shells  of  mollusks  are  largely  influenced 
by  the  amount  of  lime  in  the  water  in  which  they  grow,  and 
Beal  succeeded  in  growing  blue  hydrangeas  from  pink  stock  by 
occasional  application  of  alum  water  to  the  roots. 

That  the  flavor  of  milk  and  eggs  is  largely  dependent  upon 
food  has  long  been  known,  as  has  the  specific  effect  of  certain 
foods  upon  the  texture  and  flavor  of  meat.  Mumford  found  at 
Illinois  that  the  fat  of  pork  fed  upon  large  amounts  of  cotton 
seed  proved,  on  chemical  examination,  to  contain  a  proportion 
of  true  cotton-seed  oil,  showing  that  a  portion  at  least  of  the 
food  had  been  carried  over  and  stored  unchanged  in  the  tissues. 

That  this  is  the  exception,  or  perhaps  more  correctly  the 
lesser  result,  is  proved  by  the  fact  that  in  general  the  identity  of 
the  food  is  lost  in  the  nature  of  the  organism,  showing  that  the 
organism  and  not  its  food  dominates  results.  The  same  meat 
becomes  dog  or  man  indifferently,  indicating  that  food  com- 
pounds are  not  as  a  rule  carried  over  but  rather  "  suffer  profound 
disruption,"  being  reduced,  if  not  to  their  elements, at  least  to  com- 
paratively simple  compounds,  the  energy  set  free  in  the  disrup- 
tion being  "  utilized  in  the  subsequent  work  of  construction."  2 

The  higher  organisms  are  comparatively  independent  of  their 
food  so  far  as  qualitative  changes  are  concerned.  They  seem 

1  Darwin,  Animals  and  Plants,  II  (second  edition),  269-270. 

2  Encyclopaedia  Britannica,  XIX  (1885),  article  "Physiology,"  21. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION    229 

able  to  extract  the  materials  for  their  activities  often  from  the 
most  forbidding  sources  and  under  the  most  discouraging  cir- 
cumstances. Indeed,  many  forms  of  animal  activity  are  depend-, 
ent  for  support  not  so  much  upon  the  materials  of  the  food  as 
upon  its  energy.  This  applies  more  especially  to  mature  animals 
and  their  functional  activity,  but  we  also  remember  that  in  the 
business  of  body  building,  materials  are  required  in  large  excess 
of  the  actual  amounts  retained  in  the  body. 

Lower  forms  of  life,  however,  seem  often  greatly  dependent 
upon  their  culture  medium.  Thus  many  bacteria  grow  quite  dif- 
ferently upon  the  potato  and  in  agar  or  in  beef  broth,  and  a  germ 
disease  often  presents  in  one  species  symptoms  substantially 
different  from  those  it  presents  in  another. 

The  animal  and  the  plant  (among  the  higher  forms)  are 
nourished  upon  fundamentally  distinct  plans.  Both  require 
that  food  be  in  the  soluble  form  before  it  can  be  useful,  and 
each  makes  use  only  of  such  available  materials  as  it  may  need. 
But  the  animal  is  provided  with  an  elaborate  excretory  system 
by  which  it  frees  itself  of  all  residues,  both  of  undigested  food  and 
of  broken-down  tissues,  and  also  of  digested  food  in  excess  of 
requirements.  By  this  means  the  animal  is  promptly  freed  from 
all  redundant  food  material. 

It  is  not  so  with  the  plant.  It  takes  in  food  by  absorption  at 
its  roots,  and  the  water  carries  with  it  anything  and  everything 
that  may  happen  to  be  dissolved.  If  nothing  poisonous  enters, 
the  plant  will  live,  but  it  will  be  loaded  with  residues,  because  it 
has  no  excretory  system.  The  water  passes  off  by  evaporation 
at  the  leaf  surface,  leaving  at  that  point  large  quantities  of  what- 
ever was  dissolved  in  the  juices  of  the  plant.  We  are  not  sur- 
prised, therefore,  that  vegetation  of  the  same  species  differs 
very  widely  in  composition  in  different  localities,  especially  with 
respect  to  mineral  content,  depending  upon  the  character  of  the 
soil  in  which  it  was  grown.  This  difference  may  be,  as  in  the 
case  just  cited,  quite  independent  of  vital  processes,  and  due  to 
nothing  more  than  accident. 

Plants,  and  the  simpler  organisms  generally,  are  of  necessity 
far  more  dependent  upon  their  environment,  and  especially  their 
food,  than  are  the  higher  animals,  that  have  to  a  large  extent 


230 


CAUSES  OF  VARIATION 


freed  themselves  from  the  bondage  due  to  the  accident  of  birth- 
place, being  able  to  move  about  and  therefore  to  establish  in  the 
.widest  sense  an  independent  existence. 

Notwithstanding  all  this,  and  after  making  allowance  for  the 
grosser  influences  over  lower  organisms,  the  fact  yet  remains 
that,  to  a  slight  extent,  and  to  a  slight  extent  only,  the  animal 
is  influenced  by  the  character  of  his  food.  That  this  influence  is 
larger  upon  the  products  of  the  body  than  upon  the  body  itself 
is  certain  ;  and  upon  the  subtler  qualities,  like  flavor,  rather  than 
the  more  essentially  biological  characters  such  as  structure. 

SECTION   III  — THE   EFFECT   OF   MOISTURE   UPON 
DEVELOPMENT 

Animals  as  a  rule  are  quite  independent  of  moisture,  providing 
their  direct  needs  for  water  are  satisfied  in  the  way  of  body 
consumption  in  addition  to  that  needed  to  reduce  the  effects  of 
internal  heat  by  evaporation.1 

Plants  on  the  other  hand  do  not  have  the  circulatory  system  of 
animals,  and  they  depend  upon  water,  taken  in  by  the  roots  and 
evaporated  by  the  leaves,  to  actually  carry  food  to  all  parts  of  the 
structure.  Their  need  for  water  is  therefore  far  above  the  amounts 
necessary  for  actual  composition.  For  example,  it  requires  the 
evaporation  of  something  like  the  equivalent  of  eight  inches  of 
standing  water  over  the  entire  field  to  mature  an  average  corn  crop. 

1  It  is  often  erroneously  taught  that  animals  consume  carbonaceous  foods  to 
sustain  the  body  temperature,  while  the  truth  is  that  all  food  actually  utilized  is 
broken  down  and  its  energy  set  free.  This  energy  is  disposed  of  in  three  ways : 
first,  to  a  slight  extent  in  effecting  the  recombination  of  the  elements  of  the  food 
into  the  exceedingly  complex  protoplasm  of  the  body  or  its  products ;  second,  by 
the  body  or  some  of  its  parts  in  the  form  of  internal  or  of  external  work  ;  or,  third, 
it  is  radiated  in  the  form  of  heat  of  low  intensity.  In  this  way  the  body  is  a  factory 
that  is  constantly  producing  heat,  which  must  be  disposed  of  or  the  structure  will  be 
destroyed.  There  are  but  two  ways  of  doing  this,  —  by  radiation  and  by  evapora- 
tion. The  body  is  thus  constantly  producing  and  is  as  constantly  losing  heat.  Its 
actual  temperature  is  certain  to  be  something  above  that  of  the  surrounding'medium, 
—  how  much  will  depend  upon  the  relation  between  the  rapidity  of  production 
and  the  facilities  for  radiation  and  evaporation.  The  body  temperature  is  thus  a 
kind  of  algebraic  sum,  and  it  depends  upon  a  great  variety  of  conditions.  Small 
animals  radiate  rapidly,  large  ones  less  rapidly,  for  radiation  is  a  surface  action, 
and  their  surface  is  less  in  proportion  to  the  bulk.  Hogs  radiate  slowly,  because 
of  their  blanket  of  fat.  They  do  not  sweat,  and  thus  are  easily  overheated. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION 


231 


Water,  or  the  lack  of  it,  is  therefore  in  many  countries  and  in 
many  seasons  the  limiting  element ;  that  is  to  say,  the  yield  is 
limited  not  by  the  available  fertility  or  the  ability  of  the  crop  but 
by  the  moisture  present. 

In  excessively  wet  seasons  crops  are  notoriously  "  soft,"  that  is, 
lacking  in  substance.  Just  what  the  difference  is  has  not  been 
well  established,  but  size  has  been  attained  at  the  expense  of 
quality.  There  is  good  reason  to  assume  that  it  is  the  result  of 
abundance  of  water,  leading  to  full  cellular  development,  but 
deficiency  of  evaporation  and  transfusion  of  food  due  to  cloudy 
skies,  resulting  in  a  lack  of  actual  dry  matter. 

Effect  of  moisture  in  the  atmosphere.  It  is  said  that  moist 
atmospheres  produce  fineness  of  hair  or  fur  in  animals  and  deli- 
cate foliage  in  plants,  and  that  a  dry  atmosphere  inclines  to  a 
harsh,  dry  coat  and  to  spiny  growth  in  plants.  Under  natural 
conditions,  however,  moisture  is  often  associated  with  coolness  and 
shade,  and  dryness  with  great  heat  and  intense  light.  Certain  it 
is  that  fur-bearing  animals  are  found  in  cool  climates  and  that 
vegetation  is  delicate  in  the  temperate  region  but  harsh,  dry, 
and  spiny  in  the  arid  sections.  These  facts  are  well  known  and 
universally  recognized,  but  how  much  is  due  to  moisture  alone 
cannot  well  be  determined  in  nature. 

Resorting  to  direct  experiment,  however,  we  find  that  the  same 
plant  may  be  grown  with  or  without  spines  according  to  the 
degree  of  moisture  in  the  surrounding  atmosphere.  Spines  are 
undeveloped  leaves,  as  thorns  are  abortive  stems,  and  anything 
that  checks  growth  tends  to  their  production.  That  this  is  mainly 
the  result  of  a  dry  atmosphere,  however,  is  easily  shown  in  the 
laboratory. 

"  Lothelier  has  made  numerous  observations  in  which  individ- 
uals of  the  same  species  were  placed  side  by  side,  some  exposed 
freely  to  the  air  and  others  kept  moist  under  a  glass  shade." 
Under  conditions  such  as  this  "  Berberis  vulgaris  bore  non- 
spinescent  leaves  in  a  moist  atmosphere,  but  spines  alone  in  a 
perfectly  dry  one.  Again,  the  shoots  which  in  Lycium  barbarum, 
Ulex  Europcens,  etc.,  would  normally  have  formed  thorns,  by 
arrested  development  and  sclerosis  (hardening),  in  a  very  damp 
atmosphere  continued  to  grow,  and  elongated  into  leafy  branches." 


CAUSES  OF  VARIATION 

Microscopical  examination  showed  that  in  the  dry-air  specimens 
"  the  palisade  cells  were  well  developed  and  there  was  a  special 
consolidation  of  fibrous  tissues."  l  The  same  author  continues  : 

Again,  the  common  water  reed  Phragmites  communis,  when  growing  in 
the  unirri gated  areas  of  the  Nile  valley,  forms  a  stunted  growth  with  very 
short  and  sharp-pointed  leaves.  Close  to  the  Nile,  however,  ...  it  grows 
nine  or  ten  feet  high,  with  long  leaves  almost  exactly  like  the  plants  in 
English  rivers. 

All  observations  go  to  show  that  the  number  of  vessels  in  the 
fibre-vascular  system  is  greater  in  the  aerial  than  in  the  aquatic 
forms  of  the  same  species,2  and  the  evidence  in  general  seems 
conclusive  that  the  notorious  abundance  of  spines  in  tropical 
vegetation  is  due  primarily  to  a  dry  atmosphere,  assisted  to 
some  extent,  no  doubt,  by  the  retarding  effect  of  intense  light 
upon  growth. 

A  significant  fact  in  this  connection,  possibly  attributable  to 
the  scarcity  of  water,  possibly  to  the  lack  of  heat,  is  the  well-known 
phenomenon  that  plant  lice,  producing  females  only  during  the 
summer,  begin  with  approaching  autumn  to  produce  males,  and 
that  under  the  perpetual  heat  of  the  greenhouse  the  insects  ob- 
serve summer  habits  indefinitely  tmless  tJie  plants  on  which  they 
are  feeding  are  allowed  to  become  dry. 

As  is  well  known,  seeds  may  be  kept  for  long  periods  if 
thoroughly  dried.  In  this  case  the  vital  activities  are  reduced  to 
a  minimum,  but  probably  not  entirely  suspended,  because  seeds 
will  not  last  indefinitely.  Certain  lower  forms  of  plant  and  ani- 
mal life  have  a  marked  power  of  apparently  suspending  life 
through  desiccation  and  resuming  its  activities  again  with  suffi- 
cient moisture.3 

The  actual  influence  of  water  upon  development  is  not  yet 
well  understood,  except  that  it  is  one  of  the  absolute  conditions 
of  life,  and,  being  a  fluctuating  element,  often  limits  development. 

The  student  should  fully  appreciate  the  bearing  of  all  this  upon 
the  matter  in  hand  :  The  degree  of  development  of  an  individual 
at  maturity  is  not  a  complete  index  to  his  inherited  characters. 

1  Vernon,  Variation  in  Animals  and  Plants,  p.  264 ;  see  also  Henslow,  Origin 
of  Plant  Structures,  p.  40.  2  Vernon,  Variation  in  Animals  and  Plants,  p.  265. 

3  C.  B.  Davenport,  Experimental  Morphology,  Part  I,  pp.  59-65. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION 


233 


It  is  both  something  less  and  something  more.  It  is  less  by  so 
much  as  the  individual  has  failed  to  develop  because  of  unfavor- 
able external  conditions  ;  it  is  more  by  whatever  development  is 
due  to  the  direct  influence  of  external  conditions. 

This  is  the  principal  reason  why  breeders  have  difficulty  in 
knowing  how  much  to  credit  to  inheritance,  and  it  is  on  this 
account  that  more  knowledge  is  needed  of  the  nature  and  extent 
of  the  development  due  directly  to  external  causes,  and  therefore 
independent  of  inheritance.  After  all,  however,  it  will  be  found 
that  the  total  development  from  all  causes  is  well  within  hereditary 
limits  except,  perhaps,  in  rare  cases  where  the  normal  functions 
may  have  been  altered  by  unusual  conditions. 

SECTION  IV  —  EFFECT  OF  CONTACT  UPON  PROTOPLASMIC 

ACTIVITY  * 

Unstable  chemical  compounds  are  exceedingly  sensitive  to 
mechanical  contact  either  from  solid  bodies  or  from  liquids  or 
gases  in  rapid  motion.  Davenport  says  : 2 

Mechanical  disturbance  can  induce  in  certain  lifeless  compounds  violent 
chemical  changes.  Compounds  which  are  so  affected  are  preeminently 
unstable.  This  instability,  however,  varies  greatly  in  degree.  In  some 
cases  the  blow  of  a  hammer  is  required  to  upset  the  molecules,  the  result 
being  often  a  violent  explosion.  In  other  cases  (e.g.  chloride  or  iodide  of 
nitrogen  3)  the  slightest  touch  of  a  feather  suffices  to  produce  an  explosion. 
Now,  most  of  the  substances  which  explode  upon  impact  [altering  their 
chemical  arrangement  and  properties]  .  .  .  are  organic  compounds,  — 
fulminate,  nitroglycerin,  gun  cotton,  and  picric-acid  derivatives,  —  and 
therefore  it  is  not  surprising  that  we  find  the  notoriously  unstable  proto- 
plasm violently  affected  by  contact. 

"  Of  special  interest  in  this  connection "  is  the  fact  that 
"periodic  disturbances  produce  very  important  molecular  changes 
in  [certain]  chemical  compounds.  Certain  substances  have  a 

1  C.  B.  Davenport,  Experimental  Morphology,  Part  I,  pp.  97-110,  and  Part  II, 
PP-  370-388,  from  which  most  of  the  data  on  this  subject  are  taken.    N.  B.  Con- 
tact agents  are  technically  known  as  molar  agents. 

2  Ibid.  Part  I,  pp.  97-98. 

3  When  chemical  terms  of  this  kind  are  used  outside  of  quotations  the  new 
form  will  be  used,  as  nitrogen  chlorid,  omitting  the  e. 


234  CAUSES  OF  VARIATION 

specific  rate  of  vibration,  so  that  when  this  is  reproduced  by  a 
vibrating  cord  or  plate,  explosion  of  the  substance  may  occur, 
lodid  of  nitrogen  is  one  of  these  substances  which  is  exploded 
by  a  high  note." :  Living  protoplasm  is  no  exception  to  the 
general  rule  that  specially  unstable  compounds  are  sensitive  to 
contact. 

Effect  of  contact  upon  the  metabolism  of  protoplasm.2  It  is  a 
well-known  fact  that  phosphorescence  is  increased  by  mechanical 
irritation.  So  true  is  this  that  the  water  thrown  from  the  pro- 
peller wheels  of  a  steamer  in  tropical  regions  looks  like  liquid 
fire,  and  a  brisk  breeze  moving  over  the  surface  suggests  at  a 
distance  the  white  foam  of  the  surf. 

Contact  also  exerts  a  strongly  stimulating  influence  upon  secre- 
tions, not  only  with  lower  organisms  which  seek  attachments,  and 
the  glands  of  insectivorous  plants,  but  with  higher  animals  as  well.3 

Effect  of  contact  upon  movement.  The  first  effect  of  mechanical 
disturbance  in  protoplasm  is  to  check  all  movement.  Minute  or- 
ganisms, tradescantia  hairs,  etc.,  cease  their  protoplasmic  motion 
by  the  irritation  of  mounting  under  the  cover  glass.  In  higher 
plants  a  sudden  jar  causes  cessation  of  movement  and  often  a 
retreat  of  the  protoplasm  to  one  side  of  the  cell  so  characteristic 
as  to  be  spoken  of  as  "  fright." 

If  an  amoeba  with  pseudopodia  out  is  touched  or  irritated,  it 
immediately  assumes  the  spherical  form,  and  in  general  the  effect 
of  contact  is  to  cause  protoplasm  to  cease  motion  and  assume 
approximately  the  spherical  form,  or,  in  other  words,  to  occupy 
the  least  space  possible.  But  this  is  to  all  intents  and  purposes 
contraction,  and  the  general  principle  may  be  laid  down  that  ex- 
ternal contact  causes  contraction,  especially  noticeable  in  muscle, 
which  is  par  excellence  the  contractile  tissue. 

This  contraction  most  commonly,  and  of  necessity,  operates 
at  first  to  draw  the  organism  away  from  the  irritating  body 
(negative  thigmotaxis),  but  if  the  body  be  long  or  large,  so  that 
locomotion  continues,  then  the  side  next  the  foreign  body  will 

1  This  suggests,  as  the  author  observes,  the  phenomena  of  hearing. 

2  C.  B.  Davenport,  Experimental  Morphology,  Part  I,  pp.  98-99. 

8  As  is  well  known,  the  heifer  that  has  never  produced  a  calf  may  be  made  to 
give  milk  merely  by  persistent  manipulation  of  the  udder. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION    235 

be  shortened  and  the  organism  will  move  in  a  curve  that  will 
speedily  bring  it  into  actual  contact.  It  is  noticeable,  too,  that 
real  contact,  being  once  established,  is  broken  with  difficulty. 
Many  lower  animals,  as  in  aquaria,  coming  in  contact  with  a  plain 
surface,  move  along  that  surface  until  they  reach  a  point  where 
side  and  bottom  or  where  two  sides  join,  and  where  they  can 
place  their  bodies  in  contact  with  two  surfaces.  They  are  likely 
now  to  move  along  the  groove  formed  by  the  two  surfaces  until 
a  corner  is  reached  where  contact  on  three  sides  is  possible. 
Here,  if  anywhere,  the  organism  will  come  to  rest.  It  is  only 
that  it  is  "  more  comfortable  "  ;  that  it  moved  under  the  molar 
impulse  until  it  reached  a  point  where  further  movement  and 
more  complete  contact  were  alike  impossible.  Even  higher 
animals  come  to  the  highest  state  of  rest  when  in  contact  with 
foreign  bodies  on  as  many  sides  as  possible. 

Effect  of  contact  upon  direction  of  movement, —  thigmotaxis, 
or  stereotropism.1  It  is  a  well-known  fact  that  roots  growing  in 
running  water  grow  upstream,  not  downstream,  and  that  many 
fish  at  the  breeding  season  are  possessed  of  an  irresistible  im- 
pulse to  move  against  the  current  (rheotaxis).2  They  therefore 
ascend  the  strongest  currents,  leap  waterfalls,  and  surmount 
every  possible  obstacle  in  upstream  movements,  —  a  passion 
which  ultimately  carries  them  to  their  breeding  grounds  in  shal- 
low water.  It  is  at  these  times  that  salmon  pile  themselves  up 
even  above  the  water  level  and  that  they  will  follow  any  decoy 
that  leads  against  the  current,  even  into  hopeless  traps. 

Thus  may  external  agents  exert  a  strongly  modifying  influ- 
ence upon  such  essential  activities  of  living  matter  as  the 
contractility  of  protoplasm,  resulting  in  definitely  directed  move- 
ments through  their  control  of  muscular  contraction.  As  we 
shall  see,  contact  is  not  the  only  influence  capable  of  stimulat- 
ing contractility  of  protoplasm  and  controlling  the  direction  of 
movement ;  on  the  other  hand,  muscular  tissue  is  exposed  to 
the  exciting  influence  of  a  great  variety  of  circumstances  both 
internal  and  external  to  the  organism,  any  one  of  which  will 
induce  the  characteristic  reaction  of  this  sort  of  tissue,  which  is 
contraction. 

1  C.  B.  Davenport,  Experimental  Morphology,  Part  I,  p.  105.       2  Ibid.  p.  109. 


236 


CAUSES  OF  VARIATION 


SECTION  V  — EFFECT  OF  GRAVITY  UPON   LIVING 
MATTER1;  GEOTROPISM2 

A  germinating  seed  sends  out  two  sprouts.  From  whatever 
position  they  emerge,  one  grows  downward  in  response  to  grav- 
ity, the  other  upward  in  opposition.  In  other  words,  the  root  is 
positively  and  the  stem  is  negatively  geotropic  ;  that  is  to  say, 
0  each  contains  within  itself  some  quality  that 

j 11     puts  it  into  definite  relation  with  the  center  of 

the  earth,  but  in  opposite  directions. 

That  this  tendency  is  something  consider- 
able is  shown  by  the  fact  that  it  is  capable  of 
exertion  against  pronounced  resistance,  as  in 
burrowing  through  the  soil  or  persisting  against 
mechanical  obstructions. 

This  definite  relation  to  gravity  seems  to  ex- 
ert itself  in  the  manner  of  inward  forces  respond- 
ing to  outside  conditions  ;  for  if  a  piece  of 
stem  be  altered  in  its  position,- future  growth 
readjusts  itself  as  promptly  as  possible  in 


1  C.  B.  Davenport,  Experimental  Morphology,  Part  I, 
pp.  1 12-124  !  also  Part  H»  PP-  39 1-402,  from  which  most  of 
the  facts  here  cited  are  taken. 

2  Two  series  of  terms  are  in  use,  of  substantially  the 
same  meaning:  one  (see  "geotropism"  and  "geotropic"), 
with  endings  derived  from  the  Greek  meaning  to  turn  ;  the 
other  (see  "geotaxis"  and  "geotactic"),  with  Greek  endings 
signifying  to  arrange.    We  thus  have  also  "chemotropism," 
with  its  adjective  "  chemotropic,"  over  against  "  chemo- 
taxis,"  "  chemotactic,"  "  heliotropism,"  and  "  heliotactic," 
etc.    The  latter  endings  were  supplied  when  the  effect  of 
chemicals,  gravity,  and  light  upon  free-moving  organisms, 
as  bacteria,  swarm  spores,  etc.,  was  first  noted,  which  effects 
led  to  definite  "  arrangements  "  ;  but  when  similar  effects 
were  noted  upon  larger  organisms  not  free  to  move,  like 
the  fixed  plants,  but  which  manifested  the  effect  by  turning, 
the  term  "  tropism  "  came  into  use,  signifying  a  turning. 
This  term  and  its  derivatives  seem  to  express  more  accu- 
rately what   really  happens  in   most  cases,  and   they  are 
coming  to  be  preferred  in  all  generalized  considerations. 
Hence  in  the  text  the  term  "  geotropism  "  is  preferred  to 
"  geotaxis  "  and  similarly  in  most  places  for  all  correspond- 
ing terms. 


FIG.  25.  Influence  of 
geotropism:  be- 
havior of  a  growr- 
ing  plumule  in 
righting  itself  after 
being  placed  in  a 
horizontal  posi- 
tion, as  at  i.— 
After  C.B.  Daven- 
port, from  Stras- 
burger 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION    237 

accordance   with  this  inward  polarity  and  the  new  conditions 
(see  Figs.  25  and  26). 

Vochting's  experiments  as  here  figured,  and  as  described  by 
Morgan,1  indicate  that  the  formation  of  stem  or  of  root  is  a 


E 

FIG.  26.    Influence  of  polarity  and  of  gravity  upon  the  character  and  direction  of 
growth.  —  After  Morgan,  from  Vochting 

A,  piece  of  willow  (cut  off  in  July)  suspended  in  moist  atmosphere,  with  apex  upward;  B, 
older  piece  of  willow  (cut  off  in  March)  suspended  in  moist  atmosphere,  with  apex 
downward ;  C,  piece  of  willow  with  a  ring  removed  from  the  middle,'  apex  upward ; 
D,  piece  of  root  of  Pofulus  dilatata,  with  basal  end  upward;  shoots  from  basal 
callus;  E,  piece  of  root  of  same  with  two  rings  removed;  new  shoots  develop  from 
basal  callus  and  from  basal  end  of  each  ring 

question  of  both  internal  causes  (polarity)  and  external  influ- 
ences (gravity),  that  is  to  say,  the  character  of  growth  is  a  func- 
tion both  of  internal  and  external  conditions. 


1  Morgan,  Regeneration,  pp.  72-8^ 


238  CAUSES  OF   VARIATION 

A  stem  of  willow  severed  from  its  parent  plant  and  suspended, 
apex  upward,  in  a  moist  atmosphere,  will  of  course  send  out 
shoots  from  its  apex  and  roots  from  its  base.  If  a  ring  of  bark 
be  removed  from  the  middle  of  the  stem,  then  sprouts  will  issue 
from  the  apical  extremities  of  the  sections  and  roots  from  the 
basal  end.  Neither  of  these  experiments  determines  whether 
gravity  or  polarity  is  chiefly  instrumental  in  the  production  of 
stem  and  root,  but  if  the  piece  be  inverted  and  suspended  apex 
downward  (in  a  moist  atmosphere),  we  shall  get  some  light  on 
the  two  forces,  external  and  internal. 

Under  these  conditions  the  apical  end,  now  downward,  will 
yet  produce  stems,  but  they  will  change  their  direction  with  ref- 
erence to  the  axis  and  point  upward,  while  the  basal  end  will 
produce  roots,  but  they  will  extend  downward.  In  this  case 
each  end  has  produced  its  characteristic  growth,  and  each  has 
responded  to  gravity  in  the  usual  way  (see  Fig.  26),  except  that, 
if  the  piece  be  of  the  older  wood,  roots  will  appear  throughout 
the  entire  length.  The  force  that  fixes  the  character  of  growth 
appears  to  be  internal ;  that  which  fixes  its  direction  appears  to 
be  mainly  external. 

If  a  begonia  leaf  be  planted  in  the  ground  or  suspended  in 
moist  air,  whatever  its  position  roots  will  start  from  the  basal 
end  of  the  stem  at  its  point  of  severance,  and  afterward  shoots 
will  arise  just  above  the  point  of  origin  of  the  roots,  the  body  of 
the  leaf  withering  away.1  (By  "above"  is  meant  between  the 
origin  of  the  root  and  the  apex  of  the  leaf,  whatever  its  position.) 

By  this  we  see  that  the  stem  has  a  distinct  polarity,  producing 
sprout  and  root,  each  at  the  proper  end  ;  that  the  leaf  has  no 
true  polarity,  producing  primarily  only  roots  ;  but  that  wherever 
and  however  produced,  a  distinct  geotropism  characterizes  both 
stem  and  root. 

There  is  little  geotropism  in  leaves,  or  in  the  horizontal  stems 
of  many  plants  running  along  or  just  below  the  surface  of  the 
ground.  However,  the  stems  and  roots  produced 'at  the  nodes 
of  these  underground  stems  are  both  geotropic. 

Geotropism  in  animals.  Geotropism  is  much  less  marked  with 
animals  than  with  plants.  We  may  say  that  only  fixed  organisms 

1  Morgan,  Regeneration,  pp.  74-76. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION    239 

would  be  likely  to  develop  decided  geotropism ;  or,  conversely, 
we  may  say  that  organisms  with  marked  geotropism  would  be 
likely  to  become  fixed.  In  either  event  less  geotropism  would  be 
expected  among  animals,  and  either  assumption  would  square 
with  the  facts.  Many  lower  organisms  truly  animal  are  distinctly 
geotropic,  however,  and  most  animals  show  a  decided  preference 
as  to  position  with  reference  to  gravity.  Both  with  land  animals, 
high  or  low,  and  with  fish  as  well,  the  ventral  side  is  carried 
downward,  and  the  anterior  portion  in  general  upward. 

Effect  of  geotropism  upon  protoplasm.  The  protoplasm  of  cells, 
plant  or  animal,  is  not  homogeneous.  The  nucleus  is  heavier 
than  the  cytoplasm,  and  together  with  chlorophyll  granules  and 
starch  grains  tends  to  settle  to  the  lower  side  of  the  cell,  giving 
it  a  kind  of  polarity  due  to  gravity.  "  In  many  ova  the  yolk 
sinks  to  the  lower  pole  and  the  cytoplasm  floats  on  top,  in 
whatever  position  the  egg  may  be  held," — a  fact  which 
"  undoubtedly  has  an  important  effect  upon  development."  1 

General  effect  of  gravity  upon  development.  There  is  no  room 
for  doubt  as  to  the  profound  effect  of  gravity  upon  development. 
However,  this  influence  of  gravity  has  been  continual  and  con- 
stant on  all  existing  species  for  untold  generations,  and  it  may 
be  looked  upon  as  having  already  exerted  the  maximum  of  its 
influence  upon  all  forms  of  life. 

The  effect  of  gravity  upon  development  has,  therefore,  long 
ago  reached  the  position  of  a  constant  force  to  be  reckoned  with, 
and  is  now  to  be  regarded  as  a  fixed  factor  in  development  rather 
than  as  a  present  cause  of  individual  deviation,  —  to  be  studied 
more  for  the  sake  of  learning  the  degree  of  dependence  of  liv- 
ing matter  upon  outside  forces  rather  than  as  a  direct  means  of 
further  change. 

SECTION  VI  —  EFFECT  OF  LIGHT  UPON  LIVING  MATTER 

In  all  chlorophyllaceous  plants  the  amount  of  carbon  fixed, 
and  therefore  the  total  of  growth  in  the  sense  of  increase  in  dry 
matter,  is  in  almost  direct  proportion  to  the  expanse  of  leaf  sur- 
face and  the  amount  of  light  that  falls  upon  it. 

1  C.  B.  Davenport,  Experimental  Morphology,  Part  I,  p.  114. 


240  CAUSES  OF  VARIATION 

Light  has  other  influences,  however,  than  those  exerted 
through  the  fixation  of  carbon.  For  example,  strong  sunlight 
tends  to  check  growth  in  the  sense  of  increase  in  bulk,  and  when 
these  two  effects  of  light  are  combined,  as  they  are  in  the 
tropics,  they  give  us  naturally  the  slow-growing,  generally  small, 
and  extremely  dense  wood  of  the  lower  latitudes. 

Briefly,  light,  like  gravity,  exerts  specific  effect  upon  matter. 
Many  of  the  effects  of  gravity  (positive  geotropism)  may  be 
regarded  as  arising  from  the  elementary  properties  of  matter, 
for  naturally  all  matter  is  attracted  by,  and  approaches  as  nearly 
as  possible  to,  the  surface  of  the  earth  ;  that  is,  matter  in  general 
may  be  said  to  be  positively  geotropic.  Sensitiveness  to  light, 
however,  should  be  regarded  as  due  to  the  special  compounds 
that  constitute  living  matter,  rather  than  as  a  property  of  mat- 
ter in  general,  for  matter  in  general  is  indifferent  to  light. 

Light  exerts  influence  upon  living  matter,  especially  plants,  in 
three  distinctly  different  ways  :  (i)  through  its  heat  rays,  affect- 
ing temperatures ;  (2)  through  the  so-called  chemical  (actinic) 
rays,  causing  definite  chemical  reactions  in  the  protoplasm ; 
(3)  through  the  luminous  rays,  influencing  especially  the  direction 
of  growth  in  those  parts  that  are  so  fixed  as  to  be  incapable  of  free 
movement.  Certain  of  these  influences  are  worthy  of  somewhat 
extended  consideration. 

Chemical  effects  of  light.1  While  matter  in  general  in  its 
simpler  compounds  is  quite  indifferent  to  light,  yet  certain  com- 
pounds are  notoriously  dependent  upon  its  influence ;  that  is 
to  say,  many  combinations  are  effected  more  readily  and  others 
only  in  the  presence  of  light  (photosynthesis). 

Oxidation  of  vegetable  oils  is  much  more  rapid  in  daylight 
than  in  darkness.  Hydrogen  and  chlorin  unite  explosively  in 
the  presence  of  light.  Chlorin  passed  through  alcohol  in  strong 
sunlight  unites  with  it,  forming  chloral  hydrate,  and  chlorin 
compounds  generally  are  sensitive  to  light. 

The  whole  field  of  photography  is  dependent  upon  the  action 
of  light  upon  the  halogen  salts  of  silver,  gold,  platinum,  and 
other  metals,  due  to  the  so-called  "chemical  rays"  extending 

1  C.  B.  Davenport,  Experimental  Morphology,  Part  I,  pp.  161-165,  from  which 
most  of  the  instances  under  this  heading  are  taken. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION    241 

from  the  blue  upward  and  most  pronounced  in  the  invisible 
"ultraviolet"  portions  of  the  spectrum.  These  particular  wave 
lengths  seem  closely  akin  to  chemical  energy,  and  their  effect, 
invisible  and  subtle  as  it  is,  should  not  be  overlooked. 

Certain  organic  compounds  are  readily  formed  only  by  the 
aid  of  light;  thus  the  reaction  C14H8O2+C6H5CHO=C14H8 
(O.H)(O.CO.C6H5)  takes  place  in  sunlight,  but  in  darkness  the 
substances  are  indifferent  to  each  other.1  It  is  under  this  same 
principle  that  the  vegetable  substance  chlorophyll  is  able  to 
break  up  the  CO2  of  the  atmosphere  and  fix  the  carbon  in  the 
form  of  starch,  setting  free  the  oxygen.  This  is  the  most  dis- 
tinctive act  of  plant  life,  and  yet  it  takes  place  only  in  the  pres- 
ence of  light.  The  student  is  therefore  prepared  to  realize  that 
light  is  one  of  the  controlling  forces,  not  only  in  effecting 
chemical  compounds  in  the  non-living  world  but  in  the  activi- 
ties of  living  matter  as  well ;  that  in  many  respects  its  action  is 
fundamental  (as  in  the  fixing  of  carbon),  in  others  incidental, 
and  in  still  others  even  accidental  (as  in  the  color  of  chloro- 
phyll or  of  gold  or  silver).  In  any  event  it  is  an  influence  to 
be  taken  account  of  when  one  is  engaged  in  the  study  of  the 
circumstances  that  control  the  activities  of  living  matter. 

Effect  of  light  upon  functional  activity.2  The  effects  of  sun- 
light upon  growth  are  of  three  kinds,  —  one  due  to  the  heat 
rays  of  the  lower  spectrum,  the  others  to  the  luminous  and  the 
so-called  chemical  or  "actinic"  rays  of  the  upper  spectrum,  from 
the  blue  to  a  considerable  distance  beyond  the  violet.  Strange 
as  it  may  seem,  the  influence  of  light  upon  the  fixation  of  car- 
bon is  greatest  in  the  thermic  rather  than  in  the  actinic  region 
of  the  spectrum.  Timiriazeff3  kept  a  plant  in  the  darkness 
until  the  starch  in  the  leaves  had  been  absorbed.  "Then  in  a 
dark  room  a  prismatic  spectrum  was  thrown  upon  the  leaf  and 
the  position  of  Fraunhofer's  lines  indicated  on  the  leaf.  After 
three  to  six  hours  starch  had  formed  under  the  influence  of  the 
light,  only  in  the  region  of  the  absorption  bands  of  chlorophyll 
lying  between  B  and  D"  as  determined  by  treating  first  with 

1  C.  B.  Davenport,  Experimental  Morphology,  Part  I,  p.  163. 

2  Ibid.  Part  I,  pp.  166-180  ;  Part  II,  pp.  416-436. 

3  Ibid.  Part  I,  pp.  169-170.    The  italics  are  mine. 


242  CAUSES  OF  VARIATION 

alcohol  to  decolorize,  and  then  with  iodin,  which  forms  its  char- 
acteristic blue  with  starch.  The  spectrum  between  B  and  D1 
includes  the  upper  part  of  the  red,  the  orange,  and  the  lower 
parts  of  the  yellow,  —  the  thermic  rather  than  the  actinic 
portion  of  the  spectrum. 

Among  both  plants  and  animals  light  has  an  important  influ- 
ence upon  color.  The  chlorophyll  of  plants  is  formed  only  in 
its  presence,  and  it  is  intimately  concerned  in  the  production  of 
pigments  in  the  skin.  Not  only  that,  but  the  arrangement  and 
position  of  pigmentary  matter,  whether  lying  next  the  surface 
and  well  diffused  —  thus  giving  color  to  the  animal  —  or  lying 
collected  in  masses  deeper  in  the  skin  and  having  little  effect 
upon  the  color,  are  due  largely  to  the  direct  effect  of  light 
falling  upon  the  skin  of  the  animal.  In  this  way  certain  animals, 
as  the  chameleon,  are  capable  of  exhibiting  a  considerable  range 
of  colors,  giving  rise  to  the  fiction  that  they  are  able  to  imitate 
any  color  near  which  they  may  be  situated.2 

It  has  been  customary  to  cite  the  fact  that  cave  animals  are 
frequently  less  highly  colored  than  their  congeners  of  the  land, 
as  evidence  that  color  is  fundamentally  dependent  upon  light. 
This  cannot  be  true  except  in  a  very  general  sense.  All  material 
substances  have  some  relation  to  light  and  therefore  have  some 
color.  What  the  color  of  a  body  may  be  is  therefore  dependent 
primarily  upon  its  composition,  and  in  this  sense  its  color  may 
be  said  to  be  accidental, — a  remark  that  is  as  true  of  chlorophyll 
as  it  is  of  gold  or  silver,  or  of  red,  white,  or  yellow  brick. 

But  when  the  particular  compound  happens  to  be  one  like 
chlorophyll,  or  a  pigment  that  can  be  formed  only  in  the  presence 
of  light)  then  and  then  only  can  color  be  said  to  depend  upon 
the  presence  of  light.  Deep-sea  fishes  are  often  highly  colored ; 
rocks  hidden  in  the  earth  have  their  characteristic  tint ;  the 
blood  of  vertebrates  is  red,  not  from  the  presence  of  light  but 
from  the  presence  of  compounds  of  iron.  In  all  these  cases 
the  color  arises  from  a  substance  in  no  sense  dependent  upon 
light  for  its  formation  and  existence,  and  the  case  is  distinct 

1  The  vibrations  at  this  point  are  approximately  525  x  io12  per  second  (525,- 
000,000,000,000). 

2  C.  B.  Davenport,  Experimental  Morphology,  Part  I,  pp.  192-194. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION 


243 


from  one  in  which  the  color  is  due  to  a  substance  formed  only 
by  the  aid  of  light.  It  is  only  in  this  latter  case  that  light  may 
truly  be  said  to  be  a  direct  external  cause  of  variation. 

Examples  of  this  are  found  in  the  coloring  of  fruit,  either 
under  normal  conditions  or  in  "  fruit  photography,"  a  process 
by  which  pictures  may  be  made  to  appear  on  highly  colored 
fruit  by  shading  with  a  screen  derived  like  a  negative  from  the 
picture  to  be  transferred.1 

The  sun  is  supposed  to  exert  a  direct  effect  upon  the  skin, 
ranging  from  the  tan  of  the  white  man  to  the  dark  color  of  the 
tropical  races.  This  seems  an  ill  adaptation,  and  so  it  is  as 
regards  the  heat,  for  black  objects  are  warmer  than  white  ones ; 
but  the  adaptation  is  not  to  the  heat  rays  but  to  the  chemical, 
for  black  pigment  is  almost  totally  non-actinic.  Hence  we  may 
say  that  dark-skinned  people  have  lost  something  in  heat  resist- 
ance, but  they  have  gained  what  is  of  more  consequence, — a 
screen  against  the  actinic  rays.2 

Light  exhibits  its  most  characteristic  effect  upon  the  eye  of 
higher  animals.  It  here  gives  rise  to  two  remarkable  actions,  — 
muscular  contraction  of  the  iris,  by  which  the  amount  of  light 
admitted  is  regulated,  and  a  nerve  stimulus,  which  forms  a  defi- 
nite image  on  the  retina,  as  upon  a  mirror,  and  which  is  perfectly 
comprehended  by  the  mind.  Whether  the  colors  and  images 
seen  by  all  eyes  are  absolutely  identical  is  obviously  a  matter 
that  can  never  be  determined.  It  is  of  course  safe  to  assume 
that  the  images,  in  so  far  as  form  is  concerned,  are  identical, 
because  the  outlines  are  due  to  the  mechanical  laws  of  refrac- 
tion, but  the  colors  as  comprehended  may  be  due  in  part,  if  not 
entirely,  to  physiological  peculiarities.  That  is,  the  color  which 
to  one  is  red  may  look  to  him  as  yellow  does  to  another,  —  a 
supposition  entirely  plausible  when  we  remember  that  with 
some  individuals  sound  always  suggests  color  as  well,  so  that 
the  name  Jones  immediately  suggests  black,  or  red,  or  some 
other  color,  differing  with  different  individuals.  What  relation 
or  coordination  between  the  auditory  and  the  optic  nerves  can  be 
responsible  for  this  sort  of  mixed  impression  we  do  not  know. 

1  Literary  Digest,  September  16,  1905,  p.  381. 

2  Ibid.  October  7,  1905,  p.  485. 


244 


CAUSES  OF  VARIATION 


Vital  limits.  Chlorophyllaceous  plants  are  absolutely  depend- 
ent upon  light  for  their  very  existence,  but  parasitic  plants, 
and  animals  in  general,  are  not  dependent  upon  light  in  any 
vital  sense,  because  they,  like  animals,  subsist  upon  highly 
organized  materials  in  which  the  fixation  of  carbon  has  been 
already  accomplished  by  other  organisms.1 

All  known  facts  indicate  that  animal  life  in  general  is  essen- 
tially successful  in  total  darkness.  Mules  have  been  kept  in 
mines  for  twenty  years,  and  beyond  temporary  sensitiveness  of 
the  eyes  no  effect  was  perceptible.  Prisoners  have  spent  their 
lives  in  dungeons.  All  embryonic  development  in  mammals  takes 
place  in  the  total  darkness  of  the  mother's  body.  It  is  doubtless 
not  too  much  to  say  that  light  has  no  effect  whatever  upon  the 
vital  functions  of  the  higher  animals ;  that  it  is  as  unessential 
in  this  respect  to  animals  as  it  is  indispensable  to  plants. 

Bacteria,  as  a  rule,  not  only  do  not  need  the  light,  and  flourish 
best  in  darkness,  but  strong  sunlight  is  almost  uniformly  and 
quickly  fatal ;  indeed,  direct  sunlight  is  recognized  as  one  of 
the  most  successful  germicides  (which  is  of  itself  the  principal 
reason  why  plenty  of  light  should  be  provided  wherever  domestic 
animals  are  kept).  This  fact  is  illustrated  by  inoculating  a  gela- 
tin plate  uniformly  with  bacteria,  as  Bacillus  anthracis^  covering 
the  plate  with  a  piece  of  black  paper  out  of  which  some  pattern 
is  cut,  as  the  letter  E,  and  exposing  it  all  to  strong  sunlight  for 
a  few  hours.  If  the  plate  is  then  put  into  an  incubator  the  bac- 
teria will  grow,  except  over  the  area  exposed  to  the  light,  in 
which  area  they  have  been  killed.2  From  the  well-known  fact 
that  bacteria  in  a  vacuum  are  not  affected  by  light  we  conclude 
that  death  is  due  to  oxidation  in  the  presence  of  light,  a  phe- 
nomenon common  in  organized  compounds. 

Light  rigor.  The  movements  of  protoplasm  in  general  are 
retarded,  or  even  stopped,  in  the  presence  of  intense  light, 
so  that  rigor  precedes  death.  There  is  therefore  (for  plants) 
an  optimum,  minimum,  and  maximum  intensity,  and  between 

1  This  is  written  in  general  terms,    and  regardless   of  the  fact  that  certain 
lower  organisms,  whose  nearest  relatives  are  distinctly  animal,  themselves  bear 
chlorophyll. 

2  C.  B.  Davenport,  Experimental  Morphology,  Part  I,  pp.  171-172. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION    245 

these  limits  protoplasm  is  stimulated  by  sudden  changes,  rapidly 
becoming  accustomed,  however,  to  alterations  within  a  narrow 
range  (phototonus),  and  soon  resuming  its  normal  activity, 
except  that  as  the  intensity  approaches  the  point  of  rigor  activ- 
ity appears  to  be  permanently  checked. 

Retarding  effect  of  light  upon  the  rate  of  growth.  To  the 
higher  organisms  generally,  sunlight,  however  intense,  is  not 
fatal,  but  it  not  infrequently  retards  the  rate  of  growth,  espe- 
cially among  plants.  This  accounts  for  the  relatively  slower 
growth  of  tropical  vegetation  as  compared  with  that  of  higher 
latitudes,  and  for  the  fact  that  growth  in  the  sense  of  increase 
in  bulk  is  more  rapid  at  night  than  in  the  daytime.  Sachs 
found  1  that  the  curve  of  growth  reached  its  greatest  height  at 
daylight,  then  commenced  to  decline,  reaching  its  minimum  a 
little  before  sunset.  Davenport  points  out  that  this  fluctuation 
is  opposed  to  the  effects  of  temperature,  which  is  more  favor- 
able in  the  day  than  at  night,  so  that  the  final  results  are  some- 
what less  than  the  total  influence  due  to  light. 

This  fact  is  well  illustrated  in  experiments  upon  seedlings, 
grown  both  in  darkness  and  in  light, — investigations  that  are 
entirely  feasible,  because  at  this  stage  the  young  plant  depends 
upon  the  old  seed  for  its  nourishment.'  It  is  invariably  found  that 
seedlings  grown  in  the  darkness  have  grown  at  the  faster  rate. 

That  different  rays  have  different  effects  upon  the  growth  of 
plants  is  easily  shown.  Flammarion  cultivated  sensitive  plants 
for  three  and  a  half  months  (July  4  to  October  22)  in  red,  green, 
white,  and  blue  light.  At  the  close  of  the  experiment  the  plants 
had  attained  heights  as  follows  :  in  the  red  light,  420  mm. ;  in 
the  green,  152  mm.  ;  in  the  white,  100  mm. ;  and  in  the  blue, 
27  mm.,  with  general  appearances  shown  in  Fig.  27. 

In  this  experiment  the  greatest  heat  rays  were  of  course  trans- 
mitted with  the  red  light,  but  the  general  temperature  was  regu- 
lated by  currents  of  air  passing  through  the  various  chambers.2 

It  has  been  roughly  stated  that  light  has  no  effect  upon 
germination.  In  general  this  is  true,  though  careful  experiments 
indicate  that  most  seeds  germinate  slightly  earlier  in  darkness 

1  C.  B.  Davenport,  Experimental  Morphology,  Part  II,  p.  421. 

2  Ibid.  pp.  427-429. 


246 


CAUSES  OF   VARIATION 


than  in  light,  and  a  few,  prominent  among  which  are  the  poas, 
germinate  more  readily  in  the  light,  as  do  also  the  spores  of  ferns 
and  the  seeds  of  the  mistletoe.1 

Evidence  as  to  whether  sunlight  influences  the  growth  of  ani- 
mals is  inconclusive.  Experiments  have  been  conducted  with 
tadpoles,  snails,  the  eggs  of  certain  fish,  and  with  the  young  of 
higher  animals,  but  while  slightly  better  growth  is  reported 


Red  Green  White  Blue 

FIG.  27.  Effect  of  light  upon  rate  of  growth :  sensitive  plants  grown  for  three 
and  a  half  months  in  red,  green,  white,  and  blue  light.  —  After  C.  B.  Daven- 
port, from  Flammarion 

during  daylight,  it  is  not  certain  that  other  conditions  did  not 
contribute  to  the  results.2  Experiments  in  feeding  fattening  ani- 
mals in  darkness  and  in  light  fail  to  establish  special  differences. 
All  considerations  point  to  the  conclusion  that  light  exerts  a 
strongly  modifying  influence  upon  living  matter  in  general,  but 
that  the  higher  animals  are  substantially  free  from  its  direct 
effect  except  to  some  extent  in  the  matter  of  color. 

1  C.  B.  Davenport,  Experimental  Morphology,  Part  II,  pp.  419  and  424. 

2  Ibid.  pp.  425-426. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION    247 

Influence  of  light  upon  the  direction  of  locomotion  or  of  growth ; 
heliotropism.  Irritability  to  light  is  one  of  the  properties  of 
protoplasm.  This  reaction  is  generally  in  the  form  of  contrac- 
tion, as  with  muscle  fiber 1  resulting  in  a  shortening  of  the  side 
next  the  source  of  light.  With  free-moving  plants  and  animals 
this  gives  direction  to  locomotion,  and  they  gradually  swing 
about  until  both  sides  are  equally  lighted,  when,  if  motion 
continues,  the  creatures  will  of  necessity  progress  toward  the 
light.  This  is  positive  heliotropism.  Quick-moving  forms  are 
often  carried  into  the  source  of  light  by  their  very  impetus, 
before  the  repellent  effect  of  great  heat  has  time  to  act.  In 
this  way  moths  fly  into  the  candle  and  are  killed,  while  slower- 
moving  forms  are  checked  by  the  heat  in  time  to  save  them- 
selves. In  this  latter  case  the  future  movements  will  be  a 
resultant  of  the  positive  heliotropism  and  negative  thermotrop- 
ism, by  which  the  insects  are  held  at  a  certain  radius  circling 
about  the  source  of  both  light  and  heat,  as  if  not  able  to  leave 
it,  as  indeed  they  are  not. 

Negatively  heliotropic  forms,  like  earthworms,  are  those  whose 
protoplasm  does  not  contract  in  the  presence  of  light,  but,  on  the 
contrary,  expands.  These  are  carried  away  from  the  light,  and 
if,  in  their  wanderings,  a  lighted  area  is  approached,  they  are 
unable  to  enter  it. 

When  the  organism  is  not  free  to  move,  as  in  the  case  of 
stems  of  higher  plants,  the  effect  will  be  manifested  in  the  direc- 
tion of  growth,  which  is  all  the  response  to  heliotropism  pos- 
sible under  the  circumstances.  In  cases  of  this  kind  the  stem 
will  bend  toward,  or  away  from,  the  source  of  light,  according 
as  the  plant  is  negatively  or  positively  heliotropic,  until  all 
sides  are  equally  lighted,  in  which  position  it  will  remain  during 
growth,  as  do  other  forms  during  locomotion. 

This  placing  of  the  body  (or  stem)  with  reference  to  the 
various  "  tropisms  "  is  technically  known  as  "orientation,"  and 

1  As  most  of  the  examples  to  follow  are  confined  to  the  lower  animals,  and  to 
plants  in  which  protoplasm  is  comparatively  exposed,  it  is  well  to  remind  the 
student  that  the  higher  animals  are  not  destitute  of  the  same  properties,  and  that 
they  have  one  exposed  region  peculiarly  sensitive  to  light,  namely  the  iris  of  the 
eye,  whose  muscles  contract  promptly  under  its  influence. 


248  CAUSES  OF  VARIATION 

this  particular  orientation  with  reference  to  the  rays  of  light, 
whether  parallel  to  their  direction  or  transverse,  has  received 
the  special  name  of  "  phototaxis."  l 

Effective  rays.  All  experiments  indicate  that  the  blue  rays 
are  the  effective  ones  in  producing  heliotropic  effects.2  Some 
organisms  seem  sensitive  to  the  yellow,  but  both  red  and  ultra- 
violet are  alike  inoperative.  Heliotropism  is  therefore  an  effect 
decidedly  due  to  the  luminous  rays. 

Contributary  conditions.3  Heliotropism  is  dependent  upon  a 
variety  of  conditions  both  external  and  internal  to  the  organism. 

1  There  is  great  uncertainty  as  to  terms.    The  one  just  quoted  ("phototaxis  ") 
is  in  its  root  a  protest  against  the  old  term  "  heliotropism  "  in  that  it  recognizes 
light  as  the  active  agent  rather  than  the  sun  (helios),  which  is  a  source  not  only  of 
light  but  of  heat  and  chemical  energy  as  well;  and  it  recognizes,  too,  that  these 
influences  are  exerted  as  light,  quite  independent  of  the  sun  or  any  other  particu- 
lar source. 

Of  late  there  has  been  a  strong  disposition  to  substitute  this  root  for  the  older 
term,  giving  us  phototropism  in  place  of  "  heliotropism."  Those  disposed  to  this 
view  would  go  farther  and  discriminate  between  those  movements  that  appear  to 
occur  with  reference  to  the  direction  of  the  rays,  which  is  "  phototaxis,"  and  those 
which  are  made  with  reference  to  the  intensity  of  illumination,  which  is  "  photop- 
athy."  These  students  also  recognize  the  fact  that  irritability  and  the  consequent 
movements,  whether  positive  or  negative,  depend  very  much  upon  the  intensity, 
so  that  organisms  that  are  negatively  heliotropic  at  high  intensity  are  positively 
heliotropic  at  low  intensity,  suggesting  a  middle  point  at  which  the  organism  will 
be  Reid,  as  with  deep-sea  animals  that  come  near  the  surface  at  night  but  sink  to 
considerable  depths  in  the  bright  light  of  day,  the  water  acting  as  a  screen.  This 
neutral  point  or  satisfied  condition  is  described  as  "  phototonus." 

It  may  be  necessary  to  recognize  all  these  distinctions  when  the  subject  is 
better  understood,  but  it  is  more  than  likely  that  these  different  behaviors  are 
only  different  manifestations  of  the  same  natural  irritability  to  light  on  the  part  of 
protoplasm  in  general,  and  that  the  so-called  "  phototaxis  "  or  even  "phototonus  " 
is  only  the  condition  of  the  organism  after  it  has  brought  itself  into  such  position 
that  one  irritability  is  balanced  by  another  (which  is  always  easy  with  bilateral 
symmetry),  or  that  it  is  a  kind  of  acclimatization  acquired  by  the  protoplasm  to 
the  particular  intensity  at  hand. 

The  theoretical  objection  to  direct  reference  to  the  sun  is  certainly  sound.  The 
attraction  (or  repulsion)  is  with  reference  to  light  as  light,  and  not  to  the  sun  as 
its  source.  But  the  sun  is  preeminently  the  source  of  light,  and  for  this  reason, 
and  with  a  proper  understanding  of  the  facts,  the  author  prefers  for  our  purposes 
to  adhere  to  the  single  old  term,  at  least  under  the  present  state  of  kriowledge, 
for  if  properly  understood  it  seems  substantially  correct  and  serves  all  practical 
purposes  fairly  well. 

2  C.  B.  Davenport,  Experimental  Morphology,   Part  I,  pp.  201-203;    Loeb, 
Studies  in  General  Physiology,  pp.  29-31. 

8  Ibid.  pp.  196-201. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION    249 

It  is  first  of  all  dependent  upon  intensity  of  light,  feeble  illumi- 
nation being  ineffective,  even  if  the  characteristic  rays  be  pres- 
ent. Not  only  that,  but  some  organisms  are  positively  helio- 
tropic  in  moderate  light  and  negatively  heliotropic  in  strong 
light.  In  this  way  many  fishes  are  held  in  a  nearly  constant 
illumination,  rising  or  falling  in  the  water  according  to  the 
intensity  of  sunlight,  and  coming  completely  to  the  surface  at 
nightfall. 

Another  element  in  heliotropism  is  temperattire,  its  influence 
being  most  active  at  the  maximum  or  normal,  and  lessening  or 
disappearing  as  it  falls. 

Still  another  controlling  influence  is  the  condition  of  the 
animal.  Many  caterpillars  are  positively  heliotropic  only  when 
unfed.  They  are  thus  led  to  ascend  trees  when  hungry  and  to 
descend  when  filled.1  Still  again,  certain  animals  are  heliotropic 
only  under  peculiar  circumstances  ;  for  example,  Loeb  found  that 
winged  ants  exhibited  no  reaction  to  light  except  at  the  time  of 
their  nuptial  flight,  when  they  were  decidedly  heliotropic.2 

Influence  of  light  upon  the  direction  of  growth.3  Instances  of 
this  influence  upon  the  stems  of  plants  are  almost  too  common 
to  need  mention.  The  leaning  of  plants  toward  the  window,  or 
of  trees  over  a  stream,  can  be  seen  almost  any  day. 

It  is  noticeable  that  most  leaves  appear  to  be  destitute- of 
heliotropism,  and  yet  it  is  not  impossible  to  detect  traces  of  its 
influence.  On  careful  observation  it  will  be  noted  that  some 
leaves  tend  to  present  their  upper  surface  at  right  angles  to 
light  rays,  while  others  tend  to  present  the  edge. 

It  is  a  general  principle  of  orientation  that  organisms  with 
radial  symmetry,  like  most  plants,  present  as  nearly  as  possible 
the  end  of  the  long  axis  to  the  source  of  light,  with  the  lateral 
parts  equally  lighted ;  while  organisms  of  bilateral  symmetry, 
like  most  animals,  tend  to  present  the  dorsal  surface  at  right 
angles  to  the  light,  with  the  oral  (head)  end  nearest  its  source, 
the  right  and  the  left  halves  equally  lighted,  and  the  ventral 
surface  shaded. 

1  Loeb,  Physiology  of  the  Brain,  p.  189. 

2  Loeb,  Studies  in  General  Physiology,  pp.  52-53. 

3  C.  B.  Davenport,  Experimental  Morphology,  Part  II,  pp.  437~445- 


250 


CAUSES  OF  VARIATION 


In  the  very  highest  animals  little  but  the  eye  is  sensitive  to 
light,  most  parts  being  protected  by  a  heavy  epidermis  or  other 
covering,  so  that  heliotropism  in  its  strictest  sense  is  in  them 
limited  to  the  visual  parts.  In  lower  animals,  however,  with 
bodies  less  protected,  light  exerts  a  controlling  influence  upon 
movements. 

Influence  of  light  upon  the  direction  of  locomotion.1  It  has 
already  been  explained  that  some  animals  exhibit  heliotropism 
only  at  certain  periods  of  their  lives,  or  only  in  certain  condi- 
tions, as  when  hungry.  Others,  however,  are  constantly  and 
uniformly  sensitive.  The  common  house  fly  is  positively  helio- 
tropic,  while  the  larvae  of  the  same,  hatched  in  the  dark,  soon 
become  strongly  negative,  and  so  continue  while  in  the  larval 
condition.2 

This  difference  between  the  larval  and  adult  stage  is  common, 
and  led  Loeb  at  first  to  suppose  it  to  be  a  general  principle,  — 
a  conclusion  invalidated  by  the  fact  that  caterpillars  and  their 
imagoes  behave  alike.2 

Both  moths  and  butterflies  are  positively  heliotropic,  but 
moths  are  "  attuned "  to  a  lower  intensity.  This,  with  their 
more  rapid  flight,  is  responsible  for  their  wholesale  destruction 
by  the  naked  flame,  which  the  slower-flying  butterflies  avoid  as 
a  source  of  heat. 

The  tendency  of  many  small  animals  to  creep  into  crevices  as 
if  to  hide  must  not  be  understood  as  evidence  of  negative  helio- 
tropism, much  less  as  evidence  of  timidity.  It  is  often  due  simply 
to  contact  irritability  (stereotropism),  for  it  is  a  well-established 
fact  that  living  matter  is  sensitive  to  contact  with  other  solid 
substances.  This  is  the  principle  discussed  in  Section  IV  and 
the  one  that  generally  lies  at  the  basis  of  the  huddling  together 
of  individuals,  or  of  their  crowding  into  corners  or  crevices. 
Loeb  brought  out  this  principle  very  nicely  with  some  negatively 
heliotropic  butterflies  which  wedged  themselves  closely  between 
two  plates  of  glass  in  the  presence  of  light,  showing  how  one 
tropic  influence  —  in  this  case  contact  irritability  —  is  competent 

1  C.  B.  Davenport,  Experimental  Morphology,  Part  I,  pp.  180-210;  Loeb, 
Studies  in  General  Physiology  (1905),  pp.  1-114,  from  which  most  of  the  examples 
are  cited.  2  Loeb,  Studies  in  General  Physiology,  p.  20. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION 


251 


to  overcome  an  opposite  but  weaker  one,  —  in  this  case  nega- 
tive heliotropism. 

It  is  a  noteworthy  fact  that  irritability  to  light,  while  a  prop- 
erty of  protoplasm  in  general,  is  more  pronounced  in  some  cases 
than  in  others,  even  within  the  same  organisms.  This  is  true 
not  only  in  the  eyes  of  animals,  but,  in  general,  the  oral  (anterior) 
end  of  eyeless  animals  is  much  more  sensitive  to  light  than  is 
the  aboral ; 1  as  also  is  the  dorsal  surface  more  sensitive  than 
the  ventral.  Light  therefore  operates  strongly  to  influence  not 
only  the  position  but  the  locomotion  of  animals  as  well. 

The  following  conclusions  from  Loeb  upon  the  influence  of 
light  are  valuable.2  In  substance  they  are  : 

I.  "  The  dependence  of  animal  movements  on  light  is  in  every 
point  the  same  as  the  dependence  of  plant  movements  on  the 
same  source  of  stimulation." 

1.  "  The  direction  of  the  median  plane  or  the  direction  of 
the   progressive   movements  of    an  animal  coincides  with  the 
direction  of  the  rays  of  light." 

2.  "  The  more  refrangible  rays  of  the  visible  spectrum  are 
more  effective  than  the  less  refrangible  rays." 

3.  "  Light  of  a  constant  intensity  acts  as  a  constant  stimulant." 

4.  Heliotropism  is  in  a  large  measure  dependent  upon  the 
intensity  of  light,  differing  for  different  animals. 

5.  "  Heliotropic  movements  occur  only  between  certain  limits 
of  temperature." 

II.  "  The  orientation  of  an  animal  toward  a  source  of  light 
depends  on  the  form  of  the  body,  just  as  the  orientation  of  a 
plant  to  light  depends  on  the  form  of  the  plant." 

1.  "  Symmetrical  points  on  the  surface  of  dorsiventral  animals 
possess  equal  irritabilities." 

2.  The  "  irritability  of  the  oral  pole  of  an  animal  is  different 
from  the  irritability  of  the  dorsal  pole,"  and  is  generally  greater. 

3.  "  The  irritability  of  the  ventral  surface  is  different  from  the 
irritability  of  the  dorsal  surface." 

"  These  three  conditions  taken  together  cause  dorsiventral 
animals  to  place  their  median  planes  in  the  direction  of  the 

1  Loeb,  Studies  in  General  Physiology,  pp. 

2  Ibid.  pp.  81-84. 


252 


CAUSES  OF  VARIATION 


rays  and  to  move  toward  or  away  from  the  source  of  light  in 
this  direction." 

4.  "  Eyeless  animals  behave  in  this  respect  like  animals  hav- 
ing eyes." 

III.  "  Heliotropic  irritability  of   an  animal   manifests  itself 
frequently  only  at  certain  epochs  of  its  existence." 

1-4.  In  winged  ants  this  epoch  is -at  the  nuptial  flight;  in 
plant  lice  it  is  when  the  wings  are  present ;  in  the  larvae  of 
Musca  vomitoria  negative  heliotropism  is  most  prominent  when 
the  larva  is  fully  grown ;  and  in  a  large  number  of  animals  the 
irritability  is  opposite  in  the  larval  and  in  the  adult  stages. 

5.  "  Both  night  and  day  Lepidoptera  are  positively  heliotropic, 
and  their  heliotropism  is  similar  to  that  of  every  other  positively 
heliotropic  animal.    The  period  of  sleep  of  the  night  Lepidop- 
tera, however,  falls  in  the  daytime,  and  only  for  this  reason  is 
their  heliotropism  manifested  exclusively  at  night."  l 

IV.  "  In  many  animals  heliotropic  irritability  is  connected 
with  sexuality."    Ants  are   sensitive   only  at   the   time   of  the 
nuptial  flight,  and  in  both  ants  and  Lepidoptera  the  males  are 
more  sensitive  than  the  females. 

V.  "  The  behavior  of  an  animal  depends  on  the  sum  total  of 
its  different  forms  of  irritability." 

VI.  Many   animals    are   "  compelled   to    orient   their  bodies 
against  the  surfaces  of  other  solid   bodies,"  or  to  bring  their 
bodies  "  in  contact  with  other  solid  bodies  on  as  many  sides 
as  possible  (stereotropism)." 

VII.  Animals  "  may  be  forced  by  light  to  move  from  diffused 
light  into  sunlight  and  to  remain  exposed  to  the  high  tempera- 
ture of  the  sunlight,  even  though  it  may  cause  their  death." 

Considering  all  the  "  irritabilities  "  and  "  tropisms  "  to  which 
animals  and  plants  are  exposed  and  to  which  they  react,  it  is 
not  necessary  to  appeal  to  instinct,  or  even  to  the  nervous 
system,  to  explain  all  movements  of  animals,  nor  is  it  well  to 
ascribe  to  them  such  anthropomorphic  qualities  as  love  of  light, 
distaste  for  darkness,  preference,  avoidance,  curiosity,  reason,  or 
other  such  bases  of  higher  intelligent  action. 

1  The  question  naturally  arises,  Why  is  the  daytime  the  period  for  sleep  in  a 
positively  heliotropic  animal  ?  The  answer  has  not  yet  been  given. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION    253 


To  these  conclusions  two  observations  may  well  be  added  for 
present  purposes  : 

i.  Heliotropism,  like  many  other  reactions  of  protoplasm, 
arises  from  the  nature  of  the  organism,  and  not  necessarily  from 


11:22 


i 

V" 

d 


(2).  14:OO  to  14:2O 


11:12 


11:02 


10:55 


10:44 


12:49 


14:21 


10:28 


14:24 


14:19 


(3).  14:20  to  14:34 


FIG.  28.  Effect  of  light  upon  locomotion : 
movements  of  an  amoeba  in  response 
to  changing  directions  of  .light.  Ar- 
rows show  the  direction  of  the  light 
rays,  and  figures  show  the  hour  (13=  i 
o'clock,  etc.).  — After  Davenport 


12:54 


'(1).  12:48  to  14:00 


a  basis  of  utility.  For  example,  roots  are  in  general  positively 
heliotropic,  —  a  quality  that  is  not  of  the  slightest  usefulness, 
and  which  must  be  regarded  as  entirely  accidental.  Again,  this 


254  CAUSES  OF  VARIATION 

quality  is  often  fatal,  as  in  the  case  of  moths.  In  general,  how- 
ever, matters  have  long  since  become  adjusted  to  these  reactions 
as  to  other  necessities  governing  the  behavior  of  living  matter. 

2.  All  experiments  indicate  a  high  degree  of  variability  among 
individuals,  not  only  as  regards  the  degree  of  response  to  heliot- 
ropism,  but  also  as  regards  the  effect  of  all  other  outside  influ- 
ences, even  that  of  poisons. 

Among  examples  furnished  by  the  extended  investigations 
into  this  subject,  we  have  space  to  note  but  two. 

The  amoeba,  which  represents  about  the  simplest  form  of 
animal  life,  is  an  excellent  medium  for  illustrating  sensitiveness 
to  light.  Fig.  28  exhibits  the  movements  of  one  of  these  bits  of 
living  matter  under  the  influence  of  light,  whose  direction,  as 
shown  by  the  arrows,  was  occasionally  changed,  the  figures  in- 
dicating the  hour,  —  all  of  which  is  strongly  suggestive  of  the 
process  of  driving  sheep. 

The  other  example  to  be  noted  is  the  effect  of  light  upon  the 
position  of  the  chlorophyll  granules  in  the  leaf  cells,  under  dif- 
ferent degrees  of  illumination,  whether  on  the  exterior  walls,  the 
partition,  or  the  interior  walls. 

Conditions  that  determine  heliotropism.  Some  organisms  are 
positively  heliotropic  in  one  intensity  and  negatively  so  in 
another ;  some  are  positive  at  one  temperature  and  negative  at 
another ;  some  are  positive  in  a  certain  concentration  (of  sea 
water)  and  negative  in  another,  and  the  general  principle  may 
be  stated  that  decreasing  the  concentration  has  the  same  effect 
as  increasing  the  temperature.1  It  thus  appears  that  the  same 
organism  can  often  be  made  positively  or  negatively  heliotropic 
at  will  by  altering  the  surrounding  conditions  of  life. 

SECTION   VII  —  INFLUENCE   OF   TEMPERATURE   UPON 
LIVING  MATTER 

The  relation  of  heat  to  living  matter  is  mainly,  but  not  exclu- 
sively, quantitative ;  that  is  to  say,  the  effect  of  heat  is  princi- 
pally upon  the  rate  of  growth  and  activity.  In  general,  each 
species  has  its  maximum,  above  which  protoplasm  becomes 

1  Loeb,  Studies  in  General  Physiology,  pp.  265-294. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION    255 

inactive  (heat  rigor);  its  minimum,  below  which  all  activity 
ceases  ;  and  its  optimum,  —  that  point  at  which  growth  is  most 
rapid.  Certain  facts  in  this  connection  are  noteworthy  : 

1.  The  maxima,  minima,  and  optima  are  not  the  same  for 
different  species. 

2.  Protoplasm  is  killed  if  carried  much  above  the  maximum, 
—  the  organism  decomposes  and  is  destroyed. 

3.  Temperatures  below  the  minimum  are  not  fatal  except  in 
the  presence  of  moisture,  which,  on  conversion  into  ice,  destroys 
the  structure  of  protoplasm  by  the  act  of  expansion. 

4.  The  optimum  at  which  growth  is  most  rapid  is  nearer  the 
upper  than  the  lower  limit. 

5.  Both  the  optimum  and  the  maximum  may  be  raised  by 
careful  methods  involving  gradual  acclimatization. 

Specific  effect  of  heat  upon  protoplasm.1  Beginning  at  the 
optimum  and  decreasing  both  ways  to  the  limits,  it  may  be  said 
in  general  that  protoplasmic  activity  is  in  proportion  to  the  tem- 
perature. This  is  true  of  the  amount  of  oxygen  absorbed,  of 
carbon  dioxid  evolved,  of  chlorophyll  formed,  and  of  carbon 
fixed,  —  in  other  words,  of  metabolism.  The  same  is  true  as 
to  movements  of  protoplasm  and  its  irritability  to  light,  contact, 
or  other  stimuli.  The  following  table  exhibits  the  number  of 
electric  shocks  per  second  required  at  different  temperatures  to 
produce  tetanus  in  the  neck  muscles  of  a  tortoise.2 

EFFECT  OF  TEMPERATURES  UPON  ANIMAL  ACTIVITIES 


TEMPERATURES 

SHOCKS  PER  SECOND  RE- 
QUIRED TO  PRODUCE 
TETANUS 

TEMPERATURES 

SHOCKS  PER  SECOND  RE- 
QUIRED  TO  PRODUCE 
TETANUS 

4°C. 
9°C. 

I 

5 

2I°C. 

28°  C. 

25 
34 

Effect  of  heat  upon  the  rate  of  growth  in  plants.3  The  relation 
of  temperature  to  plant  growth  is  well  shown  in  the  tables  on 
the  following  page.4 

1  C.  B.  Davenport,  Experimental  Morphology,  Part  I,  pp.  222-231. 

2  Ibid.  p.  230.  3  Ibid.  Part  II,  pp.  450-460.  *  Ibid.  p.  451. 


256 


CAUSES  OF  VARIATION 


GROWTH  IN  MILLIMETERS  OF  THE  PLUMULES  AND  THE  RADICLES  OF  SEED- 
LINGS GROWN  UNDER  DIFFERENT  TEMPERATURES  FOR  48  HOURS  (Sachs) 


PLUMULES 

RADICLES 

Temperature  C. 

Maize 

Bean 

Pea 

Temperature  C. 

Maize 

Bean 

Pea 

I4-l6° 

17.0° 

2.51 

4.01 

16-18 

4.6! 

7-41 

3.01 

25-7 

39 

18-20 

26.3 

24-5 

47 

20-22 

28.5 

34 

4I.O 

22-24 

33-2 

39-o 

30 

17.0 

24-26 

34-o 

55-o 

28 

26-28 

5.6 

II.O 

10.0 

38.2 

25.2 

22 

12.2 

28-30 

42.5 

5-9 

7 

30-32 

32-34 

II.O 

10.5 

5-7 

34-36 

13.0 

I5.0 

5-o 

36-38 

38-40 

9.1 

10.2 

5-5 

42.5 

4.6 

7-5 

MAXIMA,  MINIMA,  AND  OPTIMA  FOR  VARIOUS  SPECIES  ARRANGED 
ACCORDING  TO  THE  OPTIMA  2 


SPECIES 

OPTIMUM 

MINIMUM 

MAXIMUM 

Bacillus  phosphorescens 

20  o° 

OOO° 

770° 

Penicillium   ... 

22  O 

I   c 

47  O 

Phaseolus  multiflorus3  (bean)      .... 
Phaseolus  multiflorus  4  (bean)       .... 
Pisum  sativum  4  (pea)      

26.3 

33-7 
26.6 

9-5 
6.c 

46.2 

Sinapis  alba4  (white  mustard)      .... 
Lepidium  sativum4     
Linum  usitatissimum  4  (flax)    
Lupinus  albus  4  
Hordeum  vulgare4  (barley) 

27-4 
27.4 

27-4 
28.0 

28.7 

o.o 
1.8 
1.8 

7-5 

c  o 

37-2  + 
37-2  + 
37-2  + 

77  7 

Triticum  vulgare  4  (wheat) 

28  7 

c  o 

4-7  c 

Yeast    

28-74 

O  O  ~T" 

38  o 

Bacillus  subtilis      .              .               ... 

?o  o 

60 

CQ  o 

Bacterium  termo    

lO-7i; 

c  o 

4O  O  -r- 

Zea  mais  4  (Indian  corn)      

77.7 

Q.  C 

46.2 

Zea  mais8  (Indian  corn)      
Cucurbita  pepo  4  (gourd) 

34-o 

11  7 

177 

46  2 

Bacillus  ramosus    
Bacillus  anthracis  ....               . 

JJ-/ 

37-o 

37  o 

I3.0 

1  A  O 

4O.O 

A  C  O 

Bacillus  tuberculosis  

38  o 

7O  O 

42  O 

Bacillus  thermophilus      

6^-70 

42  O 

72.O 

1  Growth  during  96  hours. 

2  C.  B.  Davenport,  Experimental  Morphology,  Part  II,  p.  454. 
»  Radicle.  4  Plumule. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION 


257 


Commenting  on  this  table,  its  author  observes  in  substance : 

1.  That  in  general  the  optima,  the  minima,  and  the  maxima 
rise   and  fall  together ;  that  is,  a  species  with  a  high  optimum 
will  also  have  a  relatively  high  maximum  and  minimum. 

2.  That  species  vary  greatly ;  so  much  so  that  the  maximum 
of  one  (B.  phosphorescens)  may  be  below  the  minimum  of  another 
(B.  thermophilus}. 

3.  That  the  optimum  for  the  radicle  and  the  plumule  may  be 
widely  apart,  as  in  the  bean. 

4.  That,  in  general,  the  optimum  is  in  close  relation  to  the 
natural  habitat  of  the  species,  as  in  B.  phosphorescens  that  lives 
in  the  moderate  temperature  of  the  sea,  and  in  B.  thermophilus 
that  lives  in  the  high  temperature  of  decaying  manure.    From 
collateral  evidence  this  must  be  ascribed  to  acclimatization. 

5.  That  of  all  the  species  noted,  the  bacteria  have  the  greatest 
range  in  optimum,  showing  that  they  are,  as  yet  at  least,  less 
fixed  in  their  organization. 

6.  That  the  minimum  never  falls  below  o°  C.,  the  freezing 
point  of  water,  which  is  the  minimum  for  vital  activities. 

7.  That  the  maximum  temperature  tends  to  be  rather  constant 
with  related  species,  and  among  flowering  plants  the  range  is  but 
9°  (37°-46°).    But  46°  is  a  fatal  temperature  for  most  proto- 
plasm, and  50°  is  the  limit,  showing  how  near  the  limit  some 
species  have  been  pushed.    The  extraordinarily   high   temper- 
atures of  B.  thermophilus  must  be  regarded  as  an  instance  of 
acclimatization,  of  which  other  striking  examples  are  found  in 
hot  springs.1 

8.  That  the  range  from  minimum  to  maximum  varies  with  the 
species.    In  this  table  the  range  is  least  for  B.  tuberculosis  (12°) 
and  greatest  for  B.  phosphorescens  (37°). 

9.  That  the  "  wonderful  adjustment "  of  critical  temperatures 
to  the  environment  of  the  species  is   not  to  be   regarded   as 
evidence  of  selection,  but,  as  is  elsewhere  shown  under  "  Accli- 
matization," it  is  due  to  the  modification  wrought  in  the  proto- 
plasm by  the  temperature  itself. 

1  To  the  above  may  be  added  the  observation  that  the  optimum  lies  nearer 
the  upper  limit ;  that  is,  the  difference  between  the  optimum  and  the  maximum  is 
less  than  the  difference  between  the  optimum  and  the  minimum. 


258 


CAUSES  OF  VARIATION 


Effect  of  heat  upon  growth  in  animals.1  All  larger  land  animals 
have  acquired  facilities  for  maintaining  practically  a  constant  tem- 
perature. This  is  not  true  for  all  animals,  many  of  which,  like 
marine  species,  are  notably  dependent  for  their  temperature  upon 
the  accident  of  environment,  in  which  respect  they  differ  but  little 
from  plants.  It  remains  to  note,  therefore,  what  influence  heat 
may  exert  upon  the  growth  of  animal  life  so  conditioned  as  to  be 
dependent  upon  the  surroundings  for  its  temperatures. 

INCREASE  IN  LENGTH  (MILLIMETERS)  OF  YOUNG  TADPOLES  OF  FROG  AND 

OF  TOAD,  UNDER  DIFFERENT  TEMPERATURES,  FROM  THE  24.™ 

TO  THE  48TH  HOUR  AFTER  HATCHING  2 


TEMPERATURES 
C. 

AVERAGE  GROWTH 

TEMPERATURES 
C. 

AVERAGE  GROWTH 

Frog 

Toad 

Frog 

Toad 

9-11° 

4-5 

3-o 

23-25° 

41-3 

11-13 

5-3 

5-3 

25-27 

31-5 

39-o 

i3-J  5 

4-3  (?) 

'5-5 

27-29 

40.0 

15-'  7 

16.3 

29-31 

47-5 

56.8 

17-19 

9-5 

3J-33 

40.2 

55-3 

19-21 

19.8 

21.2 

33-35 

43-5 

21-23 

Twenty-nine  to  thirty-one  degrees  seems  to  be  about  the 
optimum  temperature  for  both,  from  which  the  table  shows  that 
the  land-living  toad  prospered  rather  better  under  the  higher 
temperatures  than  did  the  frog,  as  he  certainly  suffered  more 
under  the  lower,  but  that  in  both  the  rate  of  growth  was  sub- 
stantially in  proportion  to  the  temperature. 

The  author  of  the  table  reports  that  the  interval  between 
fertilization  and  hatching  in  cod  varies  from  thirty  days  at  a 
temperature  of  —  2°,  to  thirteen  days  at  a  temperature  of  6°-8°  ; 
that  herring  vary  from  forty  days  at  2°-4°,  to  eleven  days  at 
IO°-I2°;  and  that  the  time  required  for  the  frog  to- attain  a 
development  at  which  the  head  and  tail  are  sharply  denned  is,  at 
15°,  six  days  ;  at  33°,  one  day. 

1  C.  B.  Davenport,  Experimental  Morphology,  Part  II,  pp.  457-460. 

2  Ibid.  p.  457. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION    259 

Birds  develop  only  at  high  temperatures.  The  normal  tem- 
perature for  the  chick  is  38°.  Fere2  incubated  at  temperatures 
varying  from  34°  to  41°.  The  individuals  were  all  examined  at 
the  same  absolute  time,  and  the  following  figures  express  the 
percentages  of  development  attained,  taking  that  of  38°  as  the 
standard  : l 


Temperature  
'Index  of  development      .     .     . 

34° 
0.65 

35° 
0.80 

36° 
0.72 

37° 

? 

38° 

I.OO 

39° 
i.  06 

40° 
1.25 

4i° 
i-5' 

The  author  remarks  that  some  doubt  attaches  to  the  figures 
under  35°,  36°,  and  37°,  and  calls  our  attention  to  the  fact  that 
somewhere  not  far  above  41°  the  series  would  become  zero. 
But  for  the  range  given,  the  development  is  in  proportion  to  the 
temperature,  although  the  highest  given  (41°)  is  considerably 
above  that  attained  under  natural  conditions.  The  growing  chick 
therefore  does  not,  in  nature,  achieve  its  optimum. 

Effect  of  heat  upon  the  direction  of  growth,  — thermotropism.2 
Without  going  into  the  methods  of  investigation,  it  appears  that, 
independently  of  the  influence  of  light  or  other  "  tropisms,"  plants 
are  often  positively  or  negatively  thermotropic  largely  according 
to  temperatures.  The  plumule  of  seedling  maize,  for  example, 
is  known  to  be  positively  thermotropic  at  ordinary  temperatures, 
while  the  radicle  is  positive  between  15°  and  35°,  indifferent  at 
37.5°,  and  negative  above.  The  indifferent  point  with  the  bean 
(radicle)  is  given  at  22.5°. 

The'  subject  is  little  understood,  and  though  the  impulse  of 
thermotropism  is  weak  as  compared  with  that  of  heliotropism  or 
geotropism,  it  is  supposed  to  be  one  which  inclines  the  organism 
to  align  itself  in  accord  with  the  direction  of  heat  rays,  although 
it  is  true  that  thermotropic  plants  are  sensitive  to  conducted  as 
well  as  to  radiant  heat. 

Temperature  limits  of  life.3  All  experiments  indicate  that  as 
the  temperature  rises  above  the  maximum  the  first  effect  is  heat 

1  C.  B.  Davenport,  Experimental  Morphology,  Part  II,  p.  459- 

2  Ibid.  pp.  463-467. 

3  For  extended  discussion,  and  for  tables  of  temperature  limits,  see  C.  B.  Daven- 
port, Experimental  Morphology,  Part  I,  pp.  231-249. 


260  CAUSES  OF  VARIATION 

rigor,  which  soon  passes  into  death.  The  more  rapid  the  rise 
the  lower  the  death  point,  and  the  more  gradual  the  rise  the 
greater  the  resistance.  Again,  if  the  temperature  does  not  rise 
too  high,  the  heat  rigor  may  gradually  pass  off,  and  activity  may 
be  resumed,  even  at  temperatures  which  at  first  were  followed 
by  entire  suspension  of  activity,  and  even  by  rigor.  This  is  the 
first  stage  in  the  process  of  acclimatization. 

Sachs  found  that  a  sensitive  plant  kept  at  "  40°  C.  for  one  hour 
suffered  loss  of  sensibility  during  twenty  minutes  after  removal.' 
Raised  slowly  to  50°,  sensibility  was  only  temporarily  lost,  but 
52°  proved  fatal.  Immersed  in  water,  heat  rigor  occurred  at  a 
temperature  5°  to  10°  lower."  1  Hofrneister  found  that  hairs 
from  the  stem  and  leaf  of  Ecballium  agreste,  showing  lively 
movement,  when  gradually  raised  from  i6°-i7°  C.  to  40°  C. 
"became  motionless,"  but  that  "  after  one  or  two  hours  move- 
ment returned  and  was  very  violent.  Cooled  and  raised  again  to 
45°  C.,  the  protoplasm  was  motionless  at  first,  but  after  seven- 
teen minutes  movements  recurred  but  were  not  rapid."  2 

The  vital  limit  varies  greatly  with  the  species.  Thus,  roughly 
speaking,  for  bacteria  it  is  45°  C.;  for  cryptogams,  generally 
45°-5O°,  with  an  occasional  one  at  60°;  flowering  plants, 
45°-5°°;  protozoa,  4O°-45°,  with  a  few  as  high  as  60°;  mol- 
lusks,  30°-4O°  ;  worms,  45°-5O°  (tardigrades,  dried,  98°);  crus- 
taceans, 26°-43°;  insects,  270-43.;0;  fish,  2^-40°  ;  salamander, 
44°;  frog,  4O°-42°;  dog,  rabbit,  and  man,  44°-45°;  vertebrate 
muscle,  4O°-5O°.2  This  series  exhibits  a  wide  range  of  resistance 
to  excessive  heat,  yet  few  organisms  can  endure  much  above  50°. 

All  experiments  and  observations  indicate  that  death  from 
high  temperatures  is  caused  by  coagulation  of  the  albumen  of 
the  protoplasm,  a  circumstance  showing  that  albumen  carries 
into  its  vital  relations  its  ordinary  property  of  coagulation  by 
heat.  That  living  matter  contains  many  easily  coagulable  pro- 
teids  no  longer  admits  of  doubt,  and  that  their  coagulation  causes 
death  is  evidenced  by  the  fact  that  once  in  this  condition  they 
do  not  return  to  their  normal  state. 

1  C.  B.  Davenport,  Experimental  Morphology,  Part  I,  p.  232. 

2  For  full  tables  from  which  these  abstracts  are  made,  see  C.  B.  Davenport, 
Experimental  Morphology,  Part  I,  pp.  234-237. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION    261 

Death  from  low  temperatures  appears  to  result  from  entirely 
different  causes.  Protoplasm  seems  to  contain  no  substance  but 
water  that  undergoes  either  chemical  or  serious  physical  change 
by  low  temperatures.  Many  yeast  cells  endure  —  1 13.7°  C. 
(Schumacher). 

De  Candolle  subjected  "  various  dry  seeds  and  spores  of  bac- 
teria to  a  temperature  of  nearly  —  200°,  at  which  temperature  the 
atmosphere  becomes  liquefied,  but  without  fatal  effects."  "  Cilia 
from  the  mouth  of  the  frog  were  cooled  to  —  90°,  and  recovered 
their  movement  upon  raising  the  temperature."  "  Eggs  of  the 
frog,  lowered  slowly  to  —  60°,  can  revive."  From  facts  such  as 
these  Davenport  concludes  that  "there  is  no  fatal  temperature 
for  dry  protoplasm."  * 

The  first  effect  of  lowering  temperature  is  a  slowing  of  activity, 
followed,  finally,  by  complete  cessation.  As  is  pertinently  re- 
marked by  the  author  just  quoted,  "  The  fact  that  cold  rigor 
usually  occurs  close  to  the  zero  point  (C.)  indicates  that  the 
activities  of  protoplasms  are  closely  determined  by  the  fluid 
state  of  water,"  and  "  the  critical  point  for  vital  activity  has 
been  adjusted  to  this  critical  point  of  water."2 

There  is  much  lack  of  information  upon  the  exact  cause  of 
death  from  excessive  cold.  Among  the  higher  animals  the 
immediate  cause  is  without  doubt  asphyxia  from  the  cessation 
of  the  blood  flow  ;  but  among  the  simpler  organisms  the  matter 
is  not  so  clear.  What  evidence  we  have  seems  to  indicate  that 
the  primary  cause  of  death  is  in  all  probability  the  mechanical 
rupture  of  protoplasm  and  cell  wall  by  freezing  water  expanding 
as  it  solidifies. 

In  any  event  experience  and  experiment  agree  in  indicating 
that  protoplasm  is  resistant  to"  excessive  cold  in  the  absence  of 
moisture,  and  in  all  study  of  this  matter  we  are  to  remember 
two  facts  :  first,  that  the  freezing  point  of  all  protoplasm  is 
lower  than  that  of  water  only ;  and,  second,  that  as  long  as  the 
slightest  activity  is  present  heat  is  being  produced.  From  these 
two  facts  the  protoplasm  is  able  to  resist  actual  solidifying  much 

1  C.  B.  Davenport,  Experimental  Morphology,  Part  I,  pp.  240-242.    Though 
not  so  stated  in  the  text  quoted  these  temperatures  are  C. 

2  Ibid.  p.  242. 


262  CAUSES  OF  VARIATION 

longer  and  under  much  lower  temperatures  than  we  should  at 
first  suppose. 

Substantive  variation  due  to  temperature ;  color  markings. 
Early  in  the  section  it  was  remarked  that  the  effects  of  tem- 
perature are  qualitative  as  well  as  quantitative.  Without  doubt 
temperature  exerts  a  controlling  influence  upon  the  color  of 
butterflies,  as  has  been  determined  by  a  number  of  direct  ex- 
periments. 

For  example,  Vanessa  levana  and  V.prorsa  were  long  regarded 
as  distinct  species.  Levana  is  "characterized  by  a  yellow-and- 
black  pattern  on  the  upper  side  of  the  wings,"  while  prorsa 
"has  black  wings  with  a  broad  white  transverse  band  and  deli- 
cate yellow  lines  running  parallel  to  the  margins."1  Later  this 
was  recognized  as  a  case  of  "•'•-seasonal dimorphism"  the  yellow- 
and-black  levana  being  the  spring  brood  and  the  darker  prorsa 
being  the  summer  brood.;  that  is  to  say,  levana,  emerging  in 
the  spring,  breeds  immediately,  producing  a  summer  brood 
(prorsa))  and  this  brood  in  the  same  way  gives  rise  to  a  genera- 
tion which  passes  the  winter  in  the  chrysalis  form,  emerging  in 
the  spring  as  levana.  Thus  these  two  "  species  "  are  produced 
from  the  same  stock,  the  difference  being  that  one  passes  the 
chrysalis  stage  in  the  summer,  the  other  in  the  winter. 

That  this  difference  is  one  of  temperature  was  proved  by 
direct  experiment.  Dorfmeister  2  succeeded  in  producing  prorsa 
directly  irom  prorsa  by  the  application  of  warmth  to  the  pupae, 
and  "  by  the  application  of  cold  he  obtained  from  levana  not 
the  pure  levana  form,  but  one  intermediate  between  it  and 
prorsa!' — an  intermediate  occasionally  observed  in  nature  and 
known  as  V.  porima? 

Weismann,  repeating  the  experiment,  found  that  by  using 
lower  temperatures  levana  could  be  produced  directly  from 
levana,  and  he  adds,  "  The  converse  experiment  was  also  occa- 
sionally successful,  the  pupae  of  the  winter  generation  being 
forced  to  assume  the  summer  form  by  the  influence  of  a  higher 
temperature  during,  or  shortly  after,  pupation."  3 

1  Weismann,  Germ  Plasm,  p.  379. 

2  Vernon,  Variation  in  Animals  and  Plants,  p.  233. 

3  Ibid. ;  also  Weismann,  Germ  Plasm,  p.  379. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION    263 

Here  temperature  seems  to  exert  a  controlling  influence  upon 
pigment  formation,  although  Weismann  is  careful  to  inform  us  l 
that  the  two  patterns  "  do  not  correspond  "  ;  that  if  we  were  to 
''superpose"  one  upon  the  other,  "it  would  seem  that  the 
black  parts  in  prorsa  do  not  correspond  to  the  yellow  ones  in 
levana,  and  that  the  white  band  in  the  former  does  not  corre- 
spond to  [either]  a  yellow  or  [a]  black  part  in  the  latter.  This 
band  is,  on  the  contrary,  entirely  wanting  in  levana,  and  is 
represented  by  both  black  and  yellow  regions."  1 

Again,  Weismann  experimented  with  Polyommatus  phlceas? 
a  species  "distributed  over  the  whole  of  the  temperate  and 
colder  parts  of  Europe  and  Asia."  Toward  the  north  (in 
Germany)  the  upper  surface  of  the  wings  is  of  a  "  beautiful 
reddish-gold  color,"  hence  its  popular  name,  "  fire  butterfly." 
But  he  says,  "  Farther  south  the  reddish-gold  color  is  more  or 
less  thickly  dusted  with  black,  and  specimens  from  Sicily, 
Greece,  or  Japan  often  display  only  a  few  reddish-gold  scales, 
the  general  appearance  being  almost  black." 

"  In  Germany  this  butterfly  is  double-brooded,  and  the  two 
generations  are  similar,  but  in  certain  districts  of  southern 
Europe  .  .  .  the  first  generation  is  reddish-gold,  —  the  second, 
which  flies  in  midsummer  and  is  known  as  the  variety  eleus, 
having  the  wings  well  dusted  with  black."  "As  in  Germany 
during  exceptionally  hot  summers  individuals  with  a  blackish 
tint  have  repeatedly  been  caught  together  with  the  ordinary 
form  .  .  . ,"  and  Weismann  observes  that  it  would  seem  "  the 
butterfly  becomes  red  when  exposed  to  a  moderate  temperature 
and  black  when  the  heat  is  greater." 

Attempts  to  produce  these  forms  at  will,  however,  by  regula- 
tion of  temperature  only  partially  succeeded.  But  the  conditions 
were  severe.  There  was  no  common  ancestor.  Weismann  under- 
took to  produce  the  southern  form  from  the  northern  stock  and 
vice  versa.  Insects  reared  from  German  butterflies  but  kept  in 
high  temperatures  were  in  many  instances  "  dusted  with  black, 
but  none  of  them  resembled  the  darkest  forms  of  the  southern 
eleus"  Conversely,  butterflies  raised  in  cool  temperatures  from 

1  Weismann,  Germ  Plasm,  p.  379. 

2  Ibid.  pp.  399-400. 


264  CAUSES  OF  VARIATION 

Neapolitan  stock  were  lighter  in  color  than  in  their  native  habi- 
tat, but  "  none  were  so  light-colored  as  the  ordinary  German 
form."  l  This  difference  he  ascribes  to  the  cumulative  influence 
of  the  natural  seasonal  temperatures,  and  is  quick  to  protest 
against  its  interpretation  as  indicating  an  inheritance  of  acquired 
characters.  He  calls  it  a  case  of  internal  selection  as  between 
"winter  and  summer  determinants." 

However,  that  is  of  no  consequence  in  the  present  connection. 
The  facts  here  given  show  beyond  a  doubt  that  outside  tempera- 
tures exert  a  direct  effect  upon  so  important  a  character  as 
color.  Whether  this  occurs  by  chemical  disturbance  in  pigment 
formation,  by  internal  selection,  or  by  other  means  does  not 
greatly  matter  here.  There  is  some  evidence  tending  to  show 
that  the  light  color  of  polar  animals  is  due  to  the  direct  action 
of  cold.2  This,  if  true,  argues  for  chemical  action  upon  pigment 
as  the  cause  of  color  changes  due  to  temperature. 

Temperature  an  all-pervading  influence.  Temperature  differs 
from  most  other  external  forces  in  being,  for  many  species,  at 
least,  an  all-pervading  influence.  Higher  animals  and  plants 
are  themselves  centers  of  heat  production,  and  in  general  their 
temperatures  are  the  algebraic  sum  of  their  own  heat  production 
and  the  heat  of  their  surroundings.  Lower  organisms,  however, 
are  very  largely  dependent  upon  their  environment  for  their 
temperatures,  and  in  cases  of  this  kind  the  entire  protoplasm  of 
the  body  is  affected. 

SECTION  VIII  — EFFECT  OF  CHEMICAL  AGENTS  UPON 
PROTOPLASMIC  ACTIVITY 

All  development,  all  differentiation,  and  all  functional  activity 
of  living  organisms  are  the  result  of  protoplasmic  activity ;  but 
protoplasmic  activity  is,  in  the  last  analysis,  chemical  activity, 
and  it  is  certainly  subject  to  many  of  the  laws  controlling  ordi- 
nary chemical  reactions.  It  is  noticeable  in  the  study  of  vital 

1  Weismann,  Germ  Plasm,  pp.  399-400. 

2  The  writer  has  somewhere  read  that  animals  on  shipboard  become  rapidly 
lighter  in  color  as  the  coat  becomes  exposed  to  intense  cold,  but  he  is  unable  to 
verify  the  report. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION    265 

processes  from  the  chemical  standpoint  that  some  substances 
exert  no  influence  upon  protoplasm,  while  others  kill  it  out- 
right ;  that  some  accelerate  and  others  retard  its  normal  action ; 
and  that  some  suspend  activities  more  or  less  completely,  while 
others  divert  them  into  entirely  new  channels.  Here  is  varia- 
tion due  to  chemical  disturbance  of  the  material  basis  of  life, 
and  it  is  well  to  study  somewhat  in  detail  this  "  modification  of 
vital  actions  "  from  chemical  causes.1  In  studying  this  class  of 
phenomena  it  is  necessary,  of  course,  to  make  use  of  simple 
organisms  of  one  or  of  few  cells,  and  while  we  cannot  reason 
directly  from  these  to  the  higher  animals  and  plants,  still  all 
evidence  goes  to  show  that  the  differences- are  not  so  much  in 
kind  as  in  complexity. 

Oxygen.  All  experiments  indicate  that  no  protoplasm  can 
long  survive  in  the  absence  of  oxygen.  In  most  cases  it  is  taken 
directly  from  the  air,  but  in  others,  as  in  anaerobic  bacteria,  it 
is  probably  extracted  from  surrounding  compounds  containing 
oxygen.  Diminished  oxygen  retards  and  increased  oxygen  and 
ozone  greatly  accelerate  the  vital  processes,2  all  without  chang- 
ing their  character. 

A  number  of  oxygen-containing  substances  greatly  retard  or 
even  destroy  vital  activities,  probably  through  "  oxidation  of  the 
protoplasm."3  If  this  be  the  case,  and  the  material  basis  of 
life  is  subject  to  the  ordinary  chemical  process  of  oxidation,  it 
shows  that  vital  processes  in  the  last  analysis  rest  upon  a  strong 
chemical  basis. 

Hydrogen  peroxide  (H2O2),  only  slightly  different  from  water 
(H2O),  is  a  powerful  oxidizing  agent.  One  part  in  ten  thousand 
(o.o  i  per  cent)  in  hay  infusion  killed  all  ciliata  in  from  fifteen  to 
thirty  minutes.  Algae  survived  a  o.  I  per  cent  solution  but  ten 
or  twelve  hours,  and  died  in  a  10  per  cent  solution  in  a  few 
minutes.  "  Salts  of  chromic,  manganic,  permanganic,  and  hypo- 
chlorous  acids  act  as  intense  poisons,  apparently  by  directly  yield- 
ing oxygen  atoms  to  the  plasma  proteins."  Chlorin,  iodin,  and 

1  C.  B.  Davenport,  Experimental  Morphology,  Part  I,  chap,  i,  from  which  the 
data  in  this  section  are  largely  taken. 

2  Small  animals  confined  in  an  atmosphere  of  pure  oxygen  exhibit  greatly 
increased  activity  and  "  live  themselves  to  death  "  in  a  few  hours. 

3  C.  B.  Davenport,  Experimental  Morphology,  Part  T,  p.  3. 


266  CAUSES  OF  VARIATION 

bromin  in  the  presence  of  water  act  "  fatally  upon  all  organisms 
by  splitting  [the]  water,  forming  hydro-halogen  compounds,  and 
leaving  the  oxygen  to  unite  with  the  living  protoplasm."  1 

Hydrogen.  Amoebae  subjected  to  an  atmosphere  of  hydrogen 
for  twenty-four  minutes  became  motionless,  some  having  assumed 
the  spherical  form.  The  same  general  result  followed  in  trades- 
cantia  hairs,  but  from  the  fact  that  normal  activity  was  restored 
by  admitting  air  it  was  assumed  that  the  results  arose  not  from 
any  injurious  effect  of  hydrogen  but  from  the  exclusion  of  oxygen.2 

Oxids  of  carbon,  —  C02  and  CO.  These  two  oxids  of  carbon 
have  very  different  effects  upon  protoplasm.  The  former,  like 
hydrogen,  seems  to  act  only  by  excluding  oxygen,  death,  when 
it  results,  being  due  mainly  to  asphyxia,  while  the  latter  kills  by 
attacking  the  protoplasm  directly.3 

Catalytic  poisons.4  A  large  number  of  unstable  carbon  com- 
pounds, neither  acid  nor  basic  and  therefore  not  characterized 
by  intense  chemical  action,  are  yet  violent  poisons.  Here  belong 
the  anaesthetics,  as  chloroform,  chloral,  ethyl  ether,  alcohols,  etc. 

These  unstable  compounds  are  characterized  by  a  "  lively 
condition  of  molecular  movement  "  (Nageli),  which  is  considered 
to  disturb  the  normal  movements  of  the  protoplasm,  or  "to 
lead  to  chemical  transformations  in  the  unstable  albumen  of  the 
protoplasm"  (Loew). 

Catalytic  substances  are  supposed  to  exert  their  action  not  by 
entering  into  and  effecting  new  combinations  but  by  disturbing, 
through  their  mere  presence,  the  usual  behavior  of  bodies.  It 
is  in  this  way  that  protoplasm  suffers  in  their  presence.  Thus 
hydrochloric  and  prussic  acids  unite  only  at  high  temperatures, 
except  in  the  presence  of  various  ethers,  when  they  will  unite 
even  at  —  15°.  The  vigor  of  this  catalytic  action  is  in  proportion 
to  the  molecular  composition.5  Thus  in  the  methan  series  with 
CH3  as  the  base  we  have  CH4,  C2H6,  C3H8,  etc.,  in  which 

1  C.  B.  Davenport,  Experimental  Morphology,  Part  I,  p.  4. 
8  Ibid.  p.  5. 

3  Ibid.  p.  6. 

4  A  free  extract  from  C.  B,  Davenport,   Experimental   Morphology,   Part   I, 
pp.  7.  8. 

6  The  facts  here  stated  are  taken  almost  literally  from  C.  B.  Davenport, 
Experimental  Morphology,  Part  I,  pp.  7-8. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION    267 

"  the  poisonous  action  increases  up  to  a  certain  limit  in  proportion 
to  the  number  of  C  atoms"  while  "  above  this  limit  the  com- 
pounds are  more  stable  and  are  more  indifferent,  as  for  example 
paraffin  (C21H44  to  C27H56).". 

Again,  in  such  a  series,  if  the  H  atoms  become  replaced  by 
one  of  the  halogens,  the  poisonous  properties  correspondingly 
increase ;  thus  : * 

CH4,  marsh  gas,  innocuous. 

CH3C1,  slightly  anaesthetic. 

CHC13,  chloroform,  powerful  anaesthetic. 

CC14,  very  dangerous,  stupefying  involuntary  muscles. 

Chloroform  and  etber  affect  all  protoplasm,  both  plant  and 
animal,  higher  as  well  as  lower.  They  seem  to  produce  at  first 
(two  to  five  minutes  in  a  25  per  cent  water  solution)  a  "  very 
intense  excitement  in  the  movement  of  the  protoplasm,"  fol- 
lowed by  "  strong  vacuolization,  and  then  the  cytoplasm  grad- 
ually becomes  immobile  "  and  dies,  if  the  influence  is  continued. 
In  a  similar  way  the  various  alcohols  exert  stupefying  effects  in 
proportion  to  the  number  of  CH2  radicals  present,  and  carbon 
disulphid  (CS2)  is  one  of  the  most  powerful  catalytic  poisons. 

OProtoplasm  is  therefore  subject  to  catalytic  disturbances,  in 
which  it  is  not  different  from  other  and  more  ordinary  chemical 
materials, — a  fact  in  itself  exceedingly  significant  to  the  stu- 
dent looking  for  fundamental  causes  of  variation. 

Poisons  which  form  salts.2  These  are  acids  and  bases  which 
Loew  believes,  as  stated  by  Davenport,  "unite  [directly]  with 
the  protein  substances  of  the  protoplasm,  producing  salts," 
disturbances  that  of  course  soon  lead  to  death.  Thus  "  formic 
acid,  even  in  small  per  cents,  —  0.05  per  cent  to  0.006  per  cent, 
—  prevents  the  development  of  bacteria.  On  the  other  hand, 
some  protoplasm  has  acquired  a  resistance  to  organic  acids,  the 
vinegar  eel  living  in  4  per  cent  acetic  acid,"  and  the  gland  cells 
of  some  marine  Gastropoda  secrete  from  2  per  cent  to  3  per 
cent  of  H2SO4,  a  strength  which  is  fatal  to  most  protoplasm. 

1  The  halogens  —  fluorin,  chlorin,  bromin,  and  iodin  — form  a  group  of  sub- 
stances of  very  similar  chemical  properties,  but  form,  in  the  order  named,  a 
decreasing  series  as  to  chemical  energy. 

2  C.  B.  Davenport,  Experimental  Morphology,  Part  I,  pp.  12-14. 


268  CAUSES  OF  VARIATION 

Nageli's  experiments :  indicate  that  water  distilled  in  cop- 
per vessels,  or  standing  four  days  in  other  vessels  with  twelve 
clean  copper  coins  per  each  liter  of  water,  was  fatal  to  Spiro- 
gyra,  though  the  proportion  of  copper  to  water  was  but  i  to 
77,000,000. 

These  reactions,  resulting  in  death  rather  than  in  modified 
action,  are  important,  not  as  showing  primary  causes  of  varia- 
bility but  as  proving  again  that  living  protoplasm  is  still  subject 
to  many  of  the  chemical  affinities  that  controlled  its  elements 
before  they  became  organized  into  living  matter.  It  must  be 
remembered  in  this  connection  that  many  of  these  substances 
attack  only  living  protoplasm,  having  no  action  upon  dead  pro- 
toplasm, showing  that  at  death  the  highly  complex  materials 
have,  to  some  extent  at  least,  broken  down. 

The  action  of  some  poisons,  like  nicotin,  is  proportional  to 
the  "  differentiation  of  nervous  substance  "  ;  others,  like  cocain 
and  atropin,  first  excite  and  then  paralyze  the  central  nervous 
system  of  vertebrates,  but  act  as  violent  poisons  upon  undiffer- 
entiated  protoplasm  (Protozoa).2 

Toxic  poisons.  It  is  not  the  germ  that  kills,  but  rather  its 
specific  toxin  that  deranges  some  of  the  vital  functions  beyond 
endurance.  The  dire  effects  of  germ  diseases  are  therefore  due 
not  so  much  to  the  organisms  themselves  as  to  their  constant 
manufacture  within  the  body  of  a  chemical  poison  which  the 
protoplasm  cannot  endure  and  preserve  its  normal  functions.  It 
may  die  in  the  attempt,  or  it  may  succeed  and  become  accli- 
mated, but  while  the  struggle  is  on,  the  body  functions  will  be 
considerably  disturbed.  It  is  significant  that  compounds  similar 
to  those  of  disease-producing  bacteria  have  been  "  extracted  from 
the  seeds  of  some  phanerogams  ;  for  example,  ricin  from  the  seeds 
of  the  castor-oil  bean,  etc."  In  this  class  may  come  the  poisons 
secreted  by  certain  animals,  as  the  rattlesnake  and  cobra,  fatal 
to  vertebrates  but  innocuous  to  Infusoria  and  Flagellata. 

It  is  also  noteworthy  that  the  blood  serum  of  one  species 
rapidly  dissolves  the  corpuscles  of  another  (red  and  white),  and 
is  therefore  injurious  or  fatal  according  to  the  amounts  present.3 

1  C.  I*.  Davenport,  Experimental  Morphology,  Part  I,  p.  14. 

2  Ibid.  pp.  23  and  24.  3  ibid.  p.  22. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION    269 

Specific  secretions  and  glandular  activity.  The  fact  just  men- 
tioned introduces  a  subject  full  of  interest.  It  appears  that  each 
species,  and  perhaps  each  individual,  is  engaged  in  the  produc- 
tion of  chemical  substances  (whether  the  result  of  anabolic  or 
katabolic  activity  is  uncertain)  which  exert  specific  action  upon 
living  matter. 

It  is  significant  that  some  of  the  lower  organisms  producing 
definite  substances  die  from  the  injurious  effects  of  their  own 
product,1  unless  this  is  removed  as  formed,  and  that  higher  ani- 
mals are  supplied  with  elaborate  excreting  apparatus,  strongly 
suggesting  that  certain  of  their  products  are  deleterious  to  the 
organisms  that  produced  them,  while  in  other  cases  they  are 
clearly  beneficial.  In  this  connection  Loeb  remarks  : 2 

It  is  perhaps  not  impossible  that  those  mental  diseases  that  are  heredi- 
tary are,  in  reality,  chemical  diseases  caused  by  poisons  that  are  formed 
in  the  body,  just  as  special  substances — for  instance,  alcohol,  hashish, 
and  other  intoxicating  substances  —  produce  temporary  mental  diseases. 
The  delirium  of  fever,  as  well  as  certain  other  mental  diseases,  may  owe 
their  origin  to  poisons  which  are  formed  in  the  body.  It  is  quite  possible 
that  these  poisons  are  also  formed  in  the  normal  body.  It  is  only  necessary 
that  they  be  formed  in  somewhat  larger  quantities  or  destroyed  in  some- 
what smaller  quantities  in  the  body  of  the  insane  than  in  the  normal  man.3 

It  is  further  not  at  all  necessary  that  the  hypothetical  poisons  which 
cause  mental  diseases  be  formed  in  the  central  nervous  system.  They  may 
be  formed  in  any  organ  of  the  body.  It  is  only  necessary  that  they  affect 
the  central  nervous  system  ;  in  other  words,  that  they  be  nerve  poisons. 

Nothing  is  better  qualified  to  make  this  view  clear  than  the  result  which 
the  destruction  of  the  thyroid  gland  has  on  the  mental  and  physical  devel- 
opment of  children.  We  know  that  in  case  of  degeneration  of  the  thyroid 
gland  the  growth  and  mental  development  of  the  child  are  retarded.  Idiocy 
may  result  from  the  destruction  of  the  thyroid  gland.  It  has  been  found 
that  an  improvement,  or  even  a  cure,  can  be  attained  by  feeding  patients 
afflicted  with  this  trouble  with  the  thyroid  substance  of  animals.4  Baumann 
found  that  the  thyroid  gland  contains  an  element  which  is  contained  in  no 
other  organ  of  the  body,  —  namely,  iodin. 

1  The  yeast  plant  that  forms  alcohol  dies  when  the  solution  has  reached  a 
strength  of  about  20  per  cent. 

2  Loeb,  Physiology  of  the  Brain,  p.  207. 

3  It  is  said  by  Lombroso,  and  others  agree,  that  the  criminal  is  characterized 
by  excessive  amounts  of  urea. 

*  Medicinal  preparations  from  various  glands  are  now  regularly  supplied  by 
the  large  slaughterhouses, 


270  CAUSES  OF  VARIATION 

Insect  poisons.  The  poison  of  bees  —  formic  acid  —  is  fata] 
to  insects  and  small  animals,  and  in  sufficient  quantity  to  the 
larger  vertebrates,  including  man,  though  frequent  stings  of  a 
moderate  number  lead  rapidly  to  acclimatization.  It  is  note- 
worthy, too,  in  this  connection  that  the  sting  of  the  insect 
(mud  wasp,  for  example)  does  not  always  kill  but  often  merely 
paralyzes,  so  that  the  creature  stored  with  the  egg  will  remain 
alive  to  furnish  food  to  the  larvae  some  weeks  later. 

Galls.  Galls  are  the  direct  result  of  the  sting  of  an  insect, 
leaving  a  specific  poison  to  act  upon  a  particular  form  of  proto- 
plasm. The  result  is  not  death  but  a  diverting  of  the  activities 
into  entirely  new  channels.  Darwin  states  that  "  no  less  than 
fifty-eight  kinds  of  gall  are  produced  on  the  several  species  of 
oaks  by  Cynips  with  its  sub-genera,  and  Mr.  B.  D.  Walsh  states 
that  he  can  add  many  more."  l 

Darwin  further  remarks  that  many  gall  insects  are  exceedingly 
small,  and  that  consequently  the  drop  of  poison  they  inject  must 
be  exceedingly  minute ;  moreover,  it  is  never  injected  but  once. 
The  growth  that  follows,  however,  is  specific  and  continuous. 
He  quotes  Walsh  as  saying,  "  Galls  afford  good,  constant,  and 
definite  characters,  each  kind  keeping  as  true  to  form  as  does 
any  independent  organic  being,"  2  and  he  calls  our  attention  to 
the  fact  that  seven  of  the  ten  distinctly  different  galls  produced 
on  the  willow  are  by  insects  which,  "  though  essentially  distinct 
species,  yet  resemble  one  another  so  closely  that  in  almost  all 
cases  it  is  difficult  and  in  most  cases  impossible  to  distinguish 
the  full-grown  insects  one  from  another."  The  difference  in  the 
quality  of  the  poison  secreted  by  insects  so  nearly  alike  cannot  be 
great,  yet  it  is  sufficient  to  give  rise  to  galls  widely  different. 
Last,  and  not  least,  he  mentions  that  "  Cynips  fecundatrix  has 
been  known  to  produce  in  the  Turkish  oak,  to  which  it  is  not 
properly  attached,  exactly  the  same  kind  of  gall  as  on  the 
European  oak.  These  latter  facts  apparently  prove  that  the 
nature  of  the  poison  is  a  more  powerful  agent  in  determining 
the  form  of  the  gall  than  [is]  the  specific  character  of  the  tree 
which  is  acted  on."* 

1  Darwin,  Animals  and  Plants,  II,  272.  2  Ibid.  p.  273. 

a  We  know  now  that  the  gall  does  not  develop  unless  the  egg  hatches. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION    271 

Tumors.  Those  overgrowths  of  various  parts  of  the  body, 
called  tumors,  arising  from  causes  not  well  understood,  have 
their  specific  characters  as  truly  as  if  derived  from  inherit- 
ance. Whether  the  character  of  the  tumor  is  derived  primarily 
from  the  tissues  affected  or  from  some  outside  specific  cause  is 
not  known,  but  it  is  a  significant  fact  that  the  protoplasm,  which 
derived  its  characters  originally  by  inheritance,  has  undergone 
permanent  and  definite  alteration  through  the  operation  of  causes 
absolutely  distinct  from  inheritance,  whether  internal  or  external 
to  the  organism,  thus  showing  the  possibility  of  diverting  the  ener- 
gies of  inherited  material  into  absolutely  new  channels  through 
apparently  slight  causes. 

At  this  point  it  is  well  to  call  our  attention  to  the  profound 
changes  (permanent  variations)  wrought  upon  the  constitution 
of  the  individual  by  such  internal-external  circumstances  as  vacci- 
nation or  the  injection  of  antitoxin,  as  well  as  to  the  immunity 
acquired  through  a  single  attack  of  an  infectious  disease. 

Germination  of  seeds.  It  is  a  well-known  fact  that  certain 
chemicals  accelerate  and  others  retard  the  process  of  germina- 
tion. Just  why  this  is  true  is  not  clear  on  any  other  ground 
than  that  of  the  ordinary  susceptibility  of  growing  protoplasm 
to  stimulants  and  sedatives.  The  process  of  germ  development 
requires,  in  addition  to  what  is  contained  within  the  seed,  only 
oxygen,  water,  and  a  favorable  temperature ;  the  influence  of 
other  chemicals  must  be  indirect. 

Chemotaxis  and  chemotropism.1  The  influence  of  chemical 
substances  upon  the  locomotion  of  free-moving  organisms  is  tech- 
nically known  as  chemotaxis,  and  their  influence  upon  the  direc- 
tion of  growth  (in  plants)  is  known  as  chemotropism.2  The 
distinction  is  hardly  worth  observing  for  our  purposes,  because 
both  phenomena  arise  from  a  direct  influence  of  chemical  sub- 
stances upon  living  protoplasm,  either  attractive  or  repellent.  If 
attractive,  it  (the  protoplasm)  will  move  toward  the  material  in 

1  C.   B.   Davenport,  Experimental  Morphology,  Part  I,  32-45  ;  Part  II,  pp. 
335-342;  Loeb,  Physiology  of  the  Brain,  pp.  50,  88-90,  118,  186-188. 

2  As  has  already  been  noted,  the  same  distinction  is  often  observed  between 
geotaxis,  the  influence  of  gravity  upon  locomotion,  and  geotropism,  its  influence 
upon  the  direction  of  growth ;  also  between  heliotaxis  and  heliotropism  as  cover- 
ing corresponding  influences  of  the  sun  (light). 


272  CAUSES  OF  VARIATION 

question,  providing  it  is  free  to  do  so  (as  in  the  case  of  the 
lower  plants  and  all  animals),  or  its  growth  will  be  directed 
toward  it  if  (as  in  the  case  of  higher  plants)  it  is  fixed  and  un- 
able to  move.  The  former  is,  strictly  speaking,  chemotaxis  ;  the 
latter  is  chemotropism.  For  our  purposes  it  is  a  distinction 
without  a  difference,  because  in  the  latter  case  the  plant  is 
unable  to  indulge  in  locomotion,  and  performs  the  nearest  pos- 
sible act  in  changing  the  direction  of  growth.  Both  are  loco- 
motion under  the  circumstances ;  both  are  due  to  the  same 
cause,  —  a  chemical  affinity  or  attraction,  —  and  they  differ 
because  of  differences  in  the  organisms  affected  in  respect  to 
the  power  of  locomotion,  not  because  of  differences  in  the  nature 
of  the  forces  in  action.  The  two  terms  are,  therefore,  for  our 
purposes,  synonymous  as  denoting  a  power  of  attraction  between 
protoplasm  and  certain  ordinary  chemical  compounds  such  as  to 
cause  the  protoplasm  to  approach  if  it  be  free  to  move,  or,  if  not, 
to  grow  in  that  direction,  —  which  is  all  that  can  be  done  under 
the  circumstances  to  satisfy  the  affinity. 

Chemotaxis,  or  chemotropism  as  the  writer  prefers  to  call 
it,1  has  but  a  slender  hold  upon  higher  animals.  It  appears  to 
be  localized  in  the  nostrils  and  to  manifest  itself  only  in  the 
sense  of  smell,  agreeable  or  otherwise ;  but  in  lower  organisms, 
even  in  many  insects,  it  is  apparently  not  confined  to  a  minute 
fraction  of  the  surface,  but  pervades  the  whole  organism  with 
an  influence  that  is  all  but  overpowering.  It  may  of  course  be 
aided  or  opposed  by  other  tropisms,  as  gravity  or  light,  in  which 
case  the  total  result  is  the  algebraic  sum  of  all  the  energies 
operative,  but  that  chemotropism  is  a  force  to  be  reckoned  with 
in  development  is  a  fact  not  to  be  doubted. 

Examples  of  chemotropism.2  Englemann  noticed  that  bac- 
teria under  a  cover  glass  will  gather  along  the  margin,  or  if 
green  algae  be  introduced  they  will  cluster  about  them  so  long 
as  they  are  producing  oxygen,  but  in  the  darkness  they  will  not 

1  The  ending  "  taxis  "  is  from  the  Greek,  meaning  assortment  or  arrangement ; 
the  ending  "  tropism  "  is  from  "  tropic,"  to  turn.    "  Chemotropism  "  is  pronounced 
ke"-mot'r6"-pizm. 

2  Until  otherwise  noted  what  follows  is  a  free  though  not  exact  transcript  from 
data  given  in  C.  B.  Davenport's  Experimental  Morphology,  Part  I,  pp.  32-39. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION 


273 


be  affected.  In  the  same  way  nearly  all  kinds  of  motile  organ- 
isms are  now  known  to  be  influenced  by  a  variety  of  chemical 
substances. 

Lubbock  has  shown  that  ants  retreat  from  essence  of  clove, 
lavender  water,  etc.,1  placed  within  one  fourth  inch  of  their 
path,  and  Loeb  found  that  the  larvae  of  flies  creep  towards  a 
piece  of  flesh  brought  nearer  than  1.5  cm.  Not  only  flesh  and 
decaying  meat,  but  meat  juice  in  a  glass,  will  allure,  while  fat 
has  no  effect.  Every  farmer  knows  how  quickly  flies  are 
attracted  by  a  dressed  animal,  and  carrion  birds  by  a  carcass. 

According  to  Pfeffer's  experiments  the  inorganic  salts  of 
potassium,  sodium,  calcium,  ammonium,  magnesium,  and  many 
other  metals  in  0.5  per  cent  solution  act  attractively  upon  Bac- 
terium termo.  "  Inorganic  acids  ...  in  general  act  repulsively," 
but  phosphoric  acid  and  the  phosphates  are  strongly  attractive. 
Dewitz  states  that  mammalian  spermatozoa  are  attracted  by 
KOH. 

"  Alcohol  in  grades  between  10  per  cent  and  i  per  cent  acts 
repulsively  towards  bacteria,"  but  "glycerin  is  neutral."   Malic 
acid,  which  is  of  wide  distribution  among  plants,  is  strongly 
attractive  to  spermatozoids,  even  in  a  o.ooi  per  cent  solution,  - 
a  fact  which  is  highly  significant. 

This  principle  of  chemotropism  acting  on  higher  organisms 
gives  rise  to  characteristic  movements.  In  Loeb's  experiments 
on  actinians  2  a  piece  of  meat  laid  upon  the  tentacles  so  affected 
them  as  to  cause  a  bending  which  carried  the  meat  into  the 
mouth,  while  a  wad  of  water-soaked  paper  had  no  effect,  but  lay 
there  until  removed.  If,  however,  the  paper  was  soaked  in  meat 
juice  it  was  received  the  same  as  a  piece  of  real  meat.  (See 
Fig.  29.) 

Now  the  actinian,  consisting  simply  of  a  sac  with  a  row  of 
tentacles  around  the  edge,  without  brain  or  nerve  centers  of 

1  Experimenting  upon  means  of  preventing  the  ravages  of  the  corn-root  aphis, 
Forbes  of  Illinois  found  that  a  small  amount  of  oil  of  lemon  on  the  seed  corn, 
before  planting  (costing  but  ten  cents  per  acre),  is  able  by  its  strong  odor  to 
repel  ants  from  the  neighborhood  of  the  corn  hill  for  no  less  than  six  weeks 
after  planting.     As  the  young  aphis  is  absolutely  dependent  upon  the  attentions 
of  the  ant,  this  treatment  is  effective. 

2  Loeb,  Physiology  of  the  Brain,  pp.  49-50: 


274 


CAUSES  OF  VARIATION 


any  kind,  is  certainly  incapable  of  exercising  anything  like  in- 
telligent choice.  The  characteristic  movement  must  have  been 
due  to  the  specific  chemical  action  of  the  juices  of  the  meat 
upon  the  protoplasm  of  the  muscle  fibers  of  the  tentacle,  while 
the  paper  had  no  such  action  and  hence  no  movement  followed. 
This  movement  and  non-movement  look  like  intelligence  or 

instinct  and  have  often 
passed  for  one  or  the 
other  to  the  infinite  con- 
fusion of  the  subject.1 

" Lumbrici  fcetidi  live 
in  the  decaying  compost 
of  old  stables,  and  prob- 
ably the  chemical  nature 
of  certain  sub- 
==    stances  con- 
tained in  the 
compost  holds 
them   there," 

FIG.  29.   Stimulating  effect  of  certain  chemicals  upon  mus-     for  "when  one 
cular  action :  a  piece  of  meat  laid  upon  the  tentacles  of     h  ajf     of     the 


the  actinian  stimulates  their  action  and  it  is  drawn  into  the 
mouth.    A  piece  of  paper  similarly  placed  is  inoperative 


bottom  of    the 
box  is  covered 

with  moist  blotting  paper  and  the  other  half  with  a  thin  layer 
of  compost,  all  the  worms  will  gather  on  the  compost  side." 
Decapitated  worms  behave  in  the  same  way,2  so  that  the 
effect  is  due  to  a  general  influence,  not  to  "  nerve  centers." 
Loeb  says,3  "  I  have  often  placed  pieces  of  lean  meat  and 
pieces  of  fat  from  the  same  animal  side  by  side  on  the  window 
sill,  but  the  fly  never  failed  to  lay  its  eggs  on  the  meat  and  not 
on  the  fat."  (He  tried,  of  course  without  success,  to  raise  larvae 
in  the  fat.)  "  It  can  easily  be  shown  that  larvae  of  the  fly  are  posi- 
tively chemotropic  towards  certain  chemical  substances  which 
are  formed,  for  instance,  in  decaying  meat  or  cheese,  but  which 
are  not  formed  in  fat.  The  substances  in  question  are  probably 
volatile  nitrogenous  compounds,"  and  "  the  chemical  effects  of 

1  This  subject  will  be  pursued  further  under  "  Instinct  and  Reflex  Action." 

2  Loeb,  Physiology  of  the  Brain,  p.  90.  8  Ibid.  pp.  186-187. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION    275 

the  diffusing  molecules  on  certain  elements  of  the  skin  influence 
the  tension  of  the  muscles,"  causing  motion. 

The  female  fly  is  attracted  by  meat,  the  same  as  are  larvae,  and 
"  as  soon  as  the  fly  is  seated  on  the  meat  chemical  stimuli  seem 
to  throw  into  activity  the  muscles  of  the  sexual  organs,  and 
eggs  are  deposited  on  the  meat."  This  chemical  stimulus  is 
about  all  there  is  of  the  wonderful  "  instinct"  by  which  insects 
are  led  "  always  to  deposit  their  eggs  in  exactly  the  right  places." 

These  and  similar  examples  show  the  effect  of  certain  chem- 
icals upon  free-moving  organisms.  It  remains  to  illustrate  their 
effect  upon  the  direction  of  growth  among  plants,  which  are  not 
free  to  move. 

First  of  all,  we  are  to  note  the  effect  of  certain  chemicals  upon 
the  tentacles  of  insectivorous  plants.  Darwin  noticed  that  "  when 
drops  of  water  or  solutions  of  non-nitrogenous  compounds  are 
placed  upon  the  leaves  of  the  sundew,  Drosera,  the  tentacles 
remain  uninflected  ;  but  when  a  drop  of  a  nitrogenous  fluid,  such 
as  milk,  wine,  albumen,  infusion  of  raw  meat,  saliva,  or  isinglass 
is  placed  on  the  leaf,  the  tentacles  quickly  bend  inwards  over 
the  drop."1  Darwin  found  that  of  "  nine  salts  of  ammonia  tried, 
all  caused  inflection,  and  of  these  the  phosphate  was  the  most 
powerful,"  and  that  "  sodium  salts  in  general  caused  inflection 
with  extreme  quickness."  This  action  of  nitrogenous,  phos- 
phatic,  and  other  chemicals  common  to  animal  life,  was  the 
same  upon  the  tentacles  of  insectivorous  plants  as  upon  the 
tentacles  of  lower  animals  subsisting  upon  the  same  kind  of 
food.2  Thus  plant  and  animal  tissues  appear  to  be  subject  to 
the  same  general  laws  in  this  regard. 

From  this  point  of  departure,  common  to  both  plant  and  ani- 
mal, we  note  that  the  animal,  free  to  move,  does  so  in  response 
to  this  class  of  stimuli.  What  does  the  plant  do  that  cannot 
move,  even  as  tentacles  move  ?  In  other  words,  how  does  chemot- 
ropism  affect  the  direction  of  growth  among  higher  plants  ? 

Roots  in  general  are  supposed  to  grow  toward  oxygen,  and 
pollen  tubes  will  certainly  turn  toward  the  stigma  of  the  flower, 

1  C.  B.  Davenport,  Experimental  Morphology,  pp.  335-336. 

2  See  the  experiment  on  actinians  previously  quoted  from  Loeb,  Physiology  of 
the  Brain,  pp.  49—50. 


276  CAUSES  OF  VARIATION 

the  supposition  being  that  sugar  is  the  special  .attracting  sub- 
stance in  the  latter  case.  It  is  noteworthy  that  the  pollen  tube 
is  attracted  not  simply  to  its  own  stigma  but  also  to  the  pistil 
and  the  ovule  of  other  species,  even  of  a  different  genus  with 
which  it  is  unable  to  unite.1  Davenport  says  : 2 

The  results  of  experimentation  upon  chemotropism  show  that  various 
substances  may  direct  the  growth  of  such  elongated  organs  as  tendrils,  roots, 
and  hyphae  of  plants.  ...  In  many  instances  it  can  be  shown  that  the 
direction  of  growth  is  on  the  whole  advantageous  to  the  organism.  ...  In 
other  cases,  however,  the  response  seems  to  have  no  relation  to  adaptation. 

The  immediate  cause  of  change  of  direction  is  "  excessive 
growth  on  one  side,  due  to  excessive  imbibition  or  to  excessive 
or  restricted  assimilative  activity." 

The  evidence  seems  conclusive  that  the  chemical  elements 
constituting  living  matter  have  not  entirely  lost  their  ordinary 
affinities  and  properties  ;  that  protoplasm  is  in  many  respects 
subject  to  the  laws  of  other  chemical  compounds ;  that  its  activ- 
ities may  be  accelerated  or  retarded ;  that  they  may  be  tempo- 
rarily or  even  permanently  modified  in.  character  by  chemical 
alteration,  or  even  entirely  destroyed  by  entering  into  new  and 
strange  combinations  with  surrounding  substances.  Here  is  a 
real  cause,  at  least  of  occasional  variation,  —  possibly  of  those 
sudden  changes  we  call  mutation. 

Rhythmical  contraction  of  muscle  instituted  by  certain  chem- 
ical substances.  The  irritability  and  consequent  contraction  of 
muscles  due  to  influences  of  a  chemical  nature  have  already  been 
noticed,  as  in  the  case  of  the  movement  of  the  tentacles  of  the 
actinian,  the  attractive  or  repulsive  effect  of  certain  odors,  and, 
to  some  extent,  in  the  placing  of  insect  eggs  in  "  exactly  the 
right  spot." 

It  is  now  well  known  that  certain  salts  exert  a  specific  action 
upon  muscle,  exciting  even  rhythmic  contraction.  As  long  ago 
as  1 88 1  Biedermann  discovered  that  if  the  muscle  of  a  frog  be 
carefully  excised  at  a  low  temperature  (o°-io°  C.),  then  weighted 
and  dipped  into  a  0.6  per  cent  solution  of  sodium  chlorid  con- 
taining also  small  amounts  of  sodium  phosphate  and  sodium 

1  C.  B.  Davenport,  Experimental  Morphology,  p.  339.          2  Ibid.  p.  343. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION     277 

carbonate  "one  observes  as  a  rule,  after  a  longer  or  shorter  period 
of  rest,  that  the  immersed  muscle  begins  to  beat  rhythmically'' 

On  this  point  Loeb  remarks  that  sometimes  only  a  mere 
tremor  is  noticeable,  at  others  violent  contractions  ;  that  some- 
times only  individual  fibers  are  active,  at  others  the  whole  muscle 
is  involved;  and  that  "at  low  temperatures  these  phenomena 
may  continue  for  days."  1 

These  facts,  together  with  Ringer's  and  Howell's  statements 
that  calcium  and  potassium  salts  exert  a  direct  action  upon  the 
heart,  led  Loeb  to  extend  the  Biedermann  investigations.  He 
subjected  the  gastrocnemius  muscle  of  a  frog  (unweighted)  to  a 
series  of  solutions  of  chemically  pure  materials  in  twice-distilled 
water.2 

These  experiments  not  only  confirmed  Biedermann's  findings 
that  the  salts  of  sodium  were  able  to  excite  rhythmic  muscular 
contraction  but  they  also  added  lithium,  caesium,  and  rubidium 
to  the  list  of  bases,  and  the  salts  of  bromin,  iodin,  and  iron  to 
those  of  carbon,  chlorin,  and  phosphorus.  These  movements 
are  periodic  and  continue  into  the  second  day,  even  at  room 
temperatures. 

Loeb  determined  that  if  a  muscle  be  immersed  in  a  0.7  per  cent 
solution  of  sodium  chlorid,  contractions  will  begin  in  from  sixty 
to  ninety  minutes,  but  that  "  if  a  trace  of  alkali  is  added,  con- 
tractions begin  much  sooner."  This  acceleration  he  attributes 
to  the  hydroxyl  (OH)  in  the  alkali  added.  Not  only  that,  but  r^ 
ascribes  the  effect  to  the  H  involved  in  the  hydroxyl,  because 
the  same  action  follows  the  addition  even  of  inorganic  acids,  as 
HNO3,  "if  the  same  number  of  hydrogen  ions  are  contained 
in  the  unit  volume";3  but  Loeb  hastens  to  assure  us  that 
neither  the  hydrogen  ions  nor  the  hydroxyl  ions  "  belong  to 
those  which  are  capable  of  liberating  rhythmic  contractions." 
They  only  accelerate  the  action  of  those  which  of  themselves 
possess  this  power. 

The  action  of  sodium  and  other  chemicals  in  exciting  contrac- 
tion is,  in  the  opinion  of  Loeb,  to  be  ascribed  to  their  entering 

1  Loeb,  Studies  in  General  Physiology,  Part  II,  p.  518. 
^  Ibid.  pp.  519-538. 
3  Ibid.  p.  527. 


278  CAUSES  OF  VARIATION 

the  muscle  and  there  forming  with  its  substance  definite  com- 
pounds, and  he  believes  the  accelerating  effect  of  H  or  OH  is 
due  to  their  catalytic  action  in  facilitating  the  formation  of  these 
compounds.  In  this  connection  it  is  to  be  remembered  that  the 
serum  of  the  body  which  bathes  the  muscles  is  always,  in  health, 
strongly  saline  and  slightly  alkaline. 

Further  experiments  clearly  showed  that  the  salts  of  potas- 
sium and  those  of  calcium,  magnesium,  strontium,  manganese, 
and  cobalt  tend  strongly  to  prevent  contraction,  this  being  espe- 
cially true  in  the  case  of  potassium  and  calcium,  forcing  the 
conclusion  that  certain  definite  substances  are  necessary  to  con- 
traction ;  that  certain  others  tend  to  accelerate  and  still  others  to 
retard  this  characteristic  activity  of  musctilar  tissue. 

Artificial  parthenogenesis  through  changes  in  the  surrounding 
solution.1  The  indefatigable  labors  of  Jacques  Loeb  upon  this 
subject  have  not  only  thrown  much  light  upon  the  essential 
features  of  fecundation,  but  incidentally  they  have  afforded 
results  of  high  value  in  determining  the  nature  and  range  of 
external  influences  upon  the  characteristic  activities  of  living 
matter.2 

It  had  long  been  known  that  many  of  the  eggs  of  sea 
urchins,  arthropods,  and  marine  worms,  even  when  unfertilized, 
would,  if  left  for  a  comparatively  long  time  in  sea  water,  begin 
to  segment,  reaching  the  two-  and  sometimes  the  four-celled 
stage.  Loeb,  and  later  Morgan,  found  "that  if  the  concentra- 
tion of  the  sea  water  be  raised  sufficiently  by  the  addition  of 
certain  salts,  a  segmentation  of  the  nucleus  takes  place  with- 
out any  segmentation  of  protoplasm  [cytoplasm].  Such  eggs, 
however,  when  brought  back  into  normal  sea  water  divide  into 
as  many  cells  as  there  were  preformed  nuclei."  3  In  none  of 
these  experiments  did  the  cell  division  "  lead  to  the  formation 
of  a  blastula.  A  heap  of  cells,  at  the  best  about  sixty,  were 
formed,  and  then  everything  stopped."  As  in  the  case  of  tumors 

1  Loeb,  Studies  in  General  Physiology,  Part  II,  pp.  539-691. 

2  These  investigations  have  been  published  from  time  to  time,  especially  in  the 
American  Journal  of  Physiology,  and  later  (1905)  in  book  form  under  the  title, 
Studies  in  General  Physiology. 

*  Loeb,  Studies  in  General  Physiology,  Part  II,  pp.  540-541. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION    279 

and  galls,  here  was  growth  without  systematic  differentiation ; 
cell  division  without  the  formation  of  an  embryo. 

Encouraged  by  this  degree  of  segmentation  and  by  his  experi- 
ments upon  irritability  of  muscle,  Loeb  tried  a  great  variety  of 
solutions,  in  various  degrees  of  concentration,  in  the  hope  of 
carrying  the  segmentation  far  enough  to  produce  real  embryos 
and  live,  free-moving  larvae. 

He  was  greatly  hampered  by  the  fact  that  unfertilized  eggs 
do  not  form  membranes  as  do  fertilized,  so  that  growth  tended 
to  be  formless,  and  even  when  assuming  definite  form  in  the 
blastula1  stage  there  were  often  formless  masses  of  dividing 
matter  lying  to  one  side. 

Briefly  stated,  the  following  facts  developed  during  the  prog- 
ress of  this  systematic  experiment : 

1.  In  a  solution  of  sodium  chlorid  the  eggs  were  unable  to 
reach  even  the  blastula  stage. 

2.  With  the  addition  of  MgCl2,  however,  blastulae  were  formed, 
but  they  did  not  move.    When  afterward  placed  in  normal  sea 
water  movement  soon  appeared. 

3.  With  three  chlorids  (Na,  K,  and  Ca)  "the  eggs  not  only 
reached  the  blastula  stage  and  swam  around  in  the  most  lively 
way,  but  they  reached  the  gastrula  and  even  the  pluteus  stage, 
with  the  exception,  however,  that  practically  no  skeleton  was 
formed."  2  Such  larvae  lived  about  ten  days. 

4.  The  addition  of  a  trace  of  Na2CO3  resulted  in  the  formation 
of  a  skeleton,  but  it  was  not  quite  normal.    It  was  made  normal 
by  adding  a  trace  of  MgCl2. 

1  Three  early  stages  are  characteristic  of  the  early  development  of  all  embryos  : 
(i)  the  morula,  or  "mulberry  "  stage,  in  which  cell  division  gives  rise  to  a  globular 
mass  of  rounded  cells,  each  more  or  less  distinct,  like  the  grapes  on  a  bunch  or 
the  seeds  of  a  mulberry ;  (2)  the  blastula  stage,  in  which  the  outer  cells  become 
condensed,  showing  a  distinct  outer  layer,  —  the  blastoderm  ;  and  (3)  the  gastrula 
stage,  in  which  one  side  becomes  pushed  in  (invaginated),  as  one  would  push  in  a 
hollow  rubber  ball  with  his  thumb,  forming  a  kind  of  mouth  and  stomach.    A  few 
forms  never  get  beyond  this  stage,  but  most  pass  quickly  through  it,  differentia- 
tion proceeding  rapidly.    In  higher  animals  the  outer  layer  (ectoderm)  gives  nse 
to  the  skin  and  its  appendages,  the  inner  (endoderm)  to  the   internal  organs. 
Among  sea  urchins,  which  were  here  under  experiment,  the  next  stage  is  known 
as  the  pluteits,  —  the  stage  of  free-moving  larvae.    It  was  this  stage  the  experi- 
menter desired  to  produce. 

2  Loeb,  Studies  in  General  Physiology,  Part  II,  pp.  585~586- 


28o  CAUSES  OF  VARIATION 

5.  All  experiments  indicated  that  it  is  impossible  to  secure 
more  than  the  beginning  of  segmentation  from  an  unfertilized 
egg  without  raising  the  concentration  of  the  sea  water. 

6.  But  for  this  purpose  MgCl2  was  peculiarly  effective  and 
normal  plutei  (free-swimming  larvae)  developed  from  unfertilized 
eggs  lying  in  normal  sea  water  after  having  lain  for  two  hours 
in  a  solution  of  MgCl2  of  proper  strength.1 

7.  These  effects  seemed  to  be  due  to  the  increased  concen- 
tration in  the  sea  water,  bringing  about  increased  osmotic  pres- 
sure and  resulting  in  a  loss  of  water  on  the  part  of  the  egg. 
This  loss  of  water  seems  to  be  the  active  cause  of  rapid  seg- 
mentation, and  a  variety  of  substances  were  discovered  which 
were  able  to  bring  it  about. 

8.  The  principal  difference  noticeable  in  the  plutei  was  that 
those  developed  from  fertilized  eggs  swam  freely  at  the  top  of 
the  water,  while  those  developed  from  unfertilized  eggs  "  were 
all  at  the  bottom  of  the  dish  and  unable  to  rise." 

9.  Experiments  upon  the  marine  annelid  Chaetopterus 2  indi- 
cated that  artificial  development  is   easier  than  with  the  sea 
urchin,  but  that  it  is  achieved  by  a  different  solution.    In  the 
words   of  the  experimenter,  "  We   may  say  that  Chaetopterus 
possesses  a  higher  degree  of  parthenogenetic  tendency  than  the 
Arbacia  [sea  urchin]  eggs,"3  and  "if  the  sea  water  contained 
only  a  slightly  greater  proportion  of  K,  we  should   find  that 
Chaetopterus  was  normally  parthenogenetic."  4 

10.  If  certain  forms  are  prevented  from  becoming  partheno- 
genetic by  the  constitution  of  the  sea  water,  we  may  infer  that 
those  which  are  naturally  parthenogenetic  are  so  by  the  consti- 
tution of  the  blood  or  the  sea  water  enabling  the  egg  to  develop.5 

11.  "The  bridge  between  the   phenomena    of    natural  and 
artificial  parthenogenesis  is  formed  by  those  animals  in  which 

1  Loeb,  Studies  in  General  Physiology,  Part  II,  p.  624. 

2  "  Mead  had  already  found  that  if  0.5  per  cent  KC1  is  added  to  sea  water  the 
unfertilized  eggs  of  Chaetopterus  throw  out  their  polar  bodies,  while  the  addition 
of  0.5  per  cent  NaCl  produced   no  such  effect." — Loeb,  Studies  in   General 
Physiology,  Part  II,  pp.  656-657. 

8  Loeb,  Studies  in  General  Physiology,  Part  II,  pp.  654-655. 
4  Ibid.  p.  665. 
«  Ibid.  p.  683. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION    281 

physical  factors  decide  whether  or  not  their  eggs  develop  par- 
thenogenetically."  1  The  consideration  seems  to  be  largely  one 
of  change  in  osmotic  pressure,  some  organisms  requiring  increase 
and  some  decrease.  Plant  lice  are  parthenogenetic  only  at  high 
temperatures  and  when  the  host  plant  has  plenty  of  water.  "  If 
we  lower  the  temperature  or  let  the  plant  dry  out,  sexual  repro- 
duction occurs."  l  It  seems  to  be  decided  that  Artemia  salina 
living  in  brackish  waters  is  parthenogenetic,  while  its  nearest 
fresh-water  relative,  Branchipus,  is  not.2 

12.  From  the  fact  that  the  beginning  of  segmentation  is  com- 
mon in  unfertilized  and  untreated  eggs  of  many  forms,  it  seems 
to  follow  that  the  effect  of  fertilization  or  of  treatment  is  largely 
to  accelerate  a  process  which  is  able  to  begin  alone  but  which 
proceeds  so  slowly  as  to  be  overtaken  by  destructive  processes 
and  the  death  of  the  egg  before  an  embryo  can  form. 

13.  The  introduction  of  a  small  amount  of  a  catalytic  sub- 
stance at  the  critically  proper  time  (at  maturity)  seems  in  most 
cases  necessary  to  a  cell  division  sufficiently  rapid  to  insure  the 
continuation  of  life. 

14.  The  function  of  the  spermatozoon  would  seem  therefore 
to  be  twofold,  —  first,  to  introduce  such  a  catalytic  substance, 
and  second,  to  convey  hereditary  material. 

No  student  can  consider  these  fundamental  matters  and  fail 
to  realize  the  profound  effect  of  external  influences  upon  in- 
ternal activities,  nor  can  he  avoid  the  conclusion  that  we  must 
revise  our  ideas  as  to  the  relation  even  of  inorganic  chemistry 
and  physical  forces  to  the  processes  of  life.  Much  that  we 
have  considered  as  morphological  and  peculiarly  vital  is,  after 
all,  evidently  due  to  the  operations  of  ordinary  chemical  and 
physical  laws.  This  does  not  make  the  facts  of  variability 
less  significant,  but  it  does  show  the  extent  to  which  living 
organisms  have  become  accustomed  to  their  ordinary  sur- 
roundings. 

1  Loeb,  Studies  in  General  Physiology,  Part  II,  p.  683. 

2  "  Janosik  has  found  segmentation  in  the  unfertilized  eggs  of  mammalians." 
—  Loeb,  Studies  in  General  Physiology,  Part  II,  p.  543.    Loeb  expresses  the  con- 
viction that  possibly  "only  the  ions  of  the  blood  prevent  the  parthenogenetic 
origin  of  embryos  in  mammalians,"  and  that  a  change  in  their  blood  might  be 
followed  by  parthenogenetic  development. 


282  CAUSES  OF  VARIATION 

SECTION   IX  — EFFECT  OF   SALINE  SOLUTION  UPON 
DEVELOPMENT  IN  AQUATIC  ANIMALS 

Sea  water  differs  from  fresh  water  in  two  particulars,  salinity 
and  density,  both  of  which  exert  marked  influence  upon  animal 
life  and  between  which  it  is  often  difficult  to  discriminate.  A 
goldfish  plunged  into  sea  water  at  first  shows  "  violent  incoor- 
dinated  movements,"  but  shortly  "  becomes  immobile  and  rises 
to  the  surface  by  virtue  of  its  lower  specific  gravity."  l 

"  The  effect  of  fresh  water  upon  marine  organisms  is  equally 
striking.  They  go  immediately  to  the  bottom  and  move  with 
difficulty.  Swimming  animals  swim  badly  if  at  all,  and  small 
fishes  have  to  make  much  exertion  to  rise  to  the  surface."  x 

On  many  marine  animals,  as  mollusks  and  fish,  fresh  water 
acts  as  an  anaesthetic,  the  mollusks  soon  yielding  to  paralysis, 
the  fish  appearing  to  suffer  from  lack  of  air.  "  The  respiratory 
movements  become  deep  and  rapid.  ...  The  tissues  become 
swollen  so  that  soft-bodied  animals  are  visibly  deformed, — in 
fishes  the  eyes  are  forced  out,  the  foot  of  gastropods  swells,  the 
blood  corpuscles  swell  up  and  burst,  and  muscular  tissue  may 
increase  as  much  as  six  times  in  volume."  2 

Many  of  these  effects  are  clearly  due  to  differences  in  pres- 
sure which  may  amount  to  many  atmospheres,  but  it  remains 
to  separate,  so  far  as  may  be,  the  effects  of  salinity  from  those 
of  specific  gravity. 

Rather  startling  claims  have  been  made  from  time  to  time 
as  to  the  conversion  of  one  species  into  another  by  altering  the 
degree  of  salinity.  Further  investigation  seems  to  show  that  in 
all  such  cases  intermediate  forms  are  known  to  occur,  which 
argues  that  the  two  forms  which  had  been  recognized  as  dis- 
tinct were  not  both  good  species ;  that  is  to  say,  it  is  a  case  of 
one  species  with  wide  variability  as  to  certain  characters,  not  that 
of  two  distinct  and  well-defined  species.  If,  however,  differences 
in  salinity  are  effective  in  bringing  about  alterations  in  even  a 
single  character,  the  fact  is  of  interest  here,  no  matter  what 
specific  lines  should  be  drawn  by  the  biologist. 

1  C.  B.  Davenport,  Experimental  Morphology,  Part  I,  p.  79. 
-  Ibid.  pp.  79,  80. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION     283 

The  small  crustaceans  Artemia  salina  and  A.  milhausenii 
have  been  recognized  as  distinct,  the  former  living  in  brackish 
and  the  latter  in  still  more  concentrated  waters,  the  two  differ- 
ing mainly  in  the  number  and  length  of  bristles  borne  at  the 
extremity  of  the  caudal  fins. 

Early  in  the  seventies  Schmankewitsch  published  an  account 
of  the  mutual  conversion  of  each  form  into  the  other,  but  the 
facts  as  given  by  him  have  been  greatly  overstated,  as  frequently 
happens  in  repetition.  They  are  sufficiently  significant  as  first 
reported,  and  it  seems  well  to  give  the  original  statement  as 
recorded  by  Bateson,1  which  is  as  follows : 

The  salt  lagoon,  Kuyalnik,  was  divided  by  a  dam  into  an  upper  and  a 
lower  part ;  the  waters  in  the  latter  being  saturated  with  salt,  while  the 
waters  of  the  upper  part  were  less  salt.  By  a  spring  flood  in  the  year  1871 
the  waters  of  the  upper  part  of  the  lake  swept  over  the  dam  and  reduced 
the  density  of  the  lower  waters  to  8°  Baume'  (=  about  sp.  g.  1.051),  and 
in  this  water  great  numbers  of  A.  salina  then  appeared,  presumably  having 
been  washed  in  from  the  upper  part  of  the  lake  or  from  the  neighboring 
salt  pools.  After  this  the  dam  was  made  good  and  the  waters  of  the  lower 
lake,  by  evaporation,  became  more  and  more  concentrated,  being,  in  the 
summer  of  1872,  I4°B  (about  sp.  g.  1.103);  in  l873>  l8°B  (about  sp.  g. 
1.135)  ;  in  August,  1874,  23.5°B  (about  sp.  g.  1.177),  and  later  in  that  year 
the  salt  began  to  crystallize  out.  In  1871  the  Artemia  [as  first  carried 
over]  had  caudal  fins  of  good  size,  bearing  eight  to  twelve,  rarely  fifteen 
bristles,  but  with  the  progressive  concentration  of  the  water  the  genera- 
tions of  Artemia  progressively  degenerated,  until  at  the  end  of  the  summer 
of  1874  a  large  part  of  them  had  no  caudal  fins,  thus  presenting  the 
character  of  A.  milhausenii.  —  FISCHER  AND  MILNE-£DWARDS. 

Bateson  adds  : 

A  similar  series  was  produced  experimentally  by  gradual  concentration 
of  water,  leading  to  the  extreme  form  resembling  A.  milhausenii.  It  was 
found  also  that  if  the  animals  without  caudal  fins  were  kept  in  water  which 
was  gradually  diluted,  after  some  weeks  a  pair  of  conical  prominences, 
each  bearing  a  single  bristle,  appeared  at  the  end  of  the  abdomen. 

The  experimenter  also  relates  that  by  breeding  salina  in  still 
more  diluted  water  he  attained  a  form  resembling  Schaffer's 
genus  Branchipus.  But  the  principal  difference  between  the 
genera  is  that  in  Artemia  the  last  segment  is  about  twice  as 

1  Bateson,  Materials,  etc.,  p.  96. 


284  CAUSES  OF   VARIATION 

long  as  each  of  the  others,  while  in  Branchipus  it  is  divided.  It 
is  extremely  significant  that  this  division  should  be  produced  in 
Artemia  by  culture  in  comparatively  fresh  water,  but  the  fact  is 
no  warrant  for  the  assertion  that  one  genus  can  be  converted 
into  another  by  altering  the  environment.  It  rather  casts  doubt 
upon  the  wisdom  of  a  classification  which  establishes  generic  dis- 
tinctions upon  differences  so  slight  and  so  easily  brought  about. 

The  same  experimenter  studied  species  of  the  genus  Daphnia, 
and  found  "  in  their  case  also  considerable  structural  and  physi- 
ological changes,  the  fresh-  and  salt-water  forms  differing,  in  his 
opinion,  by  characters  usually  held  to  be  specific."  1 

Bateson  studied  the  common  cockle,  a  mollusk,  everywhere 
present  in  the  Aral  Sea  and  its  outlying  waters  of  different 
degrees  of  salinity.  One  of  the  lakes  (Shumish  Kul)  on  its 
western  shore  exhibited  no  less  than  seven  distinct  terraces, 
held  to  represent  successive  stages  of  the  water  levels  during 
its  long  period  of  drying  up,  with  corresponding  increase  in 
salinity.  The  most  noticeable  differences  in  the  shells  taken 
from  these  successive  terraces,  and  presumably  due  to  increas- 
ing salinity,  are  outlined  as  follows  : 2 

1.  A  diminution  in  the  thickness  of  the  shells,  first  apparent 
in  the  third  terrace.    Iri  the  seventh  terrace  this  change  was  so 
marked  that  the  shells  were  almost  horny,  and  their  weight  was 
not  a  third  of  that  of  the  shells  from  the  first  two  terraces. 

2.  Diminution  of  the  size  of  the  beak  [with  the  lowering  of 
the  level]. 

3.  High  coloration.    [The  author  does  not  state  which  way 
the  changes  ran,  whether  up  or  down  the  terraces,  but  he  re- 
marks that  all  the  shells  of  a  given  terrace  were  "  very  nearly 
alike  in  texture,  thickness,  and  degree  of  coloration."  ] 

4.  Grooves  between  the  ribs  appearing  on  the  inside  of  the 
shell  as  ridges  with  rectangular  faces. 

5.  A  great  diminution  in  absolute  size  of  the  shells  on  the 
lowest  terrace. 

6.  Alteration  in   proportion   of  length  to  breadth,  ranging 
from  i  to  0.80  in  the  shells  of  the  first  terrace  to  i  to  0.725  in 
those  of  the  seventh  and  i  to  0.66  on  the  shores  of  neighboring 

1  Vernon,  Variation  in  Animals  and  Plants,  p.  275.          2  Ibid.  pp.  275,  276. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION    285 

lakes.  In  view  of  these  facts  Bateson  remarks,  as  quoted  by 
Vernon,1  "  It  seems  almost  certain  that  these  conditions  are  in 
some  way  the  cause  of  the  variations." 

Biological  literature  is  full  of  similar  examples  of  the  char- 
acteristic effects  of  varying  degrees  of  salinity.  The  limits  of 
space  forbid  the  further  pursuit  of  a  subject  which  might  be 
extended  almost  indefinitely.  It  may  be  sufficient  to  say  that 
the  specific  influence  of  salinity  upon  certain  characters  is, 
beyond  a  doubt,  well  established. 


SECTION  X  — INFLUENCE  OF  USE  AND  DISUSE  UPON 
DEVELOPMENT 

No  fact  is  better  or  more  generally  known  than  that  use  stim- 
ulates and  disuse  dwarfs  the  development  of  many  organs.  To 
say  that  development  is  in  proportion  to  use  would  doubtless 
be  true,  roughly  speaking,  of  certain  parts,  as  the  muscular 
system,  secreting  glands,  etc.  It  certainly  would  not  be  true 
of  many  others,  as  hair,  feathers,  bony  skeleton,  etc.,  which 
develop  independently  of  use,  and  some  of  which,  as  hair  and 
feathers,  involve  no  activity  in  the  sense  in  which  the  term  is 
here  understood. 

This  discussion  should  be  limited  to  the  distinctively  active 
parts,  and  the  influence  of  exercise  or  the  lack  of  exercise  upon 
their  development.  Of  these  parts  it  may  fairly  be  said  that 
perfect  development  is  dependent  upon,  if  not  proportional  to, 
the  degree  of  their  use,  especially  during  the  earlier  stages  of 
development. 

The  classic  illustration  from  Darwin,  showing  the  leg  bones 
of  the  tame  duck  and  the  wing  bones  of  the  wild  duck  to  be 
relatively  heavier ;  the  arm  of  the  artisan  and  the  body  of  the 
athlete  ;  the  training  of  the  track  horse  ;  the  marvelous  coordi- 
nation of  complicated  nervous  impulse  and  muscular  response 
in  the  violinist  and  the  pianist, — all  these  and  a  multitude  of 
similar  facts  teach  clearly  that  individual  development  of 
usable  parts  depends  very  much  upon  their  early  and  continuous 
exercise. 

1  Vernon,  Variation  in  Animals  and  Plants,  p.  277. 


286  CAUSES  OF  VARIATION 

Upper  limits  of  development.  In  what  sense  is  development 
conditioned  upon  use  ?  Does  use  simply  enable  the  part  to 
attain  its  normal  and  proper  development,  to  which  it  is  entitled 
under  the  laws  of  heredity,  or  does  it  stimulate  development 
beyond  the  normal? 

Some  biologists  at  once  assume  the  latter  to  be  impossible 
and  that  any  unusual  appearance  is  a  case  of  atavism.  It  is  true 
that  in  times  long  past  there  may  have  existed  ducks  that  walked 
and  others  that  flew  more  and  better  than  those  which  Darwin 
examined  ;  but  when  did  nature  produce  a  running  or  a  trotting 
horse  as  good  as  the  one  of  to-day  ?  To  what  remote  ancestor 
do  our  violinists  and  our  pianists  owe  their  skill,  and  what  was 
the  instrument  on  which  they  acquired  it  ? 

The  accompanying  cut  is  a  facsimile  of  a  properly  attested  let- 
ter written  with  the  feet  by  a  young  woman  twenty-three  years 
old  who  lost  both  arms  at  the  age  of  ten.  Among  her  other  ac- 
plishments  she  numbers  cutting,  sewing  (threading  her  own 
needle),  drawing,  sweeping,  and  a  great  variety  of  housework.1 

Here  is  a  case  of  putting  parts  to  an  entirely  new  use, 
demanding  a  nicety  of  adjustment  that  was  never  acquired  even 
in  one  out  of  a  million  of  the  ancestors.  Could  there  be  better 
evidence  of  the  fact  that  few  individuals  ever  use,  and  there- 
fore few  ever  develop,  more  than  a  fraction  of  the  capacities  born 
in  them ;  that  the  possibilities  of  life  are  seldom  realized,  and 
that  never  are  all  faculties  developed  to  their  utmost  in  any 
single  individual  ? 

All  this  is  clear  but  it  is  not  so  easy  to  determine  where  to 
draw  a  line  and  say,  "  All  development  below  this  is  due  to 
inheritance  and  all  above  to  use."  The  truth  would  seem  to  be 
that  development  depends  upon  both  inherent  tendencies  and 
external  conditions  affording  opportunities  for  their  exercise, 
and  that  the  maximum  of  development  is  reached  only  when 
both  are  at  their  optimum.  There  is  much  force  in  the  word 
"  optimum."  Too  much  exercise,  too  much  food,  too  much 
temperature,  or  too  much  of  any  of  the  conditions  of  life  is 
as  unfortunate  as  too  little. 

1  The  author  saw  one  man  who  wrote  with  his  feet,  but  they  were  attached 
directly  to  the  body,  with  no  legs  whatever. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION    287 


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FIG.  30  illustrates  the  ability  of  a  highly  developed  part  to  perform  an  extremely 
unusual  service.  The  above  letter  was  written  with  the  feet  instead  of  with 
the  hands 

It  is  as  futile  to  attempt  to  decide  whether  internal  or  exter- 
nal circumstances  are  more  helpful  in  development  as  it  is  to 
attempt  to  say  whether  food  or  heat  is  more  essential  to  life. 
Both  are  absolutely  necessary,  and  it  suffices  present  purposes 
if  the  student  understands  that  external  conditions,  even  to  the 
matter  of  exercise,  are  fundamentally  essential  to  full  develop- 
ment, and  that  the  "limiting  element"  may  be  found  external 
to  the  organism  as  well  as  internal.  We  shall  not  be  able  to 
assert  how  much  is  due  to  each  separately,  nor  can  we  determine 
the  coefficient  to  be  assigned  to  use  and  to  disuse,  but  we  are 
safe  in  resting  assured  that  for  many  parts  development  is  fairly 
proportional  to  exercise,  at  least  within  the  limits  of  inheritance. 


288  CAUSES  OF  VARIATION 

Disappearing  organs.  The  disappearance  of  legs  from  snakes 
and  from  whales,  the  lessening  of  the  fore  arms  of  the  kangaroo, 
and  of  the  wing  of  certain  birds,  the  loss  of  toes  from  many 
mammals,  and  rudimentary  conditions  generally,  argue  for  the 
gradual  disappearance  of  a  part  that  is  no  longer  useful  and  no 
longer  used. 

The  first  stages  of  this  disappearance  can  be  understood  as 
arising  through  the  cessation  of  selection  and  the  resulting  pan- 
mixia,1 by  which  inheritance  is  from  the  general  average  of  the 
whole  race,  instead  of  from  a  selected  lot,  as  heretofore,  result- 
ing necessarily  in  degeneration  as  compared  with  a  standard 
sustained  by  rigid  selection.  Later  stages  may  be  explained  by 
"  reversal  of  selection,"  when  the  hitherto  useful  organ  has  not 
only  become  useless  but  in  some  way  detrimental.  This  would 
account  for  still  further  degeneracy,  and  is  as  far  as  the  princi- 
ple of  use  and  disuse  applies.2 

Space  cannot  be  taken  here  for  the  enumeration  of  instances 
showing  the  effects  of  use  and  disuse.  They  may  be  found  on 
every  hand,  and  they  abound  in  books  on  general  evolution.3 

Hypertrophy.  Unusual  enlargement  of  a  part  is  technically 
known  as  hypertrophy.  Two  kinds  are  recognized,  — functional 
hypertrophy,  when  a  part  is  enlarged  through  use ;  and  com- 
pensating hypertrophy,  which  takes  place  when,  one  organ 
being  removed  or  becoming  functionless,  another  enlarges.4 

The  voluntary  muscles  of  the  hand  and  arm  grow  large 
through  heavy  use,  but  the  muscles  of  the  fingers  of  a  musician 
do  not  undergo  hypertrophy,  though  the  total  amount  of  work 
may  be  very  large.  It  is  only  when  muscular  work  is  done  against 
great  resistance  that  enlargement  of  the  muscles  takes  place.6 

1  A  term  coined  by  Weismann  and  denoting  "  universal  crossing,"  literally 
"  all  mixed."  See  Weismann,  Essay  on  Heredity,  I,  91,  141  ;  also  Romanes,  Dar- 
win and  After  Darwin,  Part  II,  pp.  291-306. 

2  For  fuller  discussion  of  disappearing  organs,  see  next  chapter. 

8  Darwin,  Origin  of  Species  (sixth  edition),  pp.  108-112  [D.  Appleton  & 
Company]  ;  also  Animals  and  Plants  under  Domestication  (second  edition) 
[D.  Appleton  &  Company]  :  in  general,  II,  285-293,  345,  346;  in  rabbits,  I,  129- 
134;  in  ducks,  I,  299-301. 

4  Morgan,  Regeneration,  pp.  115-118. 

6  Of  course  the  effects  of  use  are  not  limited  to  increase  of  size ;  they  are  fully 
as  noticeable  in  nicety  of  adjustment. 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION    289 

When  one  kidney  is  removed  from  either  man,  rabbit,  or 
dog,  the  other  becomes  enlarged  and  the  total  amount  of  urea 
excreted  is  unchanged,  and  this  is  true  even  if  the  removal  is 
made  at  maturity,  after  the  parts  have  reached  their  probable 
full  development. 

This  is  allied  to  the  fact  that  the  full  amount  of  urea  is 
excreted  at  once  upon  the  removal  of  one  kidney,  proving  that 
its  fellow  is  able  to  increase  its  labor  even  before  hypertrophy, 
and  showing  that  under  normal  conditions  the  kidney  is  not  fully 
worked.  There  is  first  an  increased  flow  of  blood,  then  increased 
excretion,  then  increased  size.  The  same  is  true  of  the  salivary 
glands,  the  mammae  of  the  female,  the  testes  of  the  male,  and 
quite  likely  of  paired  organs  generally. 

When  the  spleen  is  removed  the  "  lymphatic  glands  of  other 
parts  of  the  body  become  enlarged."  1  Another  kind  of  compen- 
sating development  is  the  well-known  increase  of  one  faculty 
when  another  is  extinct,  as  the  hearing  and  the  touch  of  the 
blind.  In  this  instance,  as  in  learning  to  write  with  the  feet, 
the  part  is  not  only  developed  and  trained  to  its  utmost,  but 
the  undivided  attention  is  fixed  upon  the  matter  in  hand. 

The  student  who  bestows  careful  study  upon  the  relation  of 
the  individual  to  his  environment  will  arrive  at  three  definite 
conclusions  : 

1.  The  impulse  to  development  and  its  chief  directive  forces 
are  within. 

2.  But  the  possibilities  of  that  development,  in  kind  as  well 
as  in  degree,   lie  very  largely   in  surrounding  conditions  and 
entirely  external  to  the  organism. 

3.  These  surrounding  conditions,  therefore,  while  not  logically 
causes  of  variation,  since  they  cannot  bring  about  a  development 
whose  tendency  does  not  already  exist,  are  yet  the  limiting  ele- 
ments to  all  development,   and  many  of  these  conditions  are 
chemical  and  physical  forces  able  to  exert  strongly   directive 
influences  upon  growth  capable  of  differentiation  in  more  than 
one  direction.    On  this  point  see  also  the  chapter  on  "  Relative 
Stability  and  Instability  of  Living  Matter." 

1  Morgan,  Regeneration,  p.  118. 


290  CAUSES  OF  VARIATION 

SECTION  XI  —  EXTERNAL  INFLUENCES  AS  CAUSES  OF 
VARIATION  IN  TYPE 

The  student  must  distinguish  clearly  between  the  influence 
of  external  conditions  upon  an  occasional  individual  and  their 
effect  upon  the  type  of  the  race.  There  are  three  possible  ways 
in  which  the  environment  may  result  in  a  modification  of  type  : 
(i)  by  affecting  all  individuals  in  the  same  way;  (2)  by  selec- 
tion ;  (3)  by  the  inheritance  of  the  modifications  due  to  condi- 
tions of  life.  It  remains  to  examine  each  somewhat  carefully. 

All  individuals  affected  in  the  same  manner,  thus  influencing 
the  type  directly.  The  modifying  effects  of  the  conditions  of  life 
have  been  quite  fully  noted.  If  but  few  individuals  are  affected, 
it  is  manifest  that  the  type  will  not  be  seriously  changed ;  but 
if,  on  the  other  hand,  every  individual  is  affected,  and  in  the 
same  way,  then  the  type  is  to  that  extent  due  to  the  conditions 
of  life. 

For  example,  size  is  directly  influenced  by  the  food  supply, 
and  increase  of  size  in  a  race,  contemporaneous  with  a  better 
food  supply,  may  fairly  be  attributed  to  the  favorable  influence 
of  full  feed  acting  upon  all  individuals  alike. 

Size  is  also  inherited,  so  that  the  limits  of  development  are 
due  to  two  influences  acting  together,  —  inheritance  and  food 
supply.  It  is  often  exceedingly  difficult  to  determine  how  much 
to  attribute  to  the  one  influence  and  how  much  to  the  other. 

What  is  true  of  size  in  this  respect  is  true  of  every  other  char- 
acter that  is  in  the  slightest  degree  dependent  upon  environment 
for  its  development.  Accordingly  much  uncertainty  prevails  as 
to  the  comparative  influence  of  inheritance  and  environment. 
The  racial  type  can  be  determined  only  by  the  study  of  the  indi- 
viduals constituting  the  mature  population  ;  but  their  develop- 
ment is  the  result  of  two  sets  of  causes,  —  the  one  of  heredity, 
the  other  of  environment,  —  both  contributing  to  the  same  effect 
and  both  continuous  through  life. 

Under  the  old  view  every  individual  was  regarded  as  the  re- 
sult not  only  of  what  was  born  into  it  but  also  of  the  direct 
influence  of  its  environment.  Individuals  constitute  the  type, 
and  so  it  is  that  when  the  conditions  of  life  affect  all  individuals 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION    291 

alike  they  necessarily  influence  the  type  of  the  race,  but  to 
what  extent  cannot  be  told  without  some  method  of  subtracting 
the  normal  results  of  simple  inheritance.  No  method  of  doing 
this  has  ever  been  discovered,  and  much  uncertainty  has  always 
prevailed  as  to  what  proportion  of  existing  types  should  be 
credited  to  the  conditions  of  life. 

The  puzzling  problem  is  greatly  simplified  if  we  enlarge  the 
meaning  of  the  word  "  inheritance  "  to  cover  not  only  the  lines 
of  possible  development  but  the  full  capacity  as  well.  In  this 
view  of  the  case  the  individual  and  the  race  are  understood 
as  possessing  hereditary  capacities  for  development  far  beyond 
that  for  which  opportunities  are  likely  ever  to  be  afforded  by 
environment.  This  largely  removes  the  conditions  of  life  from 
among  the  fundamental  causes  of  variability  and  relegates  them 
to  the  realm  of  passive  and  permissive,  though  necessary,  requi- 
sites for  the  full  display  of  hereditary  power.  It  tends  strongly, 
too,  to  regard  most  individuals  as  something  less  than  would 
be  indicated  by  their  hereditary  possibilities,  and  to  consider 
environment  in  general  as  the  limiting,  not  the  stimulating, 
element  in  development.  With  this  view  the  writer  is  inclined 
to  agree,  though  it  necessarily  reduces  the  extent  of  direct 
influence  of  the  environment.  The  student  is  never  to  forget 
that,  whatever  may  be  the  influence  of  surrounding  conditions 
upon  one  form  of  life,  the  same  influences  affect  other  species 
differently,  thus  showing  that  their  characteristic  effect  is  con- 
ditioned upon  the  power  of  the  organism  to  react,  —  a  condition 
that  is  eminently  internal  and  inheritable. 

Selection  as  a  cause  of  variation  in  type.  Many  individuals 
are  unable  to  meet  the  conditions  of  life  with  which  they  find 
themselves  surrounded,  and  in  the  attempt  become  extinct. 
This  is  selection,  and  it  is  manifest  that  the  prevailing  type  of 
the  race  as  it  exists  at  any  moment,  being  made  up  of  selected 
individuals,  is  something  different  from  that  which  was  born 
into  the  race.  It  is  also  manifest  that  only  a  limited  portion  of 
adults  will  reproduce,  so  that  selection  through  the  external  con- 
ditions of  life  exerts  a  strong  influence  upon  type. 

Selection  is  therefore  one  of  the  most  powerful  —  if  not  the 
most  powerful— influences  known  in  the  modification  of  species, 


292  CAUSES  OF  VARIATION 

and  it  may  be  fairly  spoken  of  as  a  primary  cause  of  variation  in 
type.  This  does  not  make  it,  however,  like  temperature  or  food 
supply,  a  fundamental  cause  of  variation  in  living  matter.  There 
is  no  basis  for  selection  until  differences  have  appeared  from 
other  causes.  When  the  selection  is  made,  based  on  these  differ- 
ences, it  is  certain  to  affect  the  type,  and  it  is  therefore  a  cause 
of  type  variation ;  but  it  was  no  cause  of  the  original  differences 
on  which  its  action  was  predicated,  and  it  is  in  no  sense  an 
original  cause  of  variability.  The  confusion  of  mind  which  causes 
selection  to  be  regarded  as  a  cause  of  variation  has  arisen  from 
a  failure  to  distinguish  clearly  between  the  individual  and  the 
type,  —  between  the  material  on  which  we  can  work  through 
selection  on  the  one  hand,  and  the  finished  product  on  the  other. 

Variation  in  type  through  the  inheritance  of  modifications  due 
to  environment.  Whether  individual  modifications  due  to  environ- 
ment (acquired  characters)  are  inherited  will  be  discussed  in  a 
following  chapter.  It  is  the  purpose  here  only  to  show  the  nature 
of  the  effect  of  such  inheritance  in  case  it  does  occur. 

If  the  modifications  due  to  external  influences  should  per- 
chance be  inherited,  even  in  the  slightest  degree,  then  the  effects 
of  modification  would,  like  those  of  selection,  become  cumulative, 
and  the  type  would  the  more  rapidly  conform  to  the  environment 
and  the  more  rapidly  establish  a  "  fit  "  with  the  conditions  of  life. 

It  is  evident  that  this  is  a  difficult  field.  Merely  through  the 
exigencies  of  maintenance  those  characters  will  develop  best  that 
are  most  favored  by  the  conditions  of  life,  thus  bringing  about 
a  kind  of  mass  response  to  the  exactions  of  the  environment. 
Again,  by  the  principle  of  selection,  only  those  in  fair  accord  with 
the  environment  will  live,  and  this  brings  about  a  still  closer  fit. 
If,  now,  modifications  due  to  environment  were  fully  and  com- 
pletely inherited,  the  adjustment  to  constant  conditions  would 
speedily  become  so  exact  and  complete  as  to  leave  no.  room  for 
selection. 

Few  biologists  are  bold  enough  to  claim  this  extreme  degree 
of  inheritance  of  modifications  due  to  environment.  Many  deny 
it  in  toto.  That  neither  extreme  is  right  is  comparatively  easy 
of  as  good  proof  as  we  are  generally  able  to  bring  in  affairs  bio- 
logical, but  where  between  lies  the  truth  it  is  most  difficult  to 


EXTERNAL  INFLUENCES  AS  CAUSES  OF  VARIATION    293 

determine.  The  first  two  causes  mentioned,  both  of  which  are  cer- 
tainly at  work,  sufficiently  explain  most  phenomena,  but  whether 
there  is  an  additional  fraction  due  to  inheritance,  it  is  most  im- 
portant for  us  to  know. 

It  can  be  but  a  fraction  at  best,  and  being  in  exact  line  with 
selection  and  with  the  direct  action  of  the  conditions  of  life,  it  is 
exceedingly  difficult  of  identification  and  of  separation  from  the 
larger  causes.  If  inheritance  is  to  be  included,  however  minute 
the  fraction  in  a  single  generation,  its  effect  is  cumulative,  and  in 
time  it  would  become  the  most  powerful  and  irresistible  of  all 
causes  influencing  type.  Its  further  consideration  must  be  deferred 
to  a  later  chapter,  but  the  result  of  its  activity,  if  it  has  any,  is 
in  its  influence  upon  type. 

Summary.  Though  the  impulse  to  development  lies  within, 
the  opportunities  for  that  development  and  the  forces  controlling 
subsequent  activities  are  to  be  found  in  the  conditions  of  life 
surrounding  the  organism. 

These  are  generally  insufficient  to  afford  full  development  of 
all  the  possibilities  with  which  the  organism  is  endowed  by  hered- 
ity. Accordingly  the  individual  does  not  express  in  its  own  per- 
sonality the  full  extent  of  its  heritage,  and  individuals  generally 
are  to  be  regarded  as  having  realized  something  less,  rather  than 
something  more,  than  their  birthright. 

Living  matter,  like  non-living  matter,  sustains  definite  relations 
to  external  materials  and  forces,  and  the  chemical  elements  of 
which  it  is  composed  are  not  freed  from  their  ordinary  reactions 
to  other  elements  or  to  chemical  or  physical  energies.  And  so  it 
is  that  living  matter  is  subject  to  both  constructive  and  destructive 
combinations,  and  to  definite  reactions  toward  gravity,  light,  tem- 
perature, electricity,  and  to  chemical  and  physical  forces  generally. 

Herein  lies  the  modifying  effect  of  surrounding  conditions  upon 
the  development  and  activities  of  living  matter.  Endowed  from 
within  with  definite  properties  and  capacities,  their  realization 
depends  very  much  upon  outside  materials  and  forces  which  pro- 
vide the  conditions  under  which  the  definitely  organized  matter 
is  compelled  to  discharge  its  activities,  and  we  do  well  to  become 
somewhat  familiar  with  the  nature  and  extent  of  the  limitations 
thus  imposed. 


294  CAUSES  OF  VARIATION 


ADDITIONAL    REFERENCES 

CERTAIN  HABITS  OF  ANIMALS  TRACED  TO  THE  ARRANGEMENT  OF 
THEIR  HAIR.  By  Walter  Kidd.  Proceedings  of  the  Zoological  Society 
of  London,  II,  145-158. 

EFFECT  OF  CLIMATE  ON  SUGAR  CONTENT  OF  BEETS.  Experiment  Station 
Record,  XIII,  736. 

EFFECT  OF  DARKNESS  UPON  VEGETATION.    Experiment  Station  Record, 

XIII,  651. 

EFFECT    OF    ELECTRICITY    UPON    GROWTH   OF    PLANTS.    Experiment 

Station  Record,  XIV,  346,  352,  548  ;  (Acetylene  Gas  Light),  XIV, 

421,  437;  XVI,  137. 
EFFECT  OF  HUMIDITY  ON  GROWTH.    Experiment  Station  Record,  XII, 

1014. 
EFFECT  OF   PRESENCE   OR   ABSENCE  OF    CERTAIN   SALTS   UPON  THE 

COMPOSITION   OF   THE    CROP.    Experiment   Station   Record,  XIV, 

561-563. 
EFFECT  OF  STARVATION  ON  PLANT  GROWTH  (first,  shortage  of  nitrogen ; 

second,  shortage  of  potassium).    Experiment  Station  Record,  XIV, 

H9.  347- 
EFFECT  OF  WATER  CONTENT  UPON  DEVELOPMENT  OF  WHEAT,  OATS, 

CLOVER,  ETC.    Experiment  Station  Record,  XIII,  125-126,  441-631. 
EXPERIMENTAL  ZOOLOGY.     By  J.   H.   Morgan.     Chapters   II   and   III, 

pp.  1 2-4 1.1 
INJURIOUS  EFFECT  OF  FREEZING  ON  DEVELOPMENT  OF  THE  EMBRYO 

IN  THE  EGG  OF  THE  HEN.    Experiment  Station  Record,  XI,  577. 
VARIATION  OF  ANTHRAX   BACILLUS   WHEN   BRED  UNDER  DIFFERENT 

CONDITIONS.    Experiment  Station  Record,  XIV,  293,  916. 
VARIATION  IN  NITROGEN    CONTENT  OF    WHEAT.    Experiment  Station 

Record,  XIII,  451. 

VARIATION  IN  TUBERCLE  BACILLI  WHEN  FOUND  IN  DIFFERENT  ENVI- 
RONMENT.   Experiment  Station  Record,  XIV,  1121  ;  XV,  188. 
VARIATIONS  CAUSED  BY  FERTILIZATION.    Experiment   Station   Record, 

XIV,  347. 

1  This  excellent  volume  was  not  yet  off  the  press  when  this  copy  was  prepared. 
It  is  especially  recommended. 


CHAPTER  X 

RELATIVE  STABILITY  AND  INSTABILITY  OF  LIVING  MATTER 

In  order  to  guide  the  student  of  breeding  in  forming  his  con- 
ceptions as  to  what  may  and  what  may  not  be  accomplished  in 
the  way  of  modifying  the  form  or  function  of  domesticated  ani- 
mals and  plants,  everything  is  valuable  which  throws  light  upon 
the  degree  of  fixedness  in  living  matter ;  that  is  to  say,  in  the 
relations  that  happen  to  have  become  established  between  the 
essential  characters  of  existing  species. 

When  the  student  for  a  time  bestows  careful  study  upon  varia- 
tion and  comes  to  realize  how  radical  are  some  of  the  departures 
from  type  and  how  sweeping  are  some  of  the  deviations  from  the 
normal,  he  is  led  to  feel  instinctively  that  living  matter  exists  in 
a  state  of  extreme  instability  as  regards  both  form  and  function, 
and  that  almost  anything  is  likely  to  happen. 

When,  however,  he  considers  that,  through  it  all,  distinct  types 
are  preserved  ;  and  when  he  notes  the  singular  persistence  of  cer- 
tain characters  through  all  the  vicissitudes  of  time  and  evolution, 
reappearing  generation  after  generation  when  they  were  supposed 
to  have  been  long  lost,  and  in  many  cases  lingering  after  their 
usefulness  is  past  and  associated  characters  have  been  blotted 
out,  —  when  he  considers  all  this,  the  careful  student  will  realize 
that  stability  and  instability  are  relative  terms,  and  he  will  begin 
seriously  to  inquire  into  the  degree  of  stability  of  the  various  plans 
upon  which  matter  has  been  organized  and  vitalized.  It  is  there- 
fore profitable  to  inquire  somewhat  fully  into  the  relative  stabil- 
ity or  instability  of  those  compounds  that  are  endowed  with  life, 
and  into  their  relative  ability  to  maintain  their  integrity  and  dis- 
charge their  functions  under  conditions  both  normal  and  abnormal. 
The  utility  of  this  inquiry  rests  in  the  light  it  may  throw  upon  the 
extent  to  which  characters  that  have  become  typical  are  fixed  and 
unchangeable,  and  the  extent  to  which  they  may  be  modified. 

295 


296  CAUSES  OF  VARIATION 

SECTION  I  — EVIDENCE  FROM  STABILITY  OF  TYPE 

Although  no  two  individuals  are  alike,  and  although  a  given 
character  differs  greatly  in  different  members  of  the  race,  yet 
there  is  a  specific  type  that  is  always  and  everywhere  present ; 
though  the  elements  are  exceedingly  variable,  yet  the  resultant 
composite  is  remarkably  constant  as  compared  with  other  types. 

In  other  words,  when  we  compare  horses  with  horses  we  are 
impressed  with  the  fact  of  variability,  but  when  we  compare 
horses  with  cattle,  or  even  with  asses,  then  we  are  led  to  marvel 
at  the  fixity  and  persistence  of  type.  In  all  its  variations,  the 
horse  is  still  clearly  a  horse.  Wide  and  profound  as  is  variability, 
it  is  yet  well  .within  limits,  and  certain  types  continue  with 
singular  persistence. 

The  Hubbard  squash  and  the  Morgan  horse  are  good  exam- 
ples of  persistence  of  type.  With  all  the  variability  of  the  Cu- 
curbitaceae,  the  Hubbard  squash  persists,  distinct  in  type  and 
quality.  It  mixes  freely  with  other  types, -but  its  characters  are 
evident  even  then,  and  it  possesses  a  singular  ability  to  free  itself 
from  such  admixtures  and  return  again  to  the  original. 

The  Morgan  horse  is  a  breed  established  by  a  single  animal, 
and  yet,  a  hundred  years  after  the  death  of  Justin  Morgan,  when 
the  per  cent  of  his  blood  is  of  necessity  slight,  the  Morgan 
characters  still  stand  out  clearly,  constituting  a  type  almost  as 
distinct  as  that  of  any  existing  breed.  This  is  the  solitary  known 
instance  of  the  founding  of  a  breed  by  a  single  ancestor.  It 
illustrates  in  a  peculiar  way  the  occasional  extreme  persistence 
of  a  type  once  formed,  and  is  in  marked  contrast  to  the  readiness 
with  which  other  types  break  up  and  disappear. 

The  old-time  persistence  of  the  sloping  rump  in  the  Berkshire, 
of  the  narrow  chest  in  the  Poland-China,  of  lack  of  depth  behind 
in  the  pony-built  Hereford,  of  deficient  crops  in  the  Shorthorn, 
—  these  and  similar  defects  that  might  be  mentioned  illustrate 
the  strength  with  which  certain  characters  continue,  even  in  the 
face  of  the  most  powerful  opposition,  and  argue  strongly  for 
stability  of  type. 

It  is  also  a  general  fact  that  species  hold  their  types  with 
essential  success  under  a  great  variety  of  conditions,  both 


RELATIVE   STABILITY  OF  LIVING  MATTER 


297 


favorable  and  adverse,  yielding  but  slowly,  and  sometimes  not 
at  all,  to  modifying  influences,  and  often  suffering  extinction 
when  a  slight  modification  would  have  resulted  in  preservation. 
Thus  the  oaks  and  the  tulip  tree  have  come  down  to  us  from 
remote  ages  practically  unchanged,  and  the  elephant  is  with  us 
yet,  substantially  the  same  as  he  has  been  for  probably  thou- 
sands of  years. 

And  yet  there  is  constant  variation,  in  these  as  in  more  flexi- 
ble species.  They  have  not  freed  themselves  from  variability, 
even  though  the  species  as  a  whole  has  come  to  be  remarkably 
constant.  Indeed,  the  more  the  question  is  studied,  the  more 
evident  it  becomes  that  a  great  deal  that  passes  for  variability 
is  merely  individual  fluctuation  around  a  practically  stationary 
point,  not  necessarily  involving  actual  change  in  type.  That 
is  to  say,  few  individuals  exactly  reproduce  the  type  of  the 
species,  however  fixed  it  may  have  become ;  most  of  them 
depart  slightly  this  way  or  that,  making  a  great  show  of  varia- 
tion, so  that  we  seem  to  be  in  the  midst  of  bewildering  differ- 
ences, even  though  the  type  is  practically  unchanged.  In  cases 
of  this  sort  deviations  represent  not  so  much  departures  from 
type  as  individual  approximations  to  a  general  average. 

Here  is  ground  very  deceptive  to  the  breeder.  Generally 
speaking,  variation  denotes  flexibility  of  organization,  and  there- 
fore possibility  of  improvement,  but  the  breeder  must  not  assume 
that  great  variation  denotes  large  possibility  for  improvement. 
Fundamentally  it  denotes  quite  as  much  an  inherent  failure  to 
assume  a  distinct  type  ;  and  often  a  lesser  deviation,  repre- 
senting a  true  departure  from  type,  affords  a  far  more  favorable 
basis  for  improvement  than  do  those  deviations  that  after  all 
are  merely  fluctuations  about  a  center  that  has  a  strong  tend- 
ency to  remain  fixed.1 

1  Pearson  believes  that  the  extent  of  variability  cannot  be  reduced  more  than 
about  1 1  per  cent,  however  rigid  the  selection.  He  does  not  claim  that  the  type 
cannot  be  shifted  more  than  that  amount,  but  that,  however  much  it  may  be 
shifted,  there  is  still  variability  about  the  new  center,  and  that  this  variability  is 
at  least  89  per  cent  of  the  original  variability  of  the  race.  See  Pearson,  Grammar 
of  Science,  pp.  481-485  ;  also  chapter  on  "  Selection."  This  subject  will  be  fully 
studied  in  a  succeeding  chapter  entitled  "  Type  and  Variability." 


298 


CAUSES  OF  VARIATION 


SECTION  II— ,  EVIDENCE  FROM  MUTABILITY 
OF  SPECIES 

Species  do  not,  however,  always  remain  unchanged.  On  the 
contrary,  they  frequently  exhibit  a  progressive  development 
truly  marvelous.  Horses,  for  example,  are  traceable  backward 
by  easy  stages  and  well-defined  connecting  links  to  a  time  far 
beyond  the  appearance  of  man  upon  the  earth,  the  line  ending 


Head 


Fore  Foot 


HindFoot 


Teeth 


OneJToe 

Splints  of 

2nd  and  4th 

digits 


OneToe 

Splints  of 

2nd  and  4th 

digits 


Protohippus 


Mesohippus 


ThreeToes 

Side  toes 

not  touching 

the  ground 


ThreeToes 

Side  toes 

not  touching 

the  ground 


Long- 
Crowned, 
Cement- 
covered 


Three  Toes 

Side  toes 

touching  the 

ground} 
Splint  of  Sthdigit 


Protorohippus 


ThreeToes 

Side  toes 

touching  the 

ground 


Four  Toes 


Short  - 
Crowned, 
without 
Cement 


Hyracothermm 
(Eohippus} 


FourToes 
Splint  of 
1st  digit 


ThreeToes 
Splint  of 
5th  digit 


FIG.  31.  Comparative  drawings  of  skulls,  feet,  and  teeth  of  prehistoric  horses, 
showing  evolutionary  development.  Reproduced  by  permission  from 
Origin  and  History  of  the  Horse  by  H.  F.  Osborn 

in  one  of  the  earliest  mammals,  a  little  five-toed  creature  not 
much  larger  than  the  domestic  cat. 

No  less  than  twelve  stages  in  this  evolution  are  well  known, 
and  represented  by  specimens  more  or  less  complete  : l 

1  William  D.  Matthew,  of  the  American  Museum  of  Natural  History,  article 
"  Horse,  the  Evolution  of,"  in  Encyclopaedia  Americana.  This  is  one  of  the  best 
and  one  of  the  newest  accounts  of  the  development  of  the  horse,  and  is  chosen  be- 
cause of  its  accessibility  and  reliability.  The  outline  given,  while  not  marked  by 
quotations,  is  practically  an  abstract  of  the  reference. 


RELATIVE  STABILITY  OF   LIVING  MATTER         299 

1.  Hyracotherium.    Skull    only.    Found    in    London  clay    of 
the   Lower   Eocene    (earliest   mammals).    Specimen  in  British 
Museum. 

2.  Eohippus.    Much  better  known,  coming  from  the  Lower 
Eocene  of  Wyoming  and  New  Mexico.    Teeth  like  the  former ; 
four  toes  on  the  front  foot,  with  a  splint  of  the  fifth ;  three  toes 
behind,   with  a  splint   of  another,   showing  that  considerable 
departure  had  already   taken  place  from  its  evident  five-toed 
ancestry.    Height  of  animal  12  to  16  inches. 

3.  Protorohippus  (Wyoming,   1880).    Four  complete  toes  in 
front  and  three  behind ;  no  splints ;  skeleton  of  the  size  of  a 
small  dog.    Described  by  Cope  as  "  the  four-toed  horse." 

4.  Orohippus.  Only  parts  of  jaws  and  teeth,  but  these  show 
some  advance.    Specimen  at  Yale  University. 

5.  Epihippus  (Upper  Eocene,  New  World).    Only  incomplete 
specimens  found,  but  much  time  has  elapsed  and  considerable 
development  is  noted,  especially  in  the   teeth.    The   toes  are 
still  four  and  three,  but  the  central  toe  is  "  becoming  much  larger 
than  the  side  toes." 

Collateral  branches  of  the  same  period  in  the  Old  World 
(Paleotherium  and  Paloplotherium)  had  three  toes  of  nearly 
equal  size  on  each  foot.  They  were  very  abundant  at  this  time 
but  seem  to  have  become  extinct, — a  fate  that  overtook  most 
of  the  branches  of  this  fertile  and  progressive  stem. 

6.  Mesohippus  (White  River  Formation).  Three  toes  on  each 
foot,  the  middle  much  the  largest,  the  side  toes  bearing  little 
weight.    By  this  time  the  animal  ranges  in  size  from  the  coyote 
to  the  sheep,  and  the  molar  teeth  are  well  developed.    All  parts 
of  the  skeleton  known.    Fifth  toe  represented  by  a  splint. 

7.  Anchitherium  (Lower  Miocene).    Found  both  in  Europe 
and  in  America.    Much  like  its  predecessor,  but  larger,  with 
better-developed   teeth.    May  be  one  of  the  "side  branches" 
rather  than  in  the  direct  line  of  the  modern  horse. 

8.  Hypokippus  and  Parahippus.  A  complete  skeleton  of  Hypo- 
hippus    was    found,    1901,   by    the    Whitney   Expedition    near 
Pawnee  Butte,  Colorado.    In  the  forefoot  small  rudiments  still 
represent  the  first    and  fifth   toes,  but  the  splints  are  gone; 
the  second   and  fourth   digits   still  touch   the  ground,   though 


FIG.  32.    Progressive  evolution  in  the  horse  :  the  lower  figure  is  a  full-sized  model 

of  the  Eohippus  in  comparison  with  the  skull  of  the  modern  horse,  showing 

that  the  skull  of  the  latter  horse  is  larger  than  the  entire  body  of  its  ancestor. 

—  From  specimen  in   American   Museum  of  Natural  History,  New  York. 

Courtesy  of  Director  H.  F.  Osborn 


300 


RELATIVE   STABILITY   OF   LIVING  MATTER 


3OI 


lightly.  The  animal  was  of  the 
regarded  as  being  "off  the  direct 
line  of  descent."  See  Fig.  33. 
The  companion  form,  Parahip- 
pus,  is  regarded  as  nearer  the 
line,  having  better  teeth  and 
smaller  side  toes. 

9  and  10.  Protohippus  and 
Pliohippus  (Middle  and  Upper 
Miocene).  Teeth  much  im- 
proved as  grinders,  —  the  val- 
leys being  filled  with  cement, 
—  all  showing  the  appearance 
of  harder  vegetation.  The  side 
toes  (n  and  iv)  are  still  complete, 
but  do  not  touch  the  ground. 
In  some  species  of  Pliohippus 
they  have  almost  disappeared. 

11.  Hipparion  (Pliocene). 
Much     like     Protohippus,     but 
larger,  with   more  complicated 
teeth.     Found  both  in   Europe 
and  in  America,  but  is  probably 
one  of  the  "side  branches." 

12.  Equus    (Pleistocene   and 
Recent).    The  modern  horse,  in 
which  digits  I  and  v  have  en- 
tirely disappeared  and  n  and  iv 
are     represented     by     splints. 
This  single  remaining  branch  of 
the  horse  family  (including  the 
asses)  has  developed  one  of  the 
most  specialized  of  animals.    It 
has    left    behind    many    unsuc- 
cessful   relatives,    representing 
departures   that    proved   either 
unprofitable  or  unfortunate  and 
coming  thus  to  a  more  or  less 


size  of  a  Shetland  pony,  but  is 


FIG.  33.  Three-toed  ancestor  of  the 
horse,— the  Hypohippus :  a  complete 
skeleton  found  in  the  Middle  Mio- 
cene, Colorado,  showing  the  second 
and  fourth  toes  touching  the  ground 
lightly.  —  From  specimens  in  the 
American  Museum  of  Natural  His- 
tory, New  York.  Courtesy  of  Direc- 
tor H.  F.  Osborn 


302  CAUSES  OF  VARIATION 

abrupt  end.  The  modern  horse,  however,  after  his  long  and 
tortuous  evolution,  seems  destined  for  a  prolonged  and  notable 
existence.  During  the  progressive  changes  in  the  feet  the 
leg  has  been  greatly  lengthened,  the  joints  modified  from  the 
loose  ball  and  socket  to  the  firmer  hinge  joint,  and  the  teeth 
have  become  exceedingly  serviceable.  It  is  a  noticeable  fact 
that  the  power  of  a  species  to  withstand  the  vicissitudes  of  ex- 
treme lapses  of  time  depends  very  largely  upon  the  ability  of 
its  feet,  its  legs,  and  its  teeth  to  undergo  modification.  It  has 
been  said  that  the  elephant  has  succeeded  in  maintaining  him- 
self to  the  present  in  spite  of  his  feet,  and  by  virtue  of  his  excel- 
lent teeth  and  his  remarkable  proboscis. 

It  is  noticeable  that  the  larger  part  of  this  evolutionary  his- 
tory of  the  horse  has  been  worked  out  from  specimens  found  in 
western  America,1  but  no  one  believes  that  the  modern  horse 
is  an  American  animal.  This  evolution  seems  to  have  proceeded 
upon  substantially  parallel  lines  in  the  eastern  and  the  western 
continents,  which  were,  during  its  progress,  united  by  a  broad 
strip  of  land  in  the  region  of  Alaska;  but  something  seems  to 
have  happened  to  the  American  branch,  and  it  is  believed  that 
we  are  indebted  to  the  European  and  Asiatic  branch  for  the  horse 
of  the  present. 

Indeed,  South  America  is  represented  by  a  fossil  form  (Hip- 
pidium)  whose  feet  resembled  Equus,  except  that  they  were 
short  and  stout.  Its  teeth  resembled  those  of  Pliohippus  (Museo 
Nacional,  Buenos  Ayres).  This  form  had  evidently  advanced 
nearly  to  that  of  the  present,  but  perished  in  the  general  disaster, 
whatever  it  was,  that  overtook  the  American  horse,  for  it  left 
no  descendants  that  persisted  until  historic  times. 

Causes  of  the  evolution  of  the  horse.  As  is  remarked  by 
Matthew,  "  the  evolution  of  the  horse,  adapting  it  to  live  on  the 
dry  plains,  probably  went  hand  in  hand  with  the  evolution  of 
the  plains  themselves."  At  the  commencement  of  mammalian 

1  Our  knowledge  of  the  evolution  of  the  horse  is  largely  due  to  the  indefat- 
igable labors  of  Professor  Henry  F.  Osborn,  Director  of  the  American  Museum 
of  Natural  History,  and  to  the  magnificent  generosity  of  the  late  William  C. 
Whitney,  through  which  extensive  explorations  and  significant  discoveries  were 
made  in  Wyoming  and  other  regions  of  western  America.  The  student  of  this 
subject  will  eagerly  await  Professor  Osborn's  forthcoming  full  report. 


3°4 


CAUSES  OF  VARIATION 


life  the  Mississippi  valley  was  just  emerging  from  the  Gulf  of 
Mexico,  and  the  plains  of  western  Europe  and  Asia  were  low 
and  wet.  The  climate  was  moist  and  tropical,  stimulating  dense 
and  luxuriant  growth  of  giant  vegetation  even  as  far  north  as 
Greenland.  With  the  Tertiary  came  a  general  elevation,  usher- 
ing in  a  comparatively  cold,  dry  climate,  favorable  to  grasses 
and  the  harder  vegetation  generally.  With  this  came  grassy 
plains  and  the  evolution  of  races  with  good  teeth  and  excellent 
feet  and  legs,  fitting  them  to  a  life  in  the  open. 

With  these  profound  changes  in  nature  other  forms  under- 
went a  development  similar  to  that  of  the  ancestors  and  other 
relatives  of  the  horse.  Many  of  these,  as  our  cattle,  sheep,  swine, 
etc.,  developed  a  two-toed  foot,  and  some,  as  the  rhinoceros, 
stopped  at  the  three-toed  stage,  but  none  of  them  became  so 
highly  specialized  as  the  horse. 

Here  was  a  great  line  of  descent,  continuing  almost  for  ages, 
and  terminating  in  many  highly  specialized  species  that  are  still 
flexible.  But  it  gave  rise  on  the  way  down  (or  up)  to  many  known, 
and  doubtless  to  many  unknown,  branches  that  became  extinct 
through  some  general  disaster,  or,  more  likely,  because  of  their 
inherent  inability  to  develop  all  the  characteristics  necessary  to 
meet  changing  conditions.  For  example,  as  the  teeth  developed 
into  molars  fitted  for  grinding  the  ever-hardening  forage,  some 
species  secreted  cement  in  the  valleys  thus  supporting  the  hard 
and  grinding  ridges;  others  did  not,  and  it  is  significant  that  in 
the  latter  case  no  species  endured.1  The  elephant  alone,  of  his 
kind,  has  persisted  to  the  present,  and  if  this  is  because  of  his 
teeth,  and  in  spite  of  body  and  feet,  which  are  ill  adapted  to 
modern  conditions,  it  serves  to  show  on  how  slender  a  thread 
the  life  of  a  species  often  hangs. 

Present  existing  land  species  are  to  be  regarded  as  representing 
lines  of  descent  naturally  endowed  with  an  unusually  high  degree 
of  flexibility  ;  all  the  more  stable  and  less  adaptable  forms  having 
perished  off  the  earth  in  the  long  struggle  to  keep  up  with  the 

1  It  is  worthy  of  remark  that  the  central  plains  of  South  America  seem  to 
have  developed  a  horse-like  animal  (Litopterna),  losing  its  lateral  toes  and  develop- 
ing the  hinge  joint  and  lengthened  limb ;  but  it  never  developed  cement  in  its 
grinders,  which  remained  inferior,  and  we  are  not  surprised  that  its  line  became 
extinct. 


RELATIVE   STABILITY  OF  LIVING  MATTER        305 

evolution  of  the  world  as  a  whole.  Existing  species  therefore 
represent  the  choicest  material  of  the  organic  world.  Having 
arrived  at  a  high  state  of  differentiation,  they  have  doubtless 
lost  something  of  the  flexibility  that  marked  their  early  and  more 
generalized  forms,  yet  they  are  to  be  regarded  as  "  highly  selected 
material,"  ready  to  the  breeder's  hand  for  still  greater  adapta- 
tion, not  only  to  their  own  needs  but  to  those  of  man. 

Even  when  dealing  with  specially  flexible  forms,  the  breeder 
is  never  to  forget  that  they  are  constantly  giving  rise  to  branches 
that  are  incapable  of  adaptation.  Unhappy  is  the  breeder  who 
devotes  his  life  to  a  branch  of  this  kind,  whether  it  be  among 
horses,  cattle,  or  any  of  the  more  slowly  multiplying  forms,  animal 
or  plant ;  for  no  amount  of  apparent  variability  will  make  up  for 
inherent  defects,  nor  will  it,  seemingly,  avert  the  evil  day  of 
extinction. 


SECTION  III  — EVIDENCE  FROM  REVERSION  AND 
ATAVISM  i 

The  sudden  reappearance  of  a  long-lost  character  serves  to 
remind  us  that  combinations  once  effected  tend  strongly  to 
return.  The  English  breeds  of  cattle  are  supposed  to  have 
descended  from  the  ancient  wild  white  cattle  that  roamed  freely 
over  the  island  until  the  year  1 200  or  later,  when  private  owner- 
ship interfered.  With  the  inclosing  of  the  larger  estates  as  hunt- 
ing parks,  herds  of  these  cattle  were  included  with  other  game 
animals,  and  for  over  six  hundred  years  they  have  lingered  in  this 
semi-wild  condition  at  Chillingham,  Chartley,  and  other  parks. 

1  It  is  important  that  the  student  observe  the  modern  distinction  between 
"  reversion  "  and  "  atavism."  They  both  refer  to  the  reappearance  of  characters 
once  typical  but  now  extinct.  "  Reversion  "  is  the  term  to  use  when  the  character 
belonged  to  a  near-by  ancestor  clearly  of  the  same  species  but  several  generations 
removed,  while  "  atavism  "  is  used  to  denote  the  appearance  of  characters  belonging 
to  exceedingly  remote  ancestors,  perhaps  even  of  different  species.  An  example 
of  reversion  is  the  occasional  appearance  of  the  white  color  in  the  red  breeds  of 
English  cattle,  and  a  good  example  of  atavism  is  the  occasional  persistence  of 
gill  slits  in  mammals,  which  generally  disappear  during  embryological  development 
but  occasionally  remain  as  permanent  openings.  Canine  teeth  in  man,  normally 
present,  are  regarded  as  a  heritage  from  some  primitive  ancestor.  They  may  some 
day  become  atavistic.  The  term  "  reversion  "  covers  most  of  the  breeder's  needs. 
It  is  the  biologist  who  deals  with  remote  species. 


3o6  CAUSES  OF  VARIATION 

During  this  time  there  has  been  (supposedly)  no  admixture 
with  domesticated  herds,  and  yet  there  appears  occasionally, 
even  in  a  Devon  herd,  a  white  calf  whose  ears,  lower  legs,  and 
brush  of  tail  are  marked  with  the  tawny  red  or  brown  of  the 
wild  ancestor,  and  whose  matted,  curly  hair,  upstanding  horns, 
and  peculiar  facial  expression  bespeak  his  reversion  to  the 
early  type. 

This  singular  persistence  of  characters  once  typical  argues 
strongly  for  stability  if  considered  from  the  standpoint  of  the 
ancient  character,  but  it  speaks  not  less  plainly  for  instability  if 
considered  from  the  standpoint  of  the  new  (present)  type. 

The  vermiform  appendix,  the  persistence  of  the  tail  in  most 
mammals,  —  these  and  scores  of  similar  instances  attest  the 
stubborn  resistance  of  a  structural  part  to  the  extinction  that  is 
inevitable ;  and  the  case  of  the  "  beard  "  of  the  turkey  cock 
illustrates  the  fact  that  a  combination  of  whatever  order,  once 
started,  tends  strongly  to  continue,  even  though  useless  and 
unmeaning. 

SECTION   IV  — EVIDENCE   FROM   DISAPPEARANCE 
OF  PARTS 

The  organic  world  is  full  of  instances  of  structural  parts 
lingering  long  after  their  usefulness  has  largely  or  quite  disap- 
peared, and  after  entirely  new  relations  have  been  established 
among  associated  characters.1 

The  hind  legs  of  the  python  and  the  whale,  already  rudimen- 
tary and  represented  only  by  bones  internal  to  the  surface,  and 
those  of  the  sea  lion  and  the  seal,  evidently  disappearing  in  the 
same  manner;  the  wing  of  the  apteryx,  reduced  to  the  merest 
trace  hidden  in  the  plumage,  and  that  of  the  ostrich,  plainly  fol- 
lowing along  to  the  same  fate ;  the  fetal  hair  of  the  whale,  and 

1  This  is  entirely  independent  of  the  question  of  the  influence  of  utility  in  the 
origin  and  development  of  a  new  character.  It  has  been  the  fashion  to  assume 
that  none  but  useful  characters  will  originate.  The  writer,  on  the  contrary,  inclines 
to  the  belief  that  any  character  will  arise  whose  elements  are  present  in  the  organ- 
ism, quite  irrespective  of  its  usefulness,  and  that  it  will  continue  unless  prevented 
by  selection,  although  manifestly  it  will  never  attain  maximum  prominence  except 
through  the  cumulative  effect  of  the  selective  process. 


RELATIVE  STABILITY  OF  LIVING  MATTER 


307 


its  functionless  teeth  reduced  to  the  primitive  conical  form,  yet 
often  accompanied  by  rudimentary  successionals  1 ;  the  splint 
bones  of  horses,  silent  witnesses  of  what  has  befallen  their  neigh- 
bor digits,  and  stern  prophets  of  their  own  extinction  ;  the  rudi- 
mentary muscles  of  the  scalp  and  the  ears  in  man,  —  these  and 
numberless  similar  vestiges  of  the  past  remind  the  student  of  the 
tenacity  with  which  vital  activities  persist  when  once  established, 
producing  a  rudimentary  leg  or  wing,  or  lesser  part,  for  indefi- 
nite generations  after  its  usefulness  has  ceased  and  all  selection 
has  disappeared. 


SECTION  V  — EVIDENCE   FROM   THE   DIRECT  ACTION 
OF  THE  ENVIRONMENT 

All  the  evidence  goes  to  show  that  the  conditions  of  life  exert 
a  direct  and  powerful  action  upon  the  extent  of  development 
and  the  nature  of  the  functions  of  living  matter.  We  have  only 
to  recall  the  characteristic  reactions  of  certain  chemical  sub- 
stances upon  protoplasm,  the  influence  of  light,  gravity,  and 
temperature,  and  the  effect  of  even  so  slight  a  circumstance  as 
contact,  to  realize  that  living  matter  is  exceedingly  dependent 
upon  its  environment.  If  we  should  forget  for  the  moment  that 
racial  lines  are  preserved  distinct  in  spite  of  the  environment, 
we  might  readily  come  to  believe  with  the  Lamarckians  that  the 
conditions  of  life  are  the  supreme  factors  in  directing  evolution 
and  in  fixing  the  type. 

To  enter  fully  into  the  discussion  of  this  phase  of  the  question 
at  this  point  would  be  to  repeat  what  has  been  said  as  to  exter- 
nal causes  of  variation,  or  to  extend  the  examples  cited,  and 
space  can  be  afforded  for  neither.  The  student's  attention  is 
invited  to  this  phase  of  the  question,  however,  for  he  should 
acquire  a  just  and  reasonable  conception  of  the  relative  stability 
of  living  matter  as  shown  by  the  abundance  of  the  class  of  evi- 
dence here  hinted  at  rather  than  fully  exploited. 

1  The  fact  that  successional  teeth  are  formed  in  a  rudimentary  state  argues  for 
the  fact  that  the  teeth  present  are  the  first  or  milk  teeth,  which,  being  functionless, 
are  not  discharged  and  replaced  as  in  mammals  generally,  but,  on  the  contrary, 
persist  through  life. 


308  CAUSES  OF  VARIATION 

SECTION  VI  — EVIDENCE   FROM   ACCLIMATIZATION 

Considerable  light  is  thrown  upon  the  relative  stability  of 
living  matter  and  the  extent  to  which  it  responds  to  external 
influences  by  the  phenomena  of  acclimatization  and  the  kindred 
phenomena  of  immunity. 

Acclimatization  to  chemicals,  especially  poisons.1  "  It  is  clear 
that  the  protoplasm  of  different  organisms  is  dissimilar.  We 
see  this  in  the  different  reactions  to  the  same  chemical  agent. 
Not  only  is  the  reaction  of  the  various  species  unlike,  but  in- 
dividuals of  the  same  species  from  different  localities  differ 
widely."2 

The  common  poison  ivy  produces  extreme  irritation  with  most 
persons,  —  the  effect  being  recurrent  for  many  years,  —  while 
with  others  it  is  entirely  innocuous.  To  even  the  most  viru- 
lent infectious  diseases  many  individuals  are  entirely  immune, 
and  with  nearly  all  diseases  of  this  class  a  single  attack  results 
in  immunity  for  life,  through  some  kind  of  acclimatization.  In 
much  the  same  manner  individuals  become  accustomed  to  the 
sting  of  bees,  and  experience  little  inconvenience  from  what 
would  have  caused  intense  suffering  to  most  others,  or  to  them- 
selves before  acclimatization.  Physicians  find  it  necessary  to 
change  their  remedies  frequently  because  they  soon  lose  their 
characteristic  effect  upon  the  patient. 

In  lower  organisms  the  same  phenomenon  is  noticeable.  Thus, 
"  few  bacteria  can  resist  i  per  cent  of  Na2CO3,  and  even  the 
extremely  resistant  Ascaris  lives  only  [from]  five  to  six  hours  in  a 
5.8  per  cent  solution  of  this  salt";  but  "Loew  has  found  in 
Owen's  Lake,  California  (an  alkaline  water  containing,  among 
other  things,  2.5  per  cent  Na2CO3),  numerous  living  Infusoria, 
Copepoda,  larvae  of  Ephydra,  and  molds."  3 

A  solution  of  acetic  acid  0.23  per  cent  strong  kills'  the  tenta- 
cles of  Drosera,  but  the  vinegar  eel  lives  in  a  4  per  cent  solution. 
Most  protoplasm  is  extremely  sensitive  to  acids  generally,  espe- 
cially to  HC1  and  H2SO4;  but  the  gastric  juice  is  largely  HC1, 
and  "  the  gland  cells  of  some  marine  Gasteropoda  secrete  H2SO4 

1  C.  B.  Davenport,  Experimental  Morphology,  Part  I,  pp.  27-32. 

2  Ibid.  p.  27.  3  Ibid>  p.  28. 


RELATIVE   STABILITY   OF    LIVING   MATTER         309 

of  a  strength  (2  per  cent  to  3  per  cent)  which  is  fatal  to  most 
protoplasm."  1    Davenport  adds  : 

One  general  law  of  high  resistance  is  worthy  of  notice  :  an  organism  which 
produces  an  albuminoid  poison  is  strongly  resistant  to  that  poison.  Thus 
Fayrer  has  shown  that  venomous  serpents  are  not  destroyed  by  the  secretion 
of  their  poison  glands  when  it  is  injected  into  them ;  and  Bourne  has  shown 
that  scorpions  are  not  injured  by  their  own  venom.1 

It  is  a  well-known  fact  that  immunity  from  a  poison  is  gained 
by  frequently  repeated  and  gradually  increased  doses,  beginning 
with  a  minimum  quantity.  Thus  users  of  tobacco,  alcohol,  opium, 
chloral,  etc.,  are  able  to  withstand,  indeed  require  for  comfort, 
amounts  that  would  be  exceedingly  injurious,  even  fatal,  to  one 
not  acclimated  to  its  use.  It  is  said  that  arsenic  eaters  may 
take  with  impunity  as  much  as  0.4  grams,  or  four  times  the 
lethal  dose.1  The  same  results  are  obtained  experimentally. 
Sewall  inoculated  pigeons  with  rattlesnake  poison.  He  found 
that  while  no  unacclimated  birds  could  withstand  one  drop  of  a 
6.8  per  cent  solution  of  venom  in  glycerin,  yet  by  commencing 
with  a  weak  solution  they  were  enabled  to  resist  four  drops  of 
the  fatal  solution.  Kanthack  in  the  same  way  acclimated  two 
rabbits  and  a  hen  to  serpent's  venom.2 

This  method  is  entirely  similar  to  the  one  employed  to  render 
man  immune  to  smallpox,  hydrophobia,  anthrax,  diphtheria,  and 
other  dangerously  infectious  diseases.  The  virus  is  cultivated 
successively  in  the  body  of  a  lower  animal,  until  its  virulence  is 
much  reduced.  Then,  beginning  with  an  exceedingly  attenuated 
solution,  the  patient  is  inoculated  repeatedly  with  virus  of  increas- 
ing strength  until  complete  immunity  is  secured,  or  until  the 
full  strength  may  be  endured  without  serious  consequences. 

Ehrlich  experimented  with  white  mice  in  an  endeavor  to  dis- 
cover the  upper  limits  of  artificial  immunity.  Commencing  with 
a  0.0005  Per  cent  solution  of  ricin,  which  was  the  strongest 
they  could  endure  and  live,  the  strength  was  gradually  in- 
creased to  0.2  per  cent  in  twenty,one  days,  or  to  four  hundred 
times  the  natural  lethal  strength.  Thus  it  may  be  said  that 
these  mice  had  acquired  in  the  period  of  twenty-one  days  an 

1  C.  B.  Davenport,  Experimental  Morphology,  Part  I,  p.  28.  2  Ibid.  p.  29. 


310  CAUSES  OF  VARIATION 

immunity  that  might  be  expressed  as  400  when  compared  with 
the  normal  as  I.  The  increase  was  slow  at  first,  but  had  reached 
twenty  times  the  normal  within  eight  days,  after  which  it  rose 
rapidly.1 

Still  more  significant  are  the  facts  connected  with  the  prepa- 
ration of  diphtheria  antitoxin  from  the  horse.  In  this  process 
Roux  first  mixes  the  filtrate  of  the  bacillus  with  iodin  to  reduce 
its  virulency.  Only  one  quarter  of  a  cubic  centimeter  of  this 
"  iodized  toxin"  is  used  for  the  first  injection,  but  on  the  thir- 
teenth day  a  full  cubic  centimeter  is  used.  uOn  the  seventeenth 
day  one  fourth  cubic  centimeter  of  the  pure  toxin  is  injected, 
and  this  is  gradually  increased  in  amount  till  on  the  forty-first 
day  10  cc.  is  injected  and  on  the  eightieth  day  no  less  than 
250  cc.  The  virulency  of  the  last  dose  must  have  been  some 
five  thousand  to  ten  thousand  times  greater  than  that  of  the  first 
dose,"  showing  the  extent  to  which  the  constitution  of  the  horse 
had  become  acclimated  to  the  poison.2 

Davenport  and  Neal  reared  two  lots  of  stentors,  — one  in  pure 
water,  the  other  in  a  solution  of  0.00005  Per  cent  HgCl2.  After 
two  days  both  lots  were  put  into  a  killing  solution  (o.ooi  per  cent 
HgCl2).  The  resistance  period  of  the  lot  reared  in  plain  water  was 
on  the  average  but  83  seconds,  while  that  of  the  lot  grown  in  the 
weak  solution  was  304  seconds.  Other  experiments  gave  like 
results,  and  from  these  investigations  the  principle  was  deduced 
that  the  resistance  period  varies  directly  with  the  strength  of  the 
solution  in  which  the  protoplasm  has  been  ciiltivated?  As  would 
be  expected,  if  the  culture  solution  should  chance  to  be  only  just 
outside  the  lethal  point,  it  might  permanently  weaken  without 
destroying  life,  in  which  case  successful  acclimatization  would 
not  follow ;  the  animal  would  succumb  through  weakness,  and 
the  principle  stated  would  not  hold  good. 

In  these  experiments  no  deaths  occurred,4  hence  the  results 
must  be  attributed  entirely  to  alteration  of  the  protoplasm  and  not 
at  all  to  selection.  All  these  considerations  point  conclusively 

1  C.  B.  Davenport,  Experimental  Morphology,  Part  I,  p.  29. 

2  Quoted  from  Vernon  (Variation  in  Animals  and  Plants,  p.  387),  who  quotes 
from  Crookshank's  Text-Book  of  Bacteriology,  1896,  p.  58. 

8  C.  B.  Davenport,  Experimental  Morphology,  Part  I,  p.  30. 
4  Ibid.  p.  31. 


RELATIVE  STABILITY  OF  LIVING  MATTER        311 

to  the  fact  that  even  so  stable  and  peculiar  a  compound  as  living 
protoplasm  may  undergo  prof ound  alteration  from  causes  entirely 
external  to  itself. 

Moreover,  this  alteration  is  not  merely  temporary,  but  is 
often  lasting,  even  permanent.  In  the  case  of  Ehrlich's  mice, 
already  referred  to,  individuals  which  had  acquired  an  immunity 
represented  by  200,  and  were  then  kept  on  normal  food  for  6.5 
months,  were  still  found  resistant,  certainly  to  the  extent  of  $O 
(how  much  more  was  not  determined  1).  This  is  in  accord  with 
the  experience  of  arsenic  and  opium  eaters  and  of  alcohol  and 
tobacco  users  :  the  condition  is  more  or  less  permanent,  and  the 
body  craves  the  specific  drug,  which  is  no  longer  poisonous. 

It  agrees,  too,  with  the  experience  in  immunity  from  disease, 
which  is  frequently  permanent  through  life  after  one  attack. 
All  experiments  and  experience  agree  that  immunity  from  one 
poison,  whether  natural  or  acquired,  is  no  guaranty  of  immunity 
in  any  degree  from  another. 

Acclimatization  to  high  temperatures.  All  experiments  indi- 
cate that  death  from  extreme  temperatures  is  due  to  coagula- 
tion of  the  proteids  of  the  protoplasm,  and  that  ordinarily  the 
coagulation  point  is  not  far  above  the  highest  natural  terrestrial 
temperatures,  so  that  most  protoplasms  are  unable  to  resist 
temperatures  above  about  45° C.,  having  apparently  become 
nicely  adjusted  to  natural  conditions  as  generally  encountered. 
Yet  organisms  are  found  in  the  so-called  boiling  springs  at 
temperatures  of  50°,  60°,  85°,  and  even  98°,  which  is  near  that 
of  boiling  water.2  Morgan  mentions  specifically  Leptothrix,  in 
the  Karlsbad  springs,  at  44°  to  54° ;  nostocs  and  Protococcus 
forms  in  the  geysers  of  California  at  93°;  Oscillaria  in  the 
Yellowstone  Park  springs  at  54°  to  68°,  in  the  Philippines  at 
71°,  in  Ischia  at  85°,  and  in  Iceland  at  98°.  He  remarks  that 
these  temperatures  may  be  somewhat  too  high,  because  hot 
springs  are  colder  at  the  edges  than  at  the  center ;  yet  the  heat 
is  extreme,  and  far  above  the  natural  resistance  of  any  known 
form  of  protoplasm.2 

1  C.  B.  Davenport,  Experimental  Morphology,  Part  I,  p.  32. 

2  Morgan,  Evolution  and  Adaptation,  p.  320;  C.  B.  Davenport,  Experimental 
Morphology,  Part  I,  p.  252  (tables). 


312  CAUSES  OF  VARIATION 

The  same  author  mentions  snails  living  in  France  at  35°  to 
36°C.,  and  in  Padua  at  50°;  rotifers  at  Karlsbad  at  45°  to  54°; 
frogs  at  "  Pise  "  at  38°,  and  the  crustacean  Cypris  balnearia  at 
Hammam-Meckoutin  at  81°. 

All  these  are  living  at  temperatures  much  above  the  death 
point  of  their  nearest  relatives,  and  we  are  forced  to  the  conclu- 
sion that  they  have  descended  from  ancestors  living  in  tempera- 
tures not  above  40°  and  not  at  all  able  to  endure  the  extreme 
temperatures  in  which  the  present  generations  live  and  thrive. 
Acclimatization  there  must  have  been,  in  some  way  and  at  some 
time,  and  that  of  extreme  degree,  involving  profound  changes  in* 
the  protoplasm. 

Experiments  throw  interesting  light  upon  the  manner  of  accli- 
matization. "  Dutrochet  found  that  if  the  plant  Nitella  was 
put  into  water  at  27°,  the  currents  in  the  protoplasm  were 
stopped,  but  soon  began  again.  If  put  now  into  water  at  34°, 
they  again  stopped  moving,  but  in  a  quarter  of  an  hour  began 
once  more.  If  then  put  into  water  at  40°,  the  currents  slowed 
down,  but  began  again  later."  * 

Davenport  and  Castle  reared  two  lots  of  tadpoles  from  the 
same  lot  of  recently  laid  eggs.  One  lot  was  kept  at  24°  to 
25°C.,  the  other  at  15°.  "  Both  lots  developed  normally,  the 
former  much  more  rapidly."  At  the  end  of  four  weeks  both 
lots  were  tested  for  heat  rigor  by  gradually  heating  the  water 
in  which  they  were  contained.  Those  reared  at  15°  became 
motionless  at  41°  or  below ;  while  of  those  reared  at  24°  to  25° 
(10°  higher),  no  tadpole  died  under  43°,  the  average  increased 
resistance  being  3-2°.2  The  experimenters  remark  that  this  in- 
creased resistance  was  due  in  no  sense  to  selection,  for  no 
deaths  occurred  during  the  period  of  acclimatization.  It  must 
have  been  due  to  changes  wrought  in  the  protoplasm.  This  con- 
dition was  more  or  less  lasting,  for  the  difference  in  -resisting 
power,  though  lessened,  was  still  noted  after  seventeen  days' 
sojourn  in  cooler  water.3 

1  Morgan,  Evolution  and  Adaptation,  p.  320 ;   C.  B.  Davenport,  Experimental 
Morphology,  Part  I,  p.  252  (tables). 

2  C.  B.  Davenport,  Experimental  Morphology,  Part  I,  p.  253. 

3  Ibid.  p.  254. 


RELATIVE  STABILITY  OF   LIVING  MATTER 


313 


All  experiments  indicate  that  acclimatization  to  extreme  tem- 
peratures is  accompanied  by  a  rise  of  the  optimum.  Thus  Men- 
delssohn placed  Paramecia  in  a  trough  whose  temperature  was 
24°-28°  at  one  end  and  36°-38°  at  the  other.  They  all  col- 
lected at  the  cooler  end.  The  whole  trough  was  then  heated  to 
36°-38°  for  from  four  to  six  hours.  When  the  temperatures  were 
again  brought  to  24°-28°  at  one  end  and  36°-38°  at  the  other, 
they  all  collected  at  the  warmer  end.1  This  experiment  is  akin 
to  that  of  placing  one  hand  in  cold  water  and  the  other  in  hot 
for  a  few  seconds,  and  afterwards  plunging  them  both  into  the 
same  dish.  Whatever  the  temperature  of  this  water,  it  will 
seem  warm  to  one  hand  and  cold  to  the  other.  It  is  supposed 
that  increased  resistance  to  heat  is  accompanied  by  loss  of 
water  in  the  protoplasm. 

Acclimatization  to  cold.  It  is  matter  of  common  experience 
that  both  man  and  the  domestic  animals  become  accustomed  to 
the  cold  of  winter  as  they  do  to  the  heat  of  summer,  and  endure 
without  distress  temperatures  that,  if  suddenly  imposed,  would 
prove  most  uncomfortable.  Certain  species  have  become  so 
attuned  to  cold  as  to  live  and  multiply  in  extremely  low  temper- 
atures. Such  are  the  several  species  of  Protista  that  give  rise 
to  the  "  red  snow"  of  the  arctics,  the  "  glacier  flea"  (Desoria 
glacialis)  living  on  the  Swiss  glaciers,  and  other  species  that 
thrive  where  the  temperature  is  below  the  freezing  point  of 
water.  Swarmspores  are  exceedingly  sensitive  to  cold,  yet 
"  Strasburger  cites  a  case  of  a  marine  alga  in  which  they  were 
being  formed  and  thrown  out  when  the  temperature  of  the  water 
was  between  —1.5°  and  — 1.8°  C."  2 

All  this  shows  that  the  temperatures  at  which  protoplasm  is 
active  are  in  large  measure  dependent  on  the  temperatures  at 
which  the  organism  is  forced  to  live. 

Acclimatization  to  light.  There  are  some  indications  of  a 
constitutional  "  attunement  "  to  light,  which  may  be  altered  by 
exposure  to  changed  intensity,  but  the  matter  is  not  well  worked 
out,  and  more  data  are  required  before  definite  conclusions  can 
be  drawn. 

1  C.  B.  Davenport,  Experimental  Morphology,  Part  I,  p.  254. 

2  Ibid.  p.  257. 


314  CAUSES  OF  VARIATION 

Acclimatization  to  electricity.  It  is  matter  of  common  knowl- 
edge that  individuals  working  about  electricity  and  accustomed 
to  frequent  shocks  acquire  a  high  resistance  power.  Exact  data 
are  not  at  hand,  but  of  the  general  fact  there  can  be  no  doubt. 

Acclimatization  in  general.  It  is  matter  of  common  experience 
that  among  the  higher  animals  and  plants  extreme  changes  in 
locality  may  be  followed  by  any  one  of  three  separate  conse- 
quences :  first,  unprecedented  prosperity  from  extremely  suit- 
able conditions, — conditions  even  more  favorable  than  in  the 
native  habitat ;  second,  absolute  failure  from  sheer  inability  to 
endure  the  changed  conditions ;  and  third,  a  period  of  struggle, 
followed  by  a  more  or  less  complete  adaptation  to  new  condi- 
tions, —  a  process  known  everywhere  as  acclimatization. 

The  known  facts  concerning  adaptation  in  lower  forms  seem 
to  apply  in  the  same  direction,  if  not  to  the  same  extent,  to 
even  the  highest  known  species.  For  example,  the  biennial  of 
the  temperate  regions  becomes  perennial  in  the  tropics,  where 
all  distinctions  of  this  order  blend  and  disappear  and  where  all 
plants  live  until  they  die  from  other  than  climatic  causes.  This 
is  a  sufficient  explanation  for  the  more  ready  formation  of  fleshy 
roots  and  stems  in  northern  regions,  and  the  lesser  storage  of  food 
reserves  in  the  tropics,  where  growth  tends  to  be  continuous. 

It  has  always  been  held  that  plants  have  higher  powers  of 
acclimatization  than  have  animals.  Doubtless  this  is  true,  at 
least  so  far  as  purely  climatic  conditions  are  concerned,  because 
animals,  being  free  to  move  and  gifted  with  more  or  less  intelli- 
gence, are  able  in  a  considerable  degree  to  avoid  the  full  effects 
of  climate  by  seeking  shelter  or  protection  of  some  sort.  Their 
own  bodies  are  fitted  to  maintain,  even  against  fearful  odds,  a 
nearly  constant  temperature.  So  far  as  temperature  is  concerned, 
therefore,  animals  do  not  need  the  same  degree  of  adaptation  as 
do  plants,  which  must  endure  the  best  they  can  the  "  accident  of 
position."  Whether  the  animal  possesses  the  same  capacity  for 
acclimatization,  whether  it  is  capable  of  undergoing  the  same  de- 
gree of  alteration  and  developing  the  same  resistance,  is  another 
question,  but  experience  with  poisons  tends  to  show  that  the  animal 
organism  is  not  inferior  to  the  vegetable  in  point  of  adaptability 
when  put  to  the  actual  test  and  compelled  to  face  the  inevitable. 


RELATIVE  STABILITY  OF  LIVING  MATTER 


315 


Space  does  not  permit  the  enumeration  of  instances  of  acclima- 
tization of  domesticated  animals  and  plants.  References  are  full 
of  data  of  this  sort,  and  common  experience  supplies  a  mass 
of  additional  information.  That  both  animal  and  plant  species 
possess  and  exercise  large  powers  of  adaptation  to  external  condi- 
tions is  now  no  longer  questioned.  The  only  doubt  is  as  to  the 
method.  Whether  the  whole  effect  is  produced  through  individ- 
ual modification,  whether  it  is  largely  the  result  of  selection  of 
hardier  strains,  or  whether  there  is  some  inheritance  of  modifica- 
tion of  this  sort  is  yet  an  open  question. 

Without  a  doubt  individual  modification  has  been  underesti- 
mated. It  has  been  said  that  the  powers  of  individual  adaptation 
are  slight  and  that  real  acclimatization  is  secured  through  the 
selection  of  the  few  individuals  naturally  endowed  with  powers 
of  high  resistance.  For  example,  it  is  a  well-known  fact  that 
when  an  entire  field  of  corn  (maize)  has  suffered  from  a  killing 
frost  a  few  stalks  here  and  there  are  unaffected.  The  same  fact 
has  been  noted  among  garden  vegetables  and  fruits  of  various 
sorts,  many  of  which  are  mentioned  by  Darwin.1  In  changing 
spring  to  winter  wheat  all  but  a  few  stalks  are  killed  the  first 
winter,  but  those  remaining  give  rise  to  winter  strains. 

These  and  similar  facts  have  given  rise  to  the  idea  that  accli- 
matization is  really  through  the  selective  process,  and  based  on 
inherent  differences  in  constitution  of  the  organism  rather  than 
upon  adaptability.  Recent  researches,  however,  have  shown, 
within  limits,  an  unexpected  degree  of  adaptability  in  the  individ- 
ual, and  the  examples  already  cited  establish  the  fact  that  acclima- 
tization is  largely  the  result  of  modification  of  protoplasm.  How 
far  this  modification  is  possible  and  how  far  it  is  permanent,  and 
whether  it  is  in  any  degree  inherited,  are  now  the  absorbing 
questions.  That  there  is  a  high  degree  of  permanence,  at  least 
in  some  cases,  is  well  established.  Whether  the  modifications  are 
to  any  extent  inherited  is  a  subject  that  will  be  discussed  in  the 
next  chapter. 

Two  facts  are  worthy  of  note  in  all  studies  in  acclimatization : 
first,  the  variations  are  functional,  not  morphological ;  second, 
the  external  forces  involved  are  such  as  exercise  an  all-pervading 

1  Darwin,  Animals  and  Plants  under  Domestication,  II,  299-300. 


316  CAUSES  OF  VARIATION 

influence.  Heat,  chemical  action,  light,  electricity,  —  all  are  in- 
fluences that  penetrate  to  the  very  constitution  of  the  proto- 
plasm, even  of  the  germ  perhaps.  The  most  significant  biological 
fact  in  these  studies  is  the  wide  range  of  adaptation  and  the 
exceedingly  diverse  conditions  under  which  living  matter  may 
continue  to  discharge  its  normal  functions,  —  either  unaltered  or 
but  slightly  modified,  —  and  the  next  most  significant  fact  is  the 
more  or  less  permanent  alteration  in  functional  activity  through 
changed  conditions  of  the  order  mentioned.1 

SECTION    VII  —  EVIDENCE    FROM    REGENERATION 

All  animals  and  plants  have  more  or  less  power  to  restore  lost 
or  injured  parts.  It  is  noticeable,  and  perhaps  significant,  that 
the  power  of  regeneration  is,  roughly  speaking,  in  inverse  ratio 
to  the  degree  of  differentiation ;  that  is  to  say,  lower  organisms 
have,  in  many  cases  at  least,  almost  unlimited  powers  of  regenera- 
tion, while  among  the  highest  species  the  ability  to  restore  lost 
parts  is  very  slight. 

The  bearing  of  this  matter  upon  the  question  in  hand  —  the 
relative  stability  or  instability  of  living  matter —  is  of  course  not 
in  \h&fact  of  regeneration  but  in  the  character  of  the  regenerated 
part  as  compared  with  the  original,  and  in  the  general  behavior 
of  the  organism  when  occasion  for  regeneration  arises.  Most  of 
the  instances  given  in  this  connection  are  drawn  from  Morgan's 
excellent  work,  Regeneration. 

Regeneration  in  animals.2  Trembley  (1740),  Reaumur  (1742), 
Bonnet  (1745),  and  Spallanzani  (1768)  were  early  investigators 
in  this  subject.  Their  experiments  have  been  often  repeated  and 
their  observations  extended  until  the  field  has  been  well  worked 
and  the  limits  of  regeneration  fairly  well  established. 

If  the  foot  of  a  salamander  be  cut  off  a  new  one  regenerates.  If 
the  entire  leg  be  removed  it  regenerates,  and  at  whatever  point  the 

1  For  additional  references  on  acclimatization  see    Darwin's  Origin  of   Spe- 
cies, and  his  Animals  and  Plants   under  Domestication,  II,  295-305  ;  Vernon, 
Variation  in  Animals  and  Plants,   pp.  379-387 ;  Bailey,  Survival  of  the  Unlike 
(second  edition),  pp.  307,  310,  320  ;   Weismann,  Studies  in  the  Theory  of  Descent, 
pp.  555-622  ;  Morgan,  Evolution  and  Adaptation,  pp.  319-325. 

2  Morgan,  Regeneration,  pp.  i-io. 


RELATIVE  STABILITY  OF  LIVING  MATTER        317 

cut  is  made  regeneration  begins  at  that  point  and  completes  the 
part.  Spallanzani  reports  that  all  four  legs  and  the  tail  of  a  sala- 
mander were  removed  as  many  as  six  times  within  three  months, 
and  were  regenerated  each  time,  —  as  promptly  the  last  time  as 
the  first.  He  calculated  that  in  all  647  new  bones  were  formed. 

This  shows  that  regeneration  not  only  begins  at  the  proper 
point,  but,  in  some  cases  at  least,  is  capable  of  indefinite  repeti- 
tion. The  restored  part  is  at  first  smaller  than  the  normal,  but  it 
continues  to  grow  until  the  proper  size  is  reached,  when  it  stops. 

If  a  part  of  the  jaw  of  the  salamander  be  cut  off  it  is  restored, 
or  if  a  part  of  the  eye  be  removed  it  regenerates  ;  but  if  the  en- 
tire eye  or  the  leg,  "  including  the  shoulder  girdle,"  be  removed, 
neither  is  regenerated.  A  lizard  can  regenerate  its  tail,  but  not 
its  limbs,  while  most  vertebrates  can  regenerate  neither. 

If  the  tail  of  a  fish  be  cut  off  near  the  base,  it  will  be  restored 
to  its  original  form,  no  matter  whether  the  cut  be  square  or 
oblique.  Not  only  that,  but  the  rapidity  of  growth  will  not  be 
uniform  at  all  points  along  the  cut  surface.  The  points  at  which 
the  growth  will  be  most  rapid  depend  upon  two  considerations, 
—  the  original  form  of  the  tail  (whether  bilobed  or  otherwise), 
and  the  direction  of  the  cut  (whether  square  or  oblique).  It 
will  be  more  rapid  at  the  points  where  most  is  to  be  restored 
(see  Fig.  35). 

On  this  point  Morgan  very  pertinently  remarks  that  "  the 
point  of  special  interest  is  that  the  new  material  that  appears 
over  the  exposed  edge  does  not  first  grow  out  at  an  equal  rate 
at  all  points  until  it  reaches  the  level  of  the  original  fork  (in  a 
bilobed  tail),  and  then  continue  to  grow  in  two  regions,  to  form 
the  lobes  of  the  tail,"  but  the  object  is  accomplished  by  differ- 
ences in  the  rate  of  growth,  and  the  "  regions  of  most  rapid 
growth  are  very  soon  established  in  the  new  tail." 

Extensive  experiments  in  regeneration  among  earthworms 
have  been  conducted,  not  only  by  Trembley  and  Bonnet  upon 
Lumbriculus,  but  later  by  Morgan  upon  Allolobophora  foetida? 

From  these  investigations  it  appears  that : 

i .  If  in  the  last-named  species  one  segment  of  the  head  be  cut 
off,  it  is  promptly  restored  (see  Fig.  36,  B). 

1  Morgan,  Regeneration,  pp.  7,  8  ;  also  Fig.  35  of  this  book.        2  Ibid.  pp.  3-10. 


CAUSES  OF  VARIATION 


2.  If  two  or  if  three  segments  be  cut  off,  an  equal  number  will 
be  restored  (see  Fig.  36,  C,  D). 

3.  If  four  or  five  be  cut  off,  generally,  but  not  always,  a  corre- 
sponding number  come  back  (see  Fig.  36,  E,  F). 

i 


B 


G 


FIG.  35.    The  method  of  growth  in  regeneration 


A,  tail  of  Fundulus  heteroclitus :  cut  squarely,  it  regenerates  as  at  B ;  cut  obliquely,  as  at  C. 
In  D  and  E  are  shown  regeneration  from  two  oblique  cuts ;  G,  tail  of  stenopus,  regen- 
erating from  square  cut  at  //and  from  oblique  cut  at  /.  —  After  Morgan 

4.  If  six  or  more  be  cut  off,  only  four  or  five  come  back. 
These  are  the  segments  constituting  the  head  proper,  all  of  which 
are  restored  ;  but  if  the  cut  be  made  farther  back,  the  intermediate 


RELATIVE   STABILITY   OF   LIVING   MATTER 


319 


segments  are  not  restored,  "and  the  worm  remains  shortened 
throughout  the  rest  of  its  life  "  (see  Fig.  36,  G,  H). 


G  H 

FIG.  36.    Regeneration  of  earthworm,  Allolobophora  fa-tida 

A,  normal  worm ;  B-F,  regeneration  after  removal  of  one,  two,  three,  four,  and  five  head 
segments  respectively;    G,  anterior  third  cut  off,  only  five  segments  restored;    //,  cu 
in  two  in  the  middle,  only  five  restored;   /,  cut  posterior  to  the  middle,  tatl  m 
restored.  —  After  Morgan 

5.  If  the  cut  be  far  enough  back  to  remove  the  reproductive 
organs,  they  are  never  reformed,  "  and  the  worm  remains  inca- 
pable of  reproducing  itself." 


320  CAUSES   OF   VARIATION 

6.  If  the  cut  be  made  beyond,  that  is  posterior  to,  the  middle, 
both  parts  will  regenerate.   The  posterior  part,  however,  will  re- 
generate slowly  and  with  difficulty,  not  head,  but  tail  segments, 
and  the  anomaly   arises   of  an  earthworm  with   two  tails  and 
no  head.    There  is  thus  a  kind  of  "polarity"  by  which  anterior 
segments  may  arise  only  from  comparatively  anterior  regions, 
and  by  which  posterior  regions  must  of  necessity  give  rise  to 
posterior  segments.    The  same  significant  facts  are  notable  in 
other  species,  both  animal  and  plant  (see  Fig.  36,  /). 

7.  "  This  same  relation  between  the  number  of  segments  cut 
off  from  the  anterior  end  and  the  number  that  is  regenerated 
seems  to  hold  good  throughout  the  whole  group  of  annelids, 
although  the  maximum  number  that  comes  back  may  be  differ- 
ent in  different  species.    Thus  in  Lumbriculus  six,  seven,  or 
even  eight  new  segments  come  back,  if  more  than  that  number 
are   removed."1    There  is  therefore   a  definite   termination  to 
the  power  of  regeneration,  even  in  species  with  high  regener- 
ating powers. 

8.  "  If  we  examine  the  method  of  regeneration  from  the  pos- 
terior end  of  a  piece  of  an  earthworm,  we  find  that  when  several 
or  many  posterior  segments  have  been  removed  a  new  part  comes 
back,  composed  at  first  of  very  few  segments,"2  the  last  of  which 
contains  the  new  opening  for  the  digestive  tract.    Later  addi- 
tional segments  are  formed  just  ahead  of  the  last  segment,  quite 
after  the  normal  manner  of  increasing  the  length  in  many  species 
of  annelids, 

9.  The  anterior  portion  does  not  possess  the  power  of  regen- 
eration unless  it  consists  of  a  considerable  number  of  segments 
(see  Fig.  37,  A-E). 

10.  If  a  short  piece  (three  to  seven  segments)  of  the  anterior 
portion  of  one  worm  be  grafted  in  a  reversed  position  upon  the 
anterior  end  of  another  worm,  trie  grafted  part  will  regenerate  a 
head  of  about  two  segments  from  its  free  end,  which  was  origi- 
nally the  posterior  extremity,  but  of  an  anterior  piece  (see  Fig. 
37,  F).  This  shows  the  entire  power  of  reversal  as  to  relative 
position  of  segments,  —  a  high  degree  of  adaptability. 

1  Morgan,  Regeneration,  p.  9. 

2  Ibid.  p.  9. 


RELATIVE   STABILITY   OF   LIVING   MATTER 


Of  the  flat  worms,  the  fresh-water  planarians  have  remarkable 
powers  of  regeneration. 

i.  If  the  worm  be  cut  in  two  at  any  point,  each  piece  regen- 
erates. If  at  or  near  the  middle,  two  complete  worms  result, 
though  at  first  smaller  than  the  normal. 


FIG.  37.    Regeneration  of  head  ends  of  Allolo- 
boph  or  a  fcetida 

A,  B,  too  short  for  regeneration;  C-E,  longer  anterior 
pieces  that  made  new  segments;  F  (after  Hazen),  a 
piece  of  five  anterior  segments  grafted  in  a  reversed  - 
position  upon  the  anterior  end  of  another  worm  (note  a 
heteromorphic  head  of  two  segments  regenerated  from 
the  free,  which  is  the  posterior,  end).  — After  Morgan 


2.  If  the  cut  be  very  near  the  head,  the  main  por- 
tion will  of  course  regenerate  perfectly,  but  the  piece 
removed  will  regenerate  a  reversed  head,  and  the 
anomaly  results  of  a  piece  with  a  head  on  either  end  but  no  body 
(see  Fig.  38,  F). 

3.  If  a  piece  be  removed  from  the  middle  by  transverse  ( 
each  part  regenerates  and  three  worms  result. 


322 


CAUSES  OF  VARIATION 


Lateral  regeneration.  All  examples  thus  far  given  are  of  regen- 
eration lengthwise,  and  of  the  restoration  of  parts  similar  to  those 
removed,  but  arising  from  matter  differently  differentiated. 

If  the  planarian  be  split  lengthwise,  either  through  the  middle 
or  well  to  one  side,  each  piece  will  regenerate.  If  a  hydra  be 


U 


\J 


\J 


FIG.  38.    Regeneration  in  the  planarian 

/4,  normal  worm;  B,  Bl,  regeneration  of  anterior  half ;  C,  C1,  regeneration  of  posterior  half ; 
D,  crosspiece  out  of  middle ;  Z>1,  Z>2,  D%,  D4,  regeneration  of  same ;  £,  old  head ;  El, 
E2,  E*,  regeneration  of  same ;  F,  old  head  cut  off  just  behind  the  eyes ;  P*t  regeneration 
of  new  head  on  posterior  end  of  same.  —  After  Morgan 

split,  the  edges  of  the  tube  will  come  together  and  join,  making 
a  tube  of  smaller  diameter,  enlarging  later.  If  the  leg  of  a  sala- 
mander be  split  and  a  part  removed,  it  will  be  replaced,  showing 
that  regeneration  is  lateral  as  well  as  longitudinal. 

If,  however,  the  body  of  the  salamander  should  be  split,  both 
pieces  would  die,  not  primarily  from  lack  of  regenerating  powers 


RELATIVE   STABILITY   OF   LIVING   MATTER 


323 


but  from  sheer  inability  to  support  life.  Manifestly  all  regener- 
ation is  a  struggle,  and  a  prerequisite  to  its  accomplishment  is 
an  assured  base  of  supplies  and  uninjured  vital  organs. 

Regeneration  by  transformation.1  Regeneration  in  some  of 
the  lower  animals  is  accomplished  through  rearrangement  of  old 
substance  as  well  as  through  the  addition  of  new  material. 


FIG.  39.    Regeneration  of  Stentor  cut  into  three  pieces,  as  at  A 

B :  this  row  shows  regeneration  of  anterior  piece.  C:  this  row  shows  regeneration  of  middle 
piece.  D  :  this  row  shows  regeneration  of  posterior  piece.  This  regeneration  is  effected 
first  of  all  by  rearrangement  of  material,  —  each  piece  having  been  supplied  with  a  por- 
tion of  the  nucleus. —  After  Morgan,  from  Gruber 

If  a  short  piece  be  cut  from  the  stem  of  a  hydra  the  first  step 
in  the  formation  of  a  new  individual  from  the  piece  is  the  closing 
of  the  ends  and  a  shrinking  of  diameter,  thus  making  a  closed  cylin- 
der, but  much  smaller  than  the  stem  from  which  it  was  cut.  In 
a  day  or  two  four  tentacles  appear  at  one  end,  and  shortly  the 
piece  has  assumed  the  characteristic  form  and  proportions  of  a 
complete  hydra,  after  which  it  may  increase  in  size.  The  same 
is  true  of  a  piece  of  a  planarian  or  of  a  Stentor  (see  Fig.  39). 

1  Morgan,  Regeneration,  pp. 


324  CAUSES  OF  VARIATION 

The  first  process  seems  to  be  to  assume  the  characteristic 
form,  afterward  to  increase  in  size  ;  not  only  that,  but  regenera- 
tion is  possible  in  the  entire  absence  of  food,  as  will  be  seen 
later,  —  all  of  which  indicates  a  more  or  less  extensive  transfor- 
mation of  material. 

Regeneration  in  embryos  and  eggs.1  There  is  much  reason  to 
believe  that  regeneration,  especially  by  rearrangement,  is  more 
pronounced  in  the  embryonic  than  in  the  adult  state.  The  frog 
does  not  regenerate  the  leg,  but  the  tadpole  does.  If  the  blastula 
of  the  sea  urchin  be  cut  into  two  pieces,  each  will  develop  into  a 
perfect,  but  abnormally  small,  embryo.  If  the  parts  be  separated 
at  the  two-  or  the  four-celled  stage,  each  is  capable  of  developing 
into  a  perfect  embryo,  but  at  the  eight-celled  stage  they  are  not 
capable  of  such  development. 

If  each  cell  of  the  two-celled  stage  is  capable  of  developing 
into  a  complete  individual,  then  the  material  at  this  stage  must 
be  indifferent,  that  is  undifferentiated.  In  other  words,  if  the 
first  cleavage  be  considered  as  dividing  into  right  and  left  halves, 
and  each  half  is  capable  of  developing  into  a  whole,  the  case  is 
exactly  like  that  of  regeneration  in  the  split  planarian  ;  if,  how- 
ever, the  first  segmentation  be  considered  as  dividing  into  ante- 
rior and  posterior  regions,  and  if  each  may  develop  an  individual, 
it  is  exactly  similar  to  the  case  of  the  regeneration  of  a  worm 
that  has  been  cut  in  two  crosswise  into  anterior  and  posterior 
halves.  In  all  cases  some  readjustment  of  material  is  involved. 

This  separation  is  easily  effected  in  the  sea  urchin  by  shaking, 
in  which  case  each  part,  below  the  eight-celled  stage,  develops  an 
individual.  If  in  the  frog  the  parts,  even  at  the  two-celled  stage, 
be  separated,  each  collapses  ;  if  instead  one  half  be  killed  by  a 
needle,  the  uninjured  part  develops  at  first  a  half  embryo,  after- 
wards making  more  or  less  successful  "post  generation"  of  a 
whole  embryo.2  It  is  therefore  a  perfectly  well-establrshed  fact 
that,  in  certain  species  at  least,  a  part  of  an  egg  or  embryo  is 
capable  of  developing  into  a  perfect  individual. 

To  what  extent  this  separation  of  segmenting  eggs  at  the 
two-celled  stage  may  take  place  in  nature  is  of  course  unknown, 

1  Morgan,  Regeneration,  p.  18;  also  chap,  xi,  pp.  216-241. 

2  Ibid.  pp.  216-221. 


RELATIVE   STABILITY   OF   LIVING   MATTER         325 

but  it  has  been  assumed  to  be  the  cause  of  the  production  of 
such  twins  as  are  exceedingly  similar.  Hypothetical  cases  of  this 
sort  are  known  as  "identical  twins,"  supposedly  arising  from  a 
single  ovum  instead  of  from  two. 

Experiments  upon  a  variety  of  species  show  different  powers 
of  development  from  part  embryos.  Wilson  found,  and  Morgan 
verified  the  fact,  that  in  Amphioxus  each  of  the  first  two  or  four 
cells  could  develop  an  entire  embryo,  and  that  the  one  to  eight 
blastomeres  would  develop  to  the  blastula  stage  but  no  farther. 
Zoja  showed  that  the  isolated  blastomeres  in  a  number  of  jelly- 
fish developed  each  a  whole  embryo  but  of  small  size.1  Driesch 
studied  the  matter  in  ascidians  and  found  the  cleavage  of  iso- 
lated blastomeres  to  be  neither  like  that  of  the  whole  embryo 
nor  like  the  development  they  would  each  have  undergone  had 
they  remained  in  place.  They  produce  symmetrical  gastrulae 
and  larvae  of  small  size,  but  lacking  in  certain  parts? 

No  one  can  avoid  the  conclusion  that  the  phenomena  of  re- 
generation generally  show  an  extreme  stability  of  living  mat- 
ter ;  but  they  also  betray,  especially  in  lower  organisms  and  in  the 
developing  embryo,  an  unexpected  elasticity.  To  assign  absolute 
stability  or  extreme  instability  to  living  matter  would  be  to  state 
but  half  the  truth.  A  fair  interpretation  of  the  facts  of  regen- 
eration leads  to  the  conviction  that  living  matter  has  the  power 
of  extreme  readjustment  in  its  effort  to  discharge  its  normal  func- 
tions, and  that  it  will  discharge  those  functions  as  nearly  as  may 
be,  even  under  dire  distress,  and  even  though  important  details 
of  structure  are  by  force  omitted. 

Regeneration  in  plants.  This  is  different  from  regeneration 
in  animals  in  that  "  the  piece  does  not  complete  itself  at  the  cut 
end,  nor  does  it  change  its  form  into  that  of  a  new  plant,  but 
the  leaf  buds  that  are  present  on  the  piece  begin  to  develop, 
especially  those  near  the  distal  end  of  the  piece."  3  The  processes 
are  similar  in  the  two  cases  in  that  a  piece  may  give  rise  to  a 
whole  individual,  as  when  the  begonia  leaf  throws  out  first  roots 
and  then  stems,  which  develop  into  perfect  plants. 

Regeneration  in  higher  animals.  It  is  a  somewhat  singular  fact 
that  the  lower  animals  possess  larger  powers  of  regeneration  of  lost 

1  Morgan,  Regeneration,  p.  237,  2  Ibid.  p.  236.  8  Ibid.  p.  15. 


326  CAUSES  OF  VARIATION 

parts  than  do  those  which  are  more  highly  differentiated.  Still 
the  latter  are  not  destitute  of  this  faculty  of  replacement.  The 
teeth  of  many  vertebrates  are  shed  once  and  replaced ;  rarely  a 
second  replacement  occurs.  If  the  ox  loses  the  horn,  the  loss  is 
permanent ;  but  the  stag  sheds  his  annually,  each  successive  pair 
arising  from  the  same  scar  or  bud,  but  each  provided  with  an 
additional  prong.  By  what  inherent  quality  of  this  particular 
spot  are  we  to  explain  this  annual  change  in  the  character  of 
the  part  restored  ? 

Birds  shed  their  plumage,  and  many  animals  their  hair,  annu- 
ally, as  trees  shed  their  leaves,  and  often  the  new  growth  dif- 
fers materially  from  the  old.  The  "  milk  teeth  "  are  simpler  than 
the  permanent  set ;  the  color  of  the  foal  and  the  fawn  changes 
with  maturity ;  and  the  shape  of  the  cotyledon  gives  little  indi- 
cation of  what  the  real  leaf  will  be.  Nobody  seeing  the  umbrella- 
like  first  leaf  of  the  basswood  would  suspect  what  the  later 
leaves  will  be,  nor  would  one  suspect  the  clover  until  the  "  third 
leaf  "  appears. 

Repair  of  injury  among  higher  animals  seems  to  be  exceed- 
ingly limited.  However,  wounded  muscles  can  "  fill  up  "  to  some 
extent ;  cut  nerves  mend  slowly ;  severed  blood  vessels  repair 
themselves  and  restore  circulation  to  the  part ;  liver,  kidney, 
glands,  and  tissues  generally  have  sufficient  power  of  regenera- 
tion to  close  wounds  and  to  replace  lost  portions  more  or  less 
perfectly,  but  nearly  always  with  a  scar  ;  broken  bones  will  knit 
or  a  small  piece  removed  will  be  restored,  but  an  entire  bone  cut 
off  will  not  be  replaced.  Of  all  parts  the  skin  possesses  the  highest 
power  of  restoration,  probably  because  it  is  normally  in  active 
growth  from  beneath  to  replace  the  parts  worn  off  from  above. 

The  character  of  the  regenerated  part.  The  regenerated  part 
may  compare  with  the  original  in  any  one  of  four  different  ways  : 

1.  It  may  be  exactly  like  the  original,  as  in  the  leg  of  a  sala- 
mander (holomorphosis). 

2.  It  may  be  like  the  original  except  smaller  in  size  (mero- 
morphosis). 

3.  It  may  be  different  from  the  original  but  like  some  other 
part  of  the  body,  as  when  an  antenna  replaces  an  eye  (hetero- 
morphosis). 


RELATIVE  STABILITY  OF  LIVING  MATTER        327 

4.  It  may  be  unlike  any  normal  structure  of  the  body,  as  when 
a  new  leg  is  "  unlike  any  other  leg  on  the  body"1  (neomorphosis). 

With  respect  to  the  tissues  from  which  regenerated  parts  arise 
two  distinct  cases  are  to  be  noted  : 

1.  Where  the  part   regenerated  springs  from  tissue  of  the 
same  kind,  requiring  only  an  extension  of  growth,  as  when  an 
injured  muscle  is  repaired. 

2.  Where  the  regenerated  part  springs  from  tissue  of  a  totally 
different  order,  as  where  a  severed  leg  is  restored  from  the  cut 
outward,  or  where  the  lens  of  an  eye  arises  from  the  iris,  re- 
quiring differentiation  as  well  as  growth.2     This  subject  will  be 
pursued  further  under  the  section  on  "  Origin  of  New  Cells  and 
Tissues." 

Effect  of  temperature  upon  regeneration.3  Planarians  were  cut 
in  two  transversely  at  the  pharynx.  No  regeneration  took  place 
below  3°  C.  Of  six  specimens  kept  at  this  temperature  only 
one  regenerated,  and  that  incompletely,  the  eyes  and  brain 
being  incomplete  after  six  months.  The  temperature  at  which 
regeneration  took  place  most  rapidly  was  29.7°,  at  which  a  new 
head  formed  in  four  and  six-tenths  days.  At  31.5°  it  required 
eight  and  a  half  days  to  complete  the  head ;  at  32°  regeneration 
commenced,  but  death  occurred  in  about  six  days;  at  33°  re- 
generation was  slight,  and  at  34°  none  took  place,  death  occur- 
ring within  three  days.  Other  species  showed  a  similar  range 
for  optimum,  minimum,  and  maximum.4 

Influence  of  food  upon  regeneration.5  While  regeneration  takes 
place  more  rapidly  with  a  full  food  supply,  it  nevertheless  pro- 
ceeds without  it.  In  this  case  the  new  growth  appears  to  be  de- 
rived not  from  surplus  food  material  but  from  the  protoplasm 
itself,  resulting  in  reduction  in  size. 

If  a  planarian  be  kept  for  several  months  without  food,  in 
this  starved  condition  it  gradually  shrinks  in  size,  even  to  one 
thirteenth  of  the  normal  (see  Fig.  40). 

If  a  starved  worm  be  cut  in  two  pieces,  each  will  regenerate, 
though  more  slowly  than  if  fed,  the  new  part  increasing  in  size 
at  the  expense  of  the  old. 

1  Morgan,  Regeneration,  p.  24.  3  Ibid.  pp.  26-27.  5  Ibid.  pp.  27-29. 

2  Ibid.  p.  205.  4  Ibid.  pp.  26-27. 


28 


CAUSES   OF  VARIATION 


As  Morgan  remarks,1  "  The  growth  of  the  new  part  at  the 
expense  of  the  old  tissues  is  a  phenomenon  of  the  greatest  im- 
portance, an  explanation  of  which  will  involve,  I  think,  the  most 
fundamental  questions  pertaining  to  growth."  To  this  remark  it 
may  be  added  that  the  phenomenon  is  also  of  the  greatest  impor- 
tance in  its  bearing  upon  the  relative  stability  of  living  matter. 
In  so  far  as  protoplasm  is  worked  over  to  serve  new  purposes,  it 
shows  wonderful  elasticity  ;  but  the  fact  that 
the  organism  preserves  or  completes  its  plan 
at  almost  any  expense,  even  to  itself,  betrays 
a  wonderful  persistence  on  the  part  of  the 
original  plan. 

It  is  known  that  the  starving  cat  or  dog 
will  replace  a  large  share  of  the  dry  matter 
of  the  body  with  water,  and  sacrifice  all  other 
activities  to  the  vital  processes.  Plants  grow- 
ing with  no  nitrogen  supply  save  what  is 
contained  in  the  seeds  will  soon  reach  the 
maximum  of  possible  development,  but  will 
continue  to  produce  new  leaves  at  the  ex- 
pense of  the  old  ones,2  as  the  rapidly  grow- 
ing stalk  of  the  century  plant  feeds  on  its 
thickened  leaves,  or  the  beet  and  carrot  feed 
on  their  thickened  roots. 

Effects  of  light  upon  regeneration.3   In  the 

same    individual    after     cage  Qf  plants  only  4  ^OeS  light  Seem  to  affect 
being  kept  without  food  » 

for  four  months  and  regeneration,  and  iri  them  the  influence 
appears  to  be  confined  to  the  blue  rays. 
"  Herbst  observed  that  when  the  eye  of  cer- 
tain Crustacea  is  cut  off,  sometimes  an  eye  and  sometimes  an 
antenna  is  regenerated."  Experiments  were  conducted  to  see 
whether  light  might  be  the  factor  which  determined  whether  the 

1  Morgan,  Regeneration,  pp.  27-29. 

2  The  writer  saw  the  original  clover  plants  in  the  first  Rothamsted  series  for  test- 
ing the  nitrogen-gathering  powers  of  root  tubercles.    One  of  these  plants  had  no 
source  of  nitrogen  but  the  seed.    It  was  two  years  old,  still  producing  new  leaves 
as  the  old  ones  died  down,  but  it  had  never  blossomed,  nor  was  it  able  to  pro- 
duce more  than  four  leaves  at  any  time. 

3  Morgan.  Regeneration,  pp.  29-30.  4  Ibid.  p.  78. 


FIG.  40.  Effect  of  star- 
vation upon  the  pla- 
in arian 

A,  well-fed  worm ;  ff,  the 


thirteen    days.  —  After 
Morgan 


RELATIVE  STABILITY  OF   LIVING  MATTER        329 

eye  or  the  antenna  should  appear,  but  as  many  eyes  were  regener- 
ated in  the  dark  as  in  the  light.  It  was  found,  however,  by  both 
Herbst  and  Morgan  independently,  that  "when  the  end  only  of 
the  eyestalk  is  cut  off  an  eye  regenerates,  but  when  the  eyestalk 
is  cut  off  at  the  base  an  antenna  regenerates."  1 

Effect  of  gravity  upon  regeneration.  The  effect  of  gravity  upon 
regeneration  in  plants  is  pronounced,2  but  only  one  case  is  known 
of  its  influence  upon  regeneration  in  animals.  This  is  the  case  of 
the  hydroid  Antennularia  antennina? 

This  animal,  however,  has  many  of  the  characteristics  of  the 
plant,  for  it  lives  attached  by  a  kind  of  root  to  the  bottom  of 
the  sea,  and  its  general  form  is  that  of  a  branching  stem,  like  a 
typical  plant.  All  experiments  show  that  regeneration  in  this 
form  is  always  with  reference  to  gravity,  much  as  in  the  case  of 
plants.  Whatever  the  position  of  the  piece,  the  new  growth  is 
upward  from  the  most  elevated  part,  whether  basal  or  apical,  and 
downward  from  the  lower  extremity  and  from  the  base  of  the 
new  growth  (see  Fig.  41). 

The  effect  of  gravity  upon  regeneration  in  plants  may  be 
briefly  summarized  as  follows  :  4 

1.  If  a  piece  of  stem  of  the  willow  be  suspended  with  its 
apex  upward,  in  three  or  four  days  roots  will  spring  from  small 
swellings  at  the  basal5  end,  and  three  or  four  buds  will  arise  at 
the  apical  5  end,  the  one  at  the  extreme  tip  coming  first  and  grow- 
ing fastest,  others  in  regular  decreasing  order  (see  Fig.  26,  A). 

2.  If  the  piece  is  long  the  lower  buds  will  not  start,  but  if  it 
should  be  cut  in  two  pieces,  or  if  a  ring  of  bark  should  be  cut  from 
the  middle,  each  would  behave  as  already  described,  showing 
that  any  point  on  the  stem  may  throw  out  either  shoots  or  roots, 
according  to  its  position  with  reference  to  the  cut  and  to  gravity. 

3.  These  new  growths  generally  arise  from  preexisting  buds 
if  the  piece  is  young,  but  they  may  arise  from  regions  entirely 
destitute  of  preexisting  buds.    The  writer  knew  a  red  maple  tree 

1  Morgan,  Regeneration,  p.  30.  2  Ibid.  pp.  71-80.  8  Ibid.  pp.  30-32. 

4  The  pieces  experimented  upon  were  suspended  in  moist  atmosphere. 

*  In  all  these  explanations  "basal"  means  the  end  that  was  down  whe 
plant  was  in  its  normal  position,  whatever  its  position  during  the  exper 
"Apical"  refers  to  the  end  farthest  from  the  base  in  nature. 


330 


CAUSES  OF  VARIATION 


in  Urbana,  Illinois,  eighteen  inches  or  more  in  diameter.  It 
forked  about  six  feet  from  the  ground.  A  heavy  storm  split 
one  of  the  limbs  away,  when  it  was  found  that  a  dense  net- 
work of  roots  had  formed  in  the  moist  soil  that  had  collected 
in  the  fork. 


FIG.  41.  Regeneration  in  response  to  gravity  in  animal  organisms  :  this  creature 
(Antennularia  antennina)  resembles  plants  in  its  habit  of  growth,  being 
attached ;  it  also  resembles  them  in  its  response  to  gravity  in  regeneration. 
—  After  Morgan,  from  Loeb 

4.  If  the  piece,  be  suspended  apex  down,  the  shoots  will  still 
start  from  the  apical  end,  bending  upward,  and  roots  will  start 
not  only  from  the  basal  end,  now  uppermost,  but  they  will  start 
from  the  whole  length  of  the  stem  and  bend  downward,  showing 
that  the  force  determining  whether  shoot  or  root  shall  be  put  out 


RELATIVE   STABILITY  OF   LIVING  MATTER 


331 


is  largely  internal,  but  that  the  influence  determining  the  direc- 
tion of  the  growth  is  external,  —  gravity  (see  Fig.  26,  B). 

5.  This  "  polar  difference  "  is  most  energetic  in  j^flg-s terns, 
gradually  lessening  in  older  growth,  though  the  tendency  remains 
in  quite  old  pieces. 

6.  If  internodes  only  are  used,  some  plants  will  regenerate 
and  others  will  not ;  but  if  they  do  regenerate,  the  tendency  is 
for  roots  to  appear  from  the  basal  end  and  leaves  from  the  apical, 
whatever  the  position.1 

7.  If  a  piece  of  the  root  of  a  poplar  be  suspended  vertically  in 
a  moist  chamber,  apex  downward,  leaves  and  shoots  will  appear 
from  the  basal?  now  the  upper,  end ;   if  suspended  basal  end 
downward,  the  shoots  will  still  arise  from  this  (basal)  end.3 

8.  Certain  plants,  as  the  begonia,  are  able  to  produce  new 
plants  from  even  a  single  leaf'ii  set  in  moist  sand.    In  all  cases, 
so  far  as  known,  roots  first  arise  at  the  base  of  the  leaf  stem,  or 
midrib  section,  and  later  shoots  arise  on  the  apical  side  of  the 
roots,  whatever  the  position. 

9.  Curiously,  if  the  leaf  be  taken  from  a  begonia  just  ready 
to  flower,  the  new  plant  will  flower  very  quickly  after  becoming 
established,  but  with  few  leaves  and  little  growth ;  but  if  it  be 
taken  from  a  plant  just  out  of  flower,  the  growth  will  be  greater 
and  the  period  longer  before  flowering  follows. 

10.  When  pieces  of  stem  are  suspended  vertically,  apex  up- 
ward, polarity  and  gravity  act  together ;  when  suspended  apex 
downward  they  act  oppositely.    The  two  forces  may,  to  some 
extent,  be  separated  by  employing  different  positions.    For  ex- 
ample, if  the  piece  be  held  obliquely,  apical  end  the  higher,  the 
buds  along  the  upper  side  will  develop  more  than  those  on  the 
lower  side ;  and  if  it  be  placed  horizontally,  all  the  buds  on  what 
is  now  the  upper  side  of  the  stem  will  start,  but  those  at  the 
apical  end  will  grow  more  rapidly. 

If  held  in  an  oblique  position  with  basal  end  higher,  differ- 
ent results  follow  ;  but  in  general  it  is  shown  that  where  polarity 

1  Morgan,  Regeneration,  p.  74. 

2  It  should  be  remembered  that  the  basal  end  of  the  root  is  the  end  nearer 

the  stem. 

3  Morgan,  Regeneration,  p.  75. 


332 


CAUSES  OF  VARIATION 


and  gravity  are  opposed  to  each  other  the  former  is  by  far  the 
stronger  force.1 

ii.  If  a  long  piece  of  stem  be  suspended  by  both  ends,  roots 
will  start  freely  along  the  curved  lower  surf  ace  of  the  bent  stem. 
If  now  the  bent  stem  be  reversed,  roots  will  not  only  form  less 
freely,  but  they  will  mostly  be  along  the  lower  or  under  side  of 
the  arch,  the  concave  instead  of  the  convex  side  of  the  curve, 
and  clustered  closer  to  the  basal  end.2 

SECTION  VIII  — INTERNAL  FACTORS  IN  REGENERATION 

Even  among  plants  it  is  noticeable  that  internal  influences 
are  strongly  involved  in  the  regenerative  processes.  Indeed, 
one  point  of  difference  between  plants  and  animals  is  that  the 
latter  regenerate  directly  from  the  cut  surface,  while  the  former 
regenerate  by  means  of  buds  thrown  out  at  the  side  and  just 
behind  the  point  of  severance. 

Again,  it  is  to  be  observed  that  those  organisms  whose 
regeneration  is  influenced  by  gravity  are  the  attached  species, 
that  maintain  habitual  and  constant  relations  to  gravity,  but  that 
those  species  which,  like  most  animals,  move  about  freely, 
regenerate  according  to  internal  influences,  except  in  so  far 
as  vital  processes  are  involved  through  food,  temperature,  or 
chemical  conditions.  In  other  words,  the  study  of  regeneration 
is  essentially  a  study  of  internal  forces,  and  even  among  plants 
subject  to  the  influence  of  gravity  the  internal  factors  are  yet 
the  dominant  ones.  They  are  well  worth  study,  therefore,  as 
bearing  upon  the  subject  of  this  chapter  and  upon  the  inherent 
forces  of  organized  and  living  matter. 

Polarity  and  heteromorphosis.  If  a  short  piece  be  cut  from 
the  anterior  end  of  an  earthworm  the  main  piece  regenerates 
promptly,  the  small  piece  with  difficulty  or  not  at  all';  and  the 
same  is  true  as  to  the  posterior  end.  Again,  if  the  short  piece 
regenerate  at  all,  it  does  not  complete  itself  by  growing  a  new 
worm,  but  by  growing  a  reversed  head  (or  tail)  like  itself,  so 
that  we  may  have  an  individual  with  two  heads  and  no  tail,  or 
vice  versa.  In  other  words,  the  polarity  is  reversed  ;  for  if  the 

1  Morgan,  Regeneration,  p.  78.  2  Ibid.  pp.  79-80. 


RELATIVE   STABILITY   OF   LIVING   MATTER 


333 


worm  had  been  cut  in  the  middle,  both  halves  would  have  pro- 
duced an  entire  worm,  minus,  perhaps,  certain  parts  like  the 
reproductive  organs,  which  do  not  seem  to  be  reproduced.  How- 
ever, the  posterior  half  of  a  planarian  will  regenerate,  producing 
an  entire  worm  with  typical  eyes. 

What  it  is  that  determines  the  character 
of  the  restored  part  is  a  mystery.  A  worm 
is  cut  at  a  certain  point.  The  tissue  of 
one  piece  will  regenerate  head  with  all  its 
parts,  and  the  tissue  of  the  other,  at  the 
same  point,  will  regenerate  posterior  parts, 
—  unless  the  cut  be  well  forward,  when 
botJi  pieces  will  regenerate  anterior  parts, 
or  well  back,  when  both  will  regenerate  pos- 
terior parts. 

These  facts  cannot  be  explained  on  the 
theory  of  "formative  stuffs,"  because  head 
tissue  may  arise  from  posterior  positions 
and  tail  tissue  from  anterior.  For  exam- 
ple, if  an  oblique  cut  be  made  into  the 
side  of  a  planarian,  head  tissue  will  arise  if 
the  cut  be  directed  backward,  even  though 
made  well  to  the  rear,  while  tail  tissue  will 
arise  from  a  cut  directed  forward,  even 
though  made  at  a  point  so  far  ahead  that 
if  carried  entirely  across  the  body  it  would 
sever  a  piece  so  small  that  it  would  give 
rise  to  head  tissue  only  (see  Fig.  42). 

The  determining  cause  pf  these  oppo- 
site differentiations  is  yet  a  mystery. 

Lateral  regeneration.  "  Since  the  most 
familiar  cases  of  regeneration  are  those  that 
take  place  at  the  anterior  and  posterior 
ends,  we  not  unnaturally  come  to  think  of  polarity  as  a  phenom- 
enon connected  only  with  the  long  axis  of  the  animal,  but 
there  are  also  many  cases  of  lateral  regeneration  in  which  a 
similar  relation  can  be  shown." 

1  Morgan,  Regeneration,  p.  43. 


FIG.  42.  Polarity  in  re- 
generation :  regenera- 
tion from  the  two 
oblique  cuts  opening 
forward  will  produce 
"head  stuff,"  though 
one  cut  is  far  posterior ; 
on  the  other  hand,  an 
anterior  cleft  opening 
backward  produces 
tail  matter.  — After 
Morgan 


334 


CAUSES  OF  VARIATION 


If  an  incision  be  made  in  the  side  of  an  actinian,  tentacles 
will  arise  at  that  point,  and  they  will  seize  pieces  of  meat  and 
press  them  against  the  stem,  whether  a  mouth  was  formed  or 
not1  (see  Fig.  43). 

If  a  planarian  be  split  lengthwise  into  right  and  left  halves, 
regeneration  takes  place  whether  the  halves  be  equal  or  unequal. 
The  completed  worm  will  be  at  first  both  narrower  and  shorter 

than  the  normal,  but  with  time  and 
feed  it  will  equal  or  even  exceed 
the  original.  How  the  nerve  cords 
and  genital  ducts  are  formed  anew, 
especially  from  the  piece  so  far  to 
one  side  as  to  include  none  of  their 
substance,  is  a  mystery  closely  akin 
to  that  of  original  differentiation 
from  the  fertilized  ovum.  If  the 
slice  be  taken  well  to  one  side,  no 
head  matter  is  included.  In  such 
a  case  the  head  appears  first  at 
the  side  of  the  piece,  but  later  it 
assumes  its  proper  position. 

Regeneration  from   an   oblique 
surface.   If  the  tail  of  a  tadpole 
though  no  mouth  were  present.  —    be    removed   by  an   oblique    cut, 

the  regenerated  tail  will  at  first 

stand  at  right  angles  to  the  cut  and  obliquely  to  the  axis  of  the 
tail.  As  growth  proceeds,  however,  the  tail  gradually  swings 
into  line  with  the  axis  of  the  body. 

If  the  head  of  a  planarian  be  removed  by  an  oblique  cut,  it  will 
begin  to  regenerate  at  the  forward  part,  making  the  head  at  first 
stand  at  right  angles  to  the  cut,  and  not  in  line  with  the  body. 

If  a  piece  be  taken  from  the  middle  of  a  planarian  by  two 
parallel  but  oblique  cuts  (for  example,  running  backward  from 
left  to  right),  the  head  will  begin  to  regenerate  from  the  anterior 
end  at  its  forward  (left)  side,  while  the  tail  will  begin  at  the 
posterior  extremity  but  on  the  opposite  side,  the  final  result  being 
complete  restoration  of  the  normal  shape. 

1  Loeb,  Physiology  of  the  Brain,  p.  52. 


FIG.  43.  Lateral  regeneration  :  a  cut 
in  the  side  of  an  actinian  produced 
a  clump  of  tentacles  which  would 
seize  a  piece  of  meat  and  press  it 
against  the  side  of  the  body,  even 


RELATIVE  STABILITY   OF   LIVING  MATTER        335 

That  the  new  material  produced  in  regeneration  is  at  first 

totipotent  —  that  is,  capable  of  more  than  one  differentiation 

is  easily  shown.  If  a  short  piece  be  cut  from  the  middle  of  a 
planarian,  and  if,  after  the  new  material  has  begun  to  form,  the 
whole  mass  be  split  lengthwise,  both  halves  will  develop  heads 
directly;  but  if  the  split  is  not  made  "  until  just  before  the 
formation  of  a  head,  then  each  half  piece  produces  at  first  a 
half  head,  that  completes  itself  later  at  the  cut  side."  1 

Again,  if  the  head  be  cut  from  a  planarian  and  the  body  be 
split  for  a  distance,  the  split  will  heal  and  a  single  head  will 
regenerate ;  but  if  a  slice  be  taken  out  of  the  middle  line  of  the 
body,  or  if  otherwise  the  two  pieces  be  prevented  from  fusing, 
then  two  heads  will  regenerate,  one  on  each  piece.2  These  two 
heads  may  later  pull  apart  with  sufficient  force  to  tear  the  body.3 

All  these  phenomena  reveal  great  capability  of  readjustment 
as  to  more  or  less  differentiated  tissue.  The  more  the  matter  is 
studied  the  more  we  discover  that  the  line  between  regeneration 
and  development  is  one  of  degree  rather  than  of  kind,  and  that 
differentiation  in  both  cases,  whether  normal  or  abnormal,  rests 
upon  causes  very  imperfectly  understood  but  closely  akin  to 
those  of  differentiation  in  general. 

SECTION   IX  — EVIDENCE    FROM   GRAFTING 

When  tissue  of  one  kind,  plant  or  animal,  is  removed  from 
its  connections  and  set  into  tissue  of  the  same  or  of  a  different 
kind,  and  a  union  takes  place  so  that  growth  ensues,  the  union  is 
called  a  graft.  From  our  standpoint  no  little  interest  attaches  to 
the  variety  of  conditions  under  which  grafts  may  be  effected,  and 
to  the  fact  that  the  growth  upon  the  graft  is  like  the  part  set  in 
and  not  like  the  tissue  that  supports  it,  —  the  host  acts  only  as 
affording  standing  room  and  food  supply  to  the  graft.  Again,  if 
two  dissimilar  pieces  are  joined,  each  preserves  its  identity. 

Grafting  is  comparatively  easy  among  plants,  though  the  species 
that  may  be  joined  are  limited.  Among  animals  it  is  more  diffi- 
cult, but  by  no  means  impossible. 

1  Morgan,  Regeneration,  p.  49.  2  Ibid.  p.  50. 

3  Loeb,  Physiology  of  the  Brain,  p.  82. 


336  CAUSES  OF  VARIATION 

Born  succeeded  in  uniting  tadpoles  of  two  different  species  of 
frogs,  Rana  esculenta  for  the  anterior  part  and  R.  arvalis  for  the 
posterior.  This  "made-up"  animal  lived  seventeen  days.  Harrison 
succeeded  in  keeping  an  individual  made  up  of  R.  virescens  and 
R.palnstris  until  its  transformation  from  a  tadpole  into  a  frog.1 

In  the  same  way  earthworms  may  be  built  up  of  two  or  more 
individuals  of  the  same  or  of  different  species,  and  the  pieces  used 
in  this  building  up  may  even  be  reversed,  so  that  the  middle  part 
of  the  made-up  worm  may  have  its  posterior  part  placed  anteri- 
orly, or  the  reverse.  Worms  may  be  made  with  two  heads,  with 
or  without  a  tail,  or  with  two  tails,  with  or  without  a  head,  - 
though  the  latter,  for  obvious  reasons,  can  live  but  a  short  time.2 

Ribbert  grafted  a  portion  of  mammary  gland  into  the  ear  of 
the  guinea  pig,  where  it  grew,  and  when  the  pig  became  pregnant 
the  grafted  tissue  secreted  milk? 

The  whole  subject  of  grafting,  even  more  than  that  of  regen- 
eration, shows  the  wonderfully  persistent  nature  of  differentiated 
tissue,  though  it  shows  also  the  variety  of  conditions  under  which 
its  activities  may  be  discharged. 

SECTION  X  — EVIDENCE  FROM  THE  ORIGIN  OF   NEW 
CELLS  AND   TISSUES 

New  tissue  may  arise  in  regeneration  in  three  distinct  ways  : 

1 .  It  may  arise  from  tissue  of  its  own  kind  ;  that  is,  the  tissue 
produced  in  regeneration  may  arise  from  the  same  kind  of  tissue 
in  the  organism. 

2.  It  may  arise,  not  from  like  tissue,  — of  which  none  may  be 
present,  —  but  from  the  same  point  of  origin  and  in  the  same 
manner  as  during  embryonic  development. 

3.  It  may  arise  from  a  source  entirely  different  from  that  of 
embryonic  development,  and  in  this  case  may  be  either  normal 
or  heterom orphic. 

Examples  of  the  first  class  are  everywhere  at  hand  ;  indeed, 
this  is  the  most  ordinary  form  of  regeneration,  and  many  have 
erroneously  supposed  it  to  be  the  only  form.  Ordinarily,  muscle 

1  Morgan,  Regeneration,  pp.  184-185.  2  Ibid.  pp.  171-173. 

3  Loeb,  Physiology  of  the  Brain,  p.  206 


RELATIVE  STABILITY  OF   LIVING  MATTER         337 

gives  rise  to  muscle,  nerve  to  nerve,  bone  to  bone,  and  each  part- 
to  its  own  kind  by  the  simple  method  of  growth  extension. 

This,  however,  is  the  simplest  method  of  regeneration,  and 
more  complex  methods  are  necessary  in  extreme  regeneration, 
where  the  entire  supply  of  certain  tissues  is  cut  away,  and  the 
new  growth  must  arise  from  different  tissue  or  not  at  all. 

Examples  of  the  second  class  are  less  common,  but  not  rare. 
Where  an  entire  limb  is  gone  regeneration  must  proceed  upon  a 
plan  different  from  the  one  it  would  follow  were  only  a  single 
tissue  involved,  like  a  wounded  muscle.  The  first  new  growth 
that  arises  must  in  some  way  be  endowed  with  the  power  of  pro- 
ducing not  one,  but  many,  different  kinds  of  tissues.  Gotte,  as 
quoted  by  Morgan,  has  studied  both  « the  embryonic  development 
and  the  regeneration  of  the  limb  of  triton,  especially  in  regard  to 
the  origin  of  the  new  bones.  He  found  that  the  skeleton  develops 
in  much  the  same  way  in  the  embryonic  limb  and  in  the  regener- 
ating limb,  and  the  process  in  the  latter  may  be  said  to  repeat  that 
in  the  former."  If  the  larva  is  young,  the  new  growth  differs  but 
little  from  the  old,  but  if  the  bones  had  become  ossified,  the 
difference  between  the  two  is  much  more  marked.1  Curiously 
enough  the  salamander  regenerates  the  tail  completely,  bones 
and  all,  but  the  regenerated  tail  of  a  lizard  contains  not  a  new 
series  of  bones,  but  a  cartilaginous  tube  which  is  attached  to  the 
broken  seventh  caudal  vertebra.2 

An  example  of  the  third  case,  in  which  tissue  is  regenerated 
from  a  source  different  from  that  of  embryonic  development,  is 
shown  in  the  reproduction  of  the  lens  of  the  eye  of  the  salamander 
or  of  triton.  In  this  case,  if  the  lens  be  removed  a  new  one  is  re- 
generated from  the  upper  edge  of  the  iris,  a  part  of  the  body  from 
which  the  lens  of  the  eye  never  develops  normally  in  the  em- 
bryo of  this  or  of  any  other  vertebrate.  In  the  embryo  the  lens 
develops  from  the  ectoderm  at  the  side  of  the  head,  having  no 
connection  with  the  iris. 

The  regeneration  from  like  tissue  is  no  more  difficult  of  com- 
prehension than  is  ordinary  growth,  and  that  which  repeats  the 

1  Morgan,  Regeneration,  pp.  200-201. 

2  Ibid.  p.  198.    The  lizard's  tail  does  not  break  between  the  two  vertebras,  which 
are  strongly  joined,  but  in  the  middle  of  the  vertebra,  which  is  relatively  weak. 


338  CAUSES  OF  VARIATION 

course  of  embryonic  development  is  involved  in  the  mystery  of 
ordinary  differentiation  from  totipotent  or  indifferent  tissue  ;  but 
regenerated  matter  which  arises  from  tissue  in  no  wise  involved 
in  embryonic  development  would  seem  to  be  outside  of  the  influ- 
ence of  heredity.  In  the  latter  case  it  may  result  in  normal  tis- 
sue, as  in  the  lens  of  the  eye,  or  in  heteromorphic  growth,  as  in 
the  production  of  an  antenna  instead  of  an  eye,  or  of  a  foot  instead 
of  an  antenna. 

SECTION   XI  — EVIDENCE    FROM    DEVELOPMENT   AND 
DIFFERENTIATION  J 

From  the  fertilized  ovum  to  the  fully  differentiated  adult  in- 
dividual of  the  highest  species  is  a  long  step.  Nothing  is  more 
evident  than  that  all  this  differentiation  is  the  result  of  forces 
resident  within  the  single  cell  of  the  oviim.  Whatever  office  is 
discharged  by  outside  agencies,  and  whatever  deviations  or  modi- 
fications are  produced  thereby,  the  impulse  to  differentiate  and 
the  direction  of  differentiation  arise  from  forces  internal  to  the 
organism.  Moreover,  this  differentiation,  great  as  it  is  in  the 
finished  product,  when  traced  backward  merges  by  imperceptible 
shades  each  into  the  next  preceding,  until  the  undifferentiated 
ovum  is  reached  at  the  end  (or  beginning)  of  the  series. 

What  is  the  nature  of  these  internal  forces,  and  what  are  the 
agencies  that  set  them  in  motion,  are  the  chief  mysteries  in  ani- 
mal and  plant  development.  That  a  single  germ  cell,  similar  in 
its  essential  nature  to  any  one  of  the  tissue  cells  of  which  the 
body  is  composed,  —  that  such  a  cell  "  can  carry  with  it  the  sum 
total  of  the  heritage  of  the  species,  that  it  can  in  the  course  of 
a  few  days  or  weeks  give  rise  to  a  mollusk  or  a  man,  is  the 
greatest  marvel  of  biological  science."2 

"  In  attempting  to  analyze  the  problems  that  it  involves,"  con- 
tinues Wilson,  "  we  must  from  the  outset  hold  fast  to  the  fact 
on  which  Huxley  insisted,  that  the  wonderful  formative  energy  of 
the  germ  is  not  impressed  upon  it  from  without,  but  is  inherent 
in  the  egg  as  a  heritage  from  the  parental  life  of  which  it  was 
originally  a  part.  The  development  of  the  embryo  is  nothing  new. 

1  Wilson,  The  Cell,  p.  430.  2  Ibid.  p.  396. 


RELATIVE  STABILITY  OF   LIVING  MATTER         339 

It  involves  no  breach  of  continuity,  and  is  but  a  continuation  of 
the  vital  processes  going  on  in  the  parental  body.  What  gives 
development  its  marvelous  character  is  the  rapidity  with  which 
it  proceeds,  and  the  diversity  of  the  results  attained  in  a  span 
so  brief." 

We  can  define  the  chief  mystery  of  development  as  lying  in 
the  facts  of  differentiation  and  definite  termination  to  growth,  but 
if  we  ask  how  the  impulses  governing  such  complicated  results  lie 
latent  in  a  single  cell,  and  how  they  operate  in  orderly  sequence 
beginning  and  ending  at  the  proper  moment,  we  have  asked  the 
"  final  question,"  and  "  in  approaching  it,"  says  Wilson,  "  we  may 
as  well  make  a  frank  confession  of  ignorance." 

About  all  we  can  hope  to  do  in  the  present  state  of  knowledge 
is  to  throw  light  upon  the  question  of  comparative  stability  of 
organized  matter  and  note  the  conditions  under  which  one  kind 
of  cell  gives  rise  to  another  of  a  different  order.  On  this  point 
certain  facts  of  development  have  an  important  bearing. 

Cell  division.  All  differentiation  during  development  is  by 
cleavage  of  the  germ  cell.  The  phenomena  of  division  and  mito- 
sis are  in  general  the  same  in  the  cleavage  of  the  germ  cell  and 
the  development  of  the  embryo  as  in  the  division  of  ordinary 
tissue  cells,  except  that  the  body  cells  for  the  most  part  give 
rise  only  to  others  like  themselves,  while  those  of  the  germ  and 
the  embryo  give  rise  not  only  to  others  like  themselves  but  to 
many  different  kinds  as  well. 

This  distinction  is  relative  rather  than  absolute,  for  we  remem- 
ber that  in  certain  species  a  small  part,  even  a  leaf,  is  able  by 
regeneration  to  give  rise  to  a  new  individual,  involving  differen- 
tiation similar  if  not  equal  to  that  of  embryonic  development. 
However,  in  many  species  and  with  most  tissues  the  power  of 
typical  differentiation  appears  to  be  lost  in  the  first  development. 
In  this  connection  it  is  well  to  remind  ourselves  that  in  many 
species  the  amount  of  chromatin  matter  in  the  somatic  cells  is 
different  from  that  in  the  germ  cells.1 

Geometrical  character  of  cleavage.  The  earliest  cleavage  of 
the  germ  cell  is  governed  by  two  definite  geometric  principles 
announced  by  Sachs  :  (i)  the  cell  typically  tends  to  divide  into 

1  Wilson,  The  Cell,  p.  426  (concerning  Boveri's  investigations  on  Ascaris). 


340  CAUSES  OF  VARIATION 

equal  parts ;  (2)  each  new  plane  of  division  tends  to  intersect 
the  preceding  one  at  a  right  angle.1 

A  typical  cleavage  of  a  spherical  egg  would  be,  first,  vertical, 
dividing  into  right  and  left  halves  ;  second,  also  vertical,  but  at 
right  angles  to  the  first,  dividing  into  dorsal  and  ventral  portions ; 
third,  horizontal,  dividing  into  anterior  and  posterior  parts ;  — 
after  which  all  sorts  of  irregularities  might  be  expected,  including 
cleavages  parallel  with  the  surface,  cutting  in  two  the  long  cells 
that  formerly  extended  to  the  center.  The  egg  of  the  holothu- 
rian,  like  those  of  Synapta,  proceeds  regularly  until  as  many  as 
512  cells  are  reached,2  while  others  become  irregular  almost  at 
once,  some  quadrants  dividing  much  more  rapidly  than  others. 

Variation  in  the  rate  of  division.  If  division  proceeds  with 
perfect  regularity,  the  number  of  cells  will  of  course  form  an 
increasing  geometrical  series  whose  ratio  is  two,  —  2,  4,  8,  16, 
32,  64,  128,  256,  512,  1024,  etc.  Such  a  series  has  been  men- 
.tioned,  extending  to  512. 

This  uniform  series  is  rarely  realized,  however,  owing  to  irreg- 
ularities in  the  rate  of  division ;  for  example,  Nereis  regularly 
gives  rise  to  the  series  2,  4,  8,  16,  20,  23,  29,  32,  37,  38,  41,  42, 
"  after  which  the  order  is  more  or  less  variable."  3 

In  some  portions  of  the  dividing  cell  the  cleavage  proceeds 
therefore  with  much  greater  rapidity  than  in  others,  nor  is  the  plan 
uniform  in  all  cases,  though  the  results  achieved  may  be  sub- 
stantially identical.  In  general  the  rate  of  division  is  most  rapid 
in  the  upper  hemisphere  of  the  ovum,  and  in  some  instances  it  pro- 
ceeds very  slowly,  with  long  pauses,  in  the  lower,  giving  great 
irregularity  in  the  size  of  cells. 

Temporary  effect  of  outside  influences  upon  cleavage.  Driesch 
placed  eggs  of  sea  urchins  under  pressure  sufficient  to  flatten  the 
spheres  to  disks.  In  this  position  "the  amphiasters  all  assume 
the  position  of  least  resistance,  i.e.  parallel  to  the  flattened  sides, 
and  the  egg  segments  as  a  flat  plate  of  eight,  sixteen,  or  thirty- 
two  cells.  This  is  totally  different  from  the  normal  form  of 
cleavage  ;  yet  such  eggs  when  released  from  pressure  are  capable 
of  development  and  give  rise  to  normal  embryos."  4  Without 

1  Wilson,  The  Cell,  p.  362.  »  Ibid.  p.  366. 

2  Ibid.  p.  364.  4  Ibid.  p.  375.    Italics  are  mine. 


RELATIVE  STABILITY  OF  LIVING  MATTER 


341 


doubt  in  nature  similar  temporary  effects  are  caused  by  internal 
stress  or  pressure  of  the  parts  of  the  egg  itself. 

After  noting  other  causes  of  irregularity,  Wilson  fittingly 
observes  : 

All  these  considerations  drive  us  to  the  view  that  the  simpler  mechanical 
factors,  such  as  pressure,  form,  and  the  like,  are  subordinate  to  far  more 
subtle  and  complex  operations  involved  in  the  general  development  of  the 
organism.  .  .  .  We  cannot  comprehend  the  forms  of  cleavage  without  refer- 
ence to  the  end  results}- 

Promorphology  of  the  ovum.  Is  there  something  in  the  origi- 
nal shape  or  character  of  the  egg  that  corresponds  to  the  fin- 
ished individual  ?  Is  there  a  polarity  of  the  egg  that  is  in  any 
way  related  to  the  order  of  cleavage  and  the  axis  of  the  body  ? 

Speaking  of  the  eggs  of  insects,  Wilson  says  : 2 

In  a  large  number  of  cases  the  egg  is  elongated  and  bilaterally  sym- 
metrical, and,  according  to  Blochmann  and  Wheeler,  may  even  show  a 
bilateral  distribution  of  the  yolk  corresponding  with  the  bilaterality  of 
the  ovum. 

Hallez  is  here  quoted  as  asserting,  after  a  study  of  the  cock- 
roach, water  beetle,  and  the  locust,  that  "  the  egg  cell  possesses 
the  same  orientation  as  the  maternal  organism  that  produces  it ; 
it  has  a  cephalic  pole  and  a  caudal  pole  ;  a  right  side  and  a  left ; 
a  dorsal  aspect  and  a  ventral ;  and  these  different  aspects  of  the 
egg  coincide  with  the  corresponding  aspects  of  the  embryo." 
Wheeler,  after  studying  some  thirty  different  species  of  insects, 
reached  the  same  result,  and  concluded  that  even  when  the  egg 
approaches  the  spherical  form-  the  symmetry  still  exists,  though 
obscured.3 

In  species  other  than  insects  the  egg  often  has  a  bilateral 
symmetry  of  its  own,  "sometimes  so  clearly  marked  that  the 
exact  position  of  the  embryo  may  be  predicted  in  the  unferti- 
lized egg."3 

Polarity  of  the  ovum.  It  is  now  well  known  that  in  the  seg- 
menting eggs  of  the  frog  the  first  two  cleavage  planes  are  vertical, 
the  first  corresponding  to  the  median  plane  of  the  body  and  set- 
ting off  right  and  left  halves  (which  develop  into  corresponding 

i  Wilson,  The  Cell,  pp.  376-377.  2  Ibid.  pp.  383-384-  3  Ibid-  P;  384- 


342  CAUSES  OF   VARIATION 

parts  of  the  body),  the  second  setting  off  dorsal  and  ventral 
areas ;  while  the  third, which  is  horizontal,  divides  into  anterior 
and  posterior  portions. 

The  process  is  the  same  in  many  species,  and  "  wherever  the 
egg  axis  can  be  determined  by  the  accumulation  of  the  deuto- 
plasm  in  the  lower  hemisphere  the  egg  nucleus  sooner  or  later  lies 
eccentrically  in  the  upper  hemisphere,  and  the  polar  bodies  are 
formed  at  the  upper  pole." 

In  such  cases  of  distinct  polarity  the  cleavage  planes  are  prac- 
tically predetermined,  and  the  products  of  division  have  each 
their  definite  r61e  in  development.  Thus  the  upper  hemisphere 
(so-called  animal  pole)  is  the  seat  of  most  active  division,  with 
smaller  cells,  which  develop  into  cerebral,  dorsal,  and  anterior 
portions  of  the  body ;  while  the  lower  hemisphere  (vegetable  or 
nutritive  pole)  divides  more  slowly,  its  cells  are  larger,  and  they 
develop  into  the  alimentary  organs  and  the  posterior  and  ventral 
parts  generally.1 

While  this  rule  is  not  absolute  in  all  species,  it  yet  indicates  a 
broad  general  principle  that  lies  at  the  very  threshold  of  devel- 
opment ;  namely,  that  the  original  impulse  to  direction  of  growth 
lies  in  the  polarity  of  the  ovum. 

Cause  of  polarity  in  the  ovum.  Gravity  would  seem  to  be  the 
controlling  cause  in  establishing  a  kind  of  polarity  in  the  ovum. 
The  nucleus  being  of  low  specific  gravity,  tends  to  lie  eccentrically 
nearer  the  upper  side  of  the  ovum,  and  the  heavier  deutoplasm 
settles  to  the  lower  side,  the  parts  arranging  themselves  accord- 
ing to  relative  weight,  like  starch  granules  or  other  cell  contents. 
Moreover,  Born  has  shown  that  "  if  frogs'  eggs  be  fastened  in 
an  abnormal  position,  —  e.g.  upside  down  or  on  the  side, — 
rearrangement  of  the  egg  material  takes  place  "  and  "  a  new  axis 
is  established  in  the  egg."2  Schultze  discovered  that  ".if  the  egg 
be  turned  upside  down  when  in  the  two-celled  stage  a  whole 
embryo  (or  half  of  a  double  embryo)  may  arise  from  each  blasto- 
mere,  instead  of  a  half  embryo  as  in  the  normal  development, 
and  that  the  axes  of  these  embryos  show  no  constant  relation 
to  one  another."  2  Morgan  learned  that  "  either  a  half  embryo 

1  Wilson,  The  Cell,  pp.  378,  379. 

2  Ibid.  p.  422. 


RELATIVE   STABILITY  OF  LIVING   MATTER 


343 


or  a  whole  half-sized  dwarf  might  be  formed,  according  to  the 
position  of  the  blastomere."  l 

Causes  of  differentiation.    These  facts  show  : 

1.  That  a  primary  cause  of  differentiation  lies  in  the  polarity 
of  the  ovum. 

2.  That  this  polarity  is  due  primarily  to  gravity  separating 
its  heavier  from  its  lighter  parts. 

3.  That  the  egg  is  at  first,  in  many  cases  at  least,  indifferent, 
and  that  its  polarity  may  even  be  changed  after  having  once 
been  well  established. 

4.  That  if  the  segmenting  ovum  may  be  separated  into  its 
blastomeres,  and  each  may  produce  a  complete  individual  (Am- 
phioxus,  etc.),2  then  the  egg  as  a  whole  is  not  only  totipotent 
but  its  earlier  segments  as  well  are  each  capable  of  producing 
all  the  parts  of  the  body. 

5 .  The  polarity  and  the  development  of  a  part  are  influenced 
largely  by  its  position  with  reference  to  other  and  especially 
larger  parts. 

Roux  found  that  when,  in  the  two-celled  stage  of  the  frog's  egg, 
one  of  the  blastomeres  was  killed  by  a  hot  needle,  the  remaining 
one  developed  a  half  embryo,3  whereas  in  many  cases  a  single 
blastomere  is  known  to  be  entirely  capable  of  producing  a  whole 
embryo  if  freed  from  its  neighbors. 

Again,  a  section  from  an  earthworm  tends  to  regenerate 
head  matter  at  its  anterior  end  and  tail  matter  at  its  posterior 
end ;  but  if  a  small  piece  be  grafted,  even  in  a  reversed  position, 
on  the  anterior  end  of  a  larger  piece,  it  will  regenerate  head 
matter  from  its  posterior  extremity,  showing  how  the  polarity  of 
the  smaller  piece  is,  so  to  speak,  overcome  by  that  of  the  larger.4 

A  consideration  of  these  facts  leads  Wilson  to  quote  Hertwig 
as  follows  :  The  relative  position  of  a  blastomere  in  the  whole 
{assemblage'}  determines  in  general  what  develops  from  it;  if  its 
position  be  changed,  it  gives  rise  to  something  different ;  in  other 
words,  its  prospective  value  is  a  function  of  its  position?* 

1  The  different  cells  of  the  earlier  cleavages  (the  2-,  4-,  8-,  i6-celled  stages,  etc.) 
are  known  as  blastomeres. 

"~  Wilson,  The  Cell,  p.  423.  4  Morgan,  Regeneration,  p.  8. 

3  Ibid.  p.  380.  5  Wilson,  The  Cell,  p.  41 5- 


344 


CAUSES  OF  VARIATION 


6.  Whether  the  above  statement  is  absolutely  or  only  rela- 
tively true,  the  fact  is  clear  that  living  matter  will  often  go 
through  its  changes   and   complete   its   cycle   of   development 
under  extreme  hardship.    For  example,  in  some  species  a  blas- 
tomere  from  the  two-  or  from  the  four-celled  stage  may  develop 
into  a  whole  (dwarf)  embryo  or  into  a  half  embryo,  while  in 
others  (ctenophore)  each  one  of  the  first  eight  may  develop  into 
a  symmetrical  and  therefore  complete  individual,  but  lacking  the 
full  normal  number  of  swimming  plates} 

7.  The  conclusion  is  unavoidable  that  living  matter  is  endowed 
with  wonderful  elasticity  and  persistence  of  plan,  or  an  approxi- 
mation to  it,  even  under  most  adverse  conditions,  providing  only 
these  conditions  do  not  destroy  life. 

And  so  we  return  to  the  original  questions  :  How  much  of 
what  the  individual  is  to  be  is  due  to  inheritance  ?  How  flex- 
ible is  the  plan  ?  To  what  extent  are  modifications  possible,  and 
to  what  extent  are  variations  inherited  ? 

Summary.  In  general  the  facts  of  differentiation  and  of  regen- 
eration, together  with  the  persistence  of  an  established  type  in 
carrying  forward  inherited  qualities  even  under  most  adverse 
conditions,  indicate  extreme  stability  of  living  matter. 

On  the  other  hand,  the  facts  of  acclimatization  argue  for  the 
alterability  of  protoplasm,  both  as  to  constitution  and  as  to  func- 
tion, inclining  one  strongly  to  the  belief  that  such  alteration  may 
become  more  or  less  permanent  with  the  organism. 

Altogether  the  conviction  is  forced  upon  us  that  the  activities 
of  living  matter  proceed  upon  a  plan  inspired  from  within  and 
arising  from  the  nature  of  the  organization,  but  that  this  plan 
has  accommodated  itself  to  surrounding  conditions  in  the  past 
and  is  entirely  competent  to  do  so  again  whenever  sufficient 
occasion  arises,  provided  only  that  the  new  demands  be  not  too 
sweeping  or  too  suddenly  imposed. 

These  facts  need  to  be  constantly  in  the  mind  of  the  farmer, 
who  must  be  prepared  for  comparatively  sweeping  changes  from 
apparently  slight  causes. 

We  pass  now  to  a  discussion  of  the  question  as  to  whether  or 
not  individual  modifications  may  be  transmitted. 

1  Wilson,  The  Cell,  p.  418. 


RELATIVE  STABILITY  OF  LIVING  MATTER 


ADDITIONAL  REFERENCES 


345 


A  NATURAL  HYBRID.    Experiment  Station  Record,  XV,  677. 

EFFECT  OF  STOCK  UPON  SCION.    Experiment  Station  Record,  XV,  363. 

EXPERIMENTAL  ZOOLOGY.    By  T.  H.  Morgan.    Chapters  XV-XXII,  pp. 

239-346. 
GRAFTING  BEETS.  (Colors  that  do  not  blend.)   Experiment  Station  Record, 

XIV,  353. 
GRAFTING  EXPERIMENTS  WITH  TADPOLES.    By  R.  G.  Harrison.    Science, 

VII,  198-199. 
INFLUENCE  OF  STOCK  UPON  SCION.    By  T.  J.  Burrill,  Transactions  of  the 

Illinois  Horticultural  Society,  1898,  pp.  62-72.    Experiment  Station 

Record,  XI,  51,  152,  250. 
INFLUENCE  OF  STOCK  UPON  SCION.    Experiment  Station  Record,  VII, 

309- 
MODIFICATIONS  IN  PARASITIZED  CELLS.    Experiment  Station  Record, 

XIV,  121. 

REGENERATION  OF  BEGONIA.    Experiment  Station  Record,  XIV,  528. 
RESEMBLANCE   BETWEEN   CELLS    OF   MALIGNANT  GROWTHS   IN   MAN 

AND  NORMAL  REPRODUCTIVE  TISSUE.    Proceedings  of  the  Royal 

Society,  LXXII,  499-504. 
VARIABILITY  OF  ORGANISMS  AND  OF  THEIR  ELEMENTS.    Science,  XV, 

1-5- 


PART    III  —  TRANSMISSION 


Up  to  this  point  the  study  has  been  confined  to  the  nature 
and  kinds  of  variations  that  may  arise,  together  with  the  causes 
that  lead  to  their  appearance.  We  come  now  to  inquire  whether, 
and  to  what  extent,  these  variations  are  transmissible. 

This  is  the  all-important  question,  because  variations  that 
are  not  transmitted  are  manifestly  of  no  consequence  except 
to  the  individual.  Whether  desirable  or  undesirable,  they  have 
no  opportunity  to  affect  the  race  as  a  whole  either  favorably 
or  unfavorably.  We  may  therefore  disregard,  in  all  questions  of 
race  improvement,  any  and  all  deviations  that  are  not  trans- 
missible. 

Those  that  are  transmitted,  however,  are  by  that  fact  destined 
to  exert  a  more  or  less  permanent  influence  for  good  or  evil. 
Accordingly  we  cannot  know  too  much  about  this  class  of  vari- 
ations and  the  circumstances  under  which  they  descend  from 
generation  to  generation  and  ultimately  come  to  characterize,  if 
not  to  dominate,  the  type  of  the  race. 

The  student,  and  the  breeder  as  well,  is  likely  to  become  con- 
fused by  the  ceaseless  panorama  of  characters  and  variations 
presented  to  his  view  as  generations  come  and  go,  involving 
sometimes  literally  multitudes  of  individuals  of  all  shades  of 
difference.  He  must  learn  to  pass  this  procession  before  his 
mental  vision  with  the  full  realization  that  a  large  portion  of  all 
that  he  sees  will  have  no  permanent  influence  upon  the  race. 
He  must  become  acute  in  detecting  the  significant  factors,  which 
are  those  only  that  are  connected  with  transmission. 

The  study  of  race  improvement  is,  therefore,  essentially  a 
study  of  the  laws  that  govern  transmission, — all  that  has  gone 
before  being  preparatory  to  that  study.  Upon  two  questions 
the  breeder  must  fix  his  attention,  —  What  is  transmitted,  and 
how  is  tJie  transmission  accomplished  / 

347 


CHAPTER  XI 

TRANSMISSION  OF  MODIFICATIONS  DUE  TO  EXTERNAL 
INFLUENCES 

SECTION  I  —  INTRODUCTORY 

In  the  discussion  of  the  causes  of  variation  a  clear  distinction 
was  made  between  causes  internal  and  causes  external  to  the 
organism.  This  distinction  should  still  be  borne  in  mind,  though 
the  principal  discussion  and  all  of  the  controversy  arise  in  con- 
nection with  external  causes. 

Variations  due  to  causes  internal  to  the  germ  are  transmitted. 
So  far  as  the  writer  is  aware,  no  one  has  ever  disputed,  or  even 
questioned,  the  correctness  of  this  proposition.  It  is  fundamental, 
if  not  axiomatic,  that  any  change  taking  place  in  the  structure 
of  the  germinal  matter,  which  is  passed  on  from  generation 
to  generation,  which  is  the  bearer  of  all  characters  and  the 
exclusive  basis  of  all  transmission,  —  that  any  such  alteration 
will  of  necessity  make  itself  manifest  at  once,  and  indefinitely 
afterward  ;  indeed,  as  long  as  the  change  in  the  constitution  of 
the  germ  continues.  This  is  the  purpose  of  all  selective  mating, 
—  to  secure  a  germ  endowed  with  as  many  as  possible  of  what 
are  considered  to  be  desirable  variations,  tending  to  maximum 
development,  and  as  few  as  possible  that  are  undesirable,  and 
these  with  a  minimum  development.  Such  a  germ  should 
develop  an  embryo,  and  finally  an  adult  individual,  with  the 
highest  obtainable  degree  of  excellence. 

To  control  the  germ  is  the  purpose  of  all  selection.  'It  is  the 
object  of  all  breeding.  We  practice  line  breeding,  and  even 
in-breeding,  to  give  intensity  along  certain  lines ;  we  resort  to 
mixed  breeding,  even  to  cross  breeding,  to  introduce  new  vari- 
ations and  to  endow  the  race  with  greater  flexibility. 

It  is  in  the  germ  that  mutations  arise.  The  causes  are 
obscure,  but  it  is  here,  in  the  constitution  of  the  germinal 

348 


TRANSMISSION   OF   MODIFICATIONS  349 

matter,  that  they  are  at  work,  and  it  is  here  that  races  are 
enriched,  almost  miraculously,  with  new  and  valuable  endow- 
ments, —  not  frequently  and  freely,  but  occasionally  and  spar- 
ingly. These  are  the  free  gift  of  nature,  arising,  so  far  as  we 
can  now  see,  spontaneously,  but  due,  as  we  firmly  believe,  to 
definite  influences  at  work  within  the  germ,  which  is  the  avenue 
of  all  transmissible  variations. 

Remembering,  then,  that  all  influences  that  affect  the  germ 
will  give  rise  to  variations,  we  come  now  to  the  direct  question 
of  the  chapter,  —  Are  the  modifying  effects  of  external  influences 
transmitted  ?  or  does  each  generation  begin  anew,  unhampered 
and  unhelped  by  the  direct  effects  of  previous  environment, 
whether  favorable  or  unfavorable  ? 

The  main  question.  This  is  an  exceedingly  important  matter  ; 
indeed,  no  other  question  in  all  evolution  is  of  such  immediate 
and  far-reaching  consequence  in  thremmatology.  This  is  because 
the  influences  of  environment  are  insidious  and  at  the  same 
time  well-nigh  irresistible.  If  their  effects  are  also  transmis- 
sible, they  will  become,  like  compound  interest  or  any  other 
geometrical  progression,  strongly  and  rapidly  cumulative,  and 
therefore  tremendously  powerful  either  for  good  or  for  evil. 

This  is  the  old  and  hotly  contested  question  of  "  inheritance 
of  acquired  characters,"  better  stated  for  our  purposes  in  the 
form,  Are  the  effects  of  environment  transmitted  ?  It  is  but 
fair  to  warn  the  student  that  this  is  at  once  the  most  difficult 
and  the  most  complicated  of  all  the  questions  of  evolution,  and 
that  not  only  must  its  study  be  critically  conducted  but  the 
student  must  be  constantly  mindful  of  certain  fundamental 
considerations,  a  few  of  which  it  will  be  well  to  note  before 
proceeding  to  the  discussion  of  the  main  question. 

What  is  a  deviation?  What  we  call  a  variation,  a  devia- 
tion, or  a  modification,  is  not,  like  a  character,  an  entity  that 
can  be  transmitted.  It  is  rather  the  degree  to  which  a  character 
attains,  as  measured  from  the  general  mean  or  average  of  the 
race  as  a  whole.  When  we  speak,  therefore,  of  the  trans- 
mission of  a  variation  or  a  modification,  we  mean  literally  the 
transmission  of  the  character  as  modified,  either  by  internal  or 
external  causes. 


350  TRANSMISSION 

Strictly  speaking,  therefore,  it  is  the  character,  and  not  its 
modification,  which  is  transmitted,  and  what  we  desire  to  know, 
is,  whether  the  modification  of  a  character  in  a  particular  indi- 
vidual tends  to  become  permanent ;  that  is  to  say,  whether  a 
character  that  has  undergone  modification  will  be  transmitted  in 
its  modified  or  in  its  unmodified  form. 

In  this  connection  the  student  must  be  reminded  that  we 
have  no  way  of  judging  what  characters  or  what  modifications 
are  born  into  an  individual  except  by  the  development  they 
attain  in  his  own  personality  after  reaching  the  adult  stage.1 

For  example,  when  noting  an  average  individual  we  cannot  say 
whether  he  is  one  that  was  exceptionally  well  born,  with  fair 
opportunities  for  development ;  whether  he  was  only  fairly  well 
born,  but  with  exceptional  opportunities ;  or  whether  he  is  an 
average  both  as  to  birth  and  opportunity.  All  three  combina- 
tions would  produce  about  an  average  individual. 

On  the  contrary,  if  he  be  an  exceptional  individual,  we  are 
fairly  safe  in  assuming  that  he  was  both  well  born  and  well  con- 
ditioned ;  but  if  he  be  one  of  the  lowest  individuals,  that  he  was 
badly  born  and  has  lived  under  hard  conditions,  —  both  of  which, 
operating  together,  make  even  an  average  development  impossible. 

Of  a  mature  individual  we  may  say,  first,  that  all  the  evident 
characters  of  which  he  stands  possessed  were  born  into  him, 
but  that  the  development  they  have  attained  is  partly  a  matter 
of  birth  and  partly  a  matter  of  the  external  conditions  of  life. 
His  difference  in  development  as  compared  with  the  mean  of  the 
race  taken  at  the  adult  stage  is  his  deviation  or  variation  (for 
we  use  the  terms  interchangeably),  and  the  question  we  are  now 
asking  is,  Are  these  individual  deviations  transmitted,  or  are  all 
characters  transmitted  according  to  a  dead  level  of  inheritance, 
leaving  all  deviations  to  be  accounted  for  as  matters  of  individual 
attainment  through  more  or  less  successful  development  ? 

Adaptations.  The  modifying  effect  of  the  conditions  of  life 
is  so  profound  that  in  nature  everywhere  both  animals  and 
plants  harmonize  with  their  environment  almost  perfectly,  thus 

1  When  the  individual  becomes  a  breeder  his  inherited  qualities  will  be  fairly 
well  indicated  by  his  powers  of  transmission.  In  this  way  an  animal  truly  may 
"  breed  better  than  he  is  himself." 


TRANSMISSION   OF   MODIFICATIONS 


351 


giving  the  appearance  of  having  been  specially  created  for  their 
particular  surroundings.  We  know  enough  of  the  causes  of 
variation,  however,  to  realize  that  this  "  fit  "  between  the  animal 
or  the  plant  and  its  environment  has  been  brought  about  by  the 
direct  action  of  outside  conditions  upon  organisms  somewhat 
plastic  and  capable  of  becoming  adapted  to  a  wide  range  of 
circumstances,  —  all  individuals  not  possessing  this  adaptability 
having  long  since  disappeared  by  natural  selection. 

Nothing  is  more  simple  and  natural  than  to  assume  that 
when  the  individual  has  acquired  some  modification  through 
the  influence  of  the  environment  it  will  transmit  this  modifica- 
tion to  its  descendants,  and  that  what  was  at  first  impressed 
from  without  gradually  becomes  hereditary,  exhibiting  all  the 
cumulative  effect  of  transmissible  qualities.  All  appearances 
are  in  favor  of  such  an  assumption,  and  it  is  the  simplest  and 
most  direct  explanation  of  the  phenomena  of  adaptation  and  of 
the  well-known  harmony  that  always  exists  between  a  species 
and  its  environment. 

But  there  are  at  least  two  other  methods  by  which  the  envi- 
ronment impresses  itself  strongly  upon  the  species,  —  both  of 
which  are  always  at  work,  both  of  which  achieve  large  results 
of  an  exactly  similar  character  and  appearance,  and  which  must 
therefore  be  either  subtracted  or  fully  accounted  for  before  we 
are  warranted  in  assuming  results  due  to  direct  transmission. 

The  first  of  these  is  the  direct  effect  of  the  conditions  of  life 
acting  separately  upon  all  the  individuals  of  each  generation 
and  all  in  the  same  direction.  This  has  all  the  appearance  of 
transmission,  but  it  is  not  cumulative,  and  can  bring  about  no 
better  adaptation  in  the  species,  and  no  greater  total  change, 
than  can  be  wrought  for  each  individual  during  its  lifetime. 
The  other  is  due  to  the  selective  effect  of  the  environment, 
which  is  cumulative,  and,  so  far  as  we  can  see,  abundantly  able 
to  account  for  all  the  phenomena  of  adaptation  and  for  the  full 
effects  of  environment. 

The  environment  always  selective.  Some  individuals  of  every 
generation  fail  utterly  to  endure  the  conditions  of  life  and,  thus 
failing,  they  leave  no  descendants.  The  next  generation,  there- 
fore, being  descended  from  the  more  adaptable  individuals,  is 


352 


TRANSMISSION 


more  nearly  in  harmony  with  the  environment,  and  this  cumu- 
lative influence,  constantly  exerted,  generation  after  genera- 
tion, slowly  but  surely  modifies  the  race  in  the  direction  of  the 
environment,  giving  again  the  appearance  of  inherited  modifica- 
tions. Now  in  nature  this  selective  influence  is  always  at  work, 
sometimes  by  actually  destroying  the  less  adaptive  individuals, 
more  often  by  affecting  not  life,  but  fertility  or  longevity,  or 
both,  through  little-noticed  but  insidious  agencies. 

This  is,  moreover,  the  most  powerful  of  all  the  means  by 
which  environment  influences  species.  It  entirely  outstrips  the 
results  of  direct  influences  upon  individuals,  and  is  fully  able 
to  account  for  all  ordinary  cases  of  environmental  influence.1 

The  source  of  the  difficulty.  Here  is  an  ever-present,  all- 
powerful  influence,  bending  species  into  harmony  with  their  en- 
vironment, and  its  effects  must  be  fully  eliminated  or  accounted 
for  before  we  can  determine  whether  a  residue  remains  to  be 
attributed  to  direct  transmission.  This  is  the  source  of  the 
greatest  difficulty  in  attempting  to  learn  whether  modifications 
are  directly  transmitted. 

This  selective  process  of  the  environment  results  in  the  indi- 
rect transmission  of  such  modifications  as  increase  the  chances 
of  the  individual  in  the  struggle  for  existence;  but  what  farmers 
want  to  know  is  whether  modifications  produced  by  the  con- 
ditions of  life  are  directly  transmitted  as  such,  —  independently 
of  the  question  whether  they  increase  or  decrease  the  chances 
of  life  in  the  individual,  and  independently  of  all  questions  of 
selection. 


1  The  individual  and  the  type.  The  student  must  be  clear  as  to  what  consti- 
tutes type.  Every  individual  must  be  considered  with  reference  to  at  least  two 
generations,  the  one  to  which  it  belongs  and  the  next.  The  type  of  a  race  at  any 
particular  moment  is  fixed  by  the  personal  qualities  of  «//its  adult  members,  and 
for  this  purpose  all  individuals  are  of  equal  weight,  and  one  character  or  differ- 
ence is  as  good  as  another.  Everything  counts  in  fixing  the  type  of  an  existing 
generation. 

But  when  the  next  generation  is  considered,  it  is  not  so.  Only  those  individuals 
count  which  succeed  in  reproducing,  and  only  those  differences  count  that  are 
transmissible.  The  initial  or  natural  type,  therefore,  as  secured  by  transmission, 
is  somewhat  different  in  succeeding  generations,  nor  is  it  ever  fully  expressed  in 
adult  members.  The  existing  and  visible  type  of  any  race  is,  therefore,  at  best 
but  an  incomplete  expression  of  its  possibilities. 


TRANSMISSION   OF  MODIFICATIONS 


353 


In  nature,  where  selection  is  unlimited,  it  does  not  greatly 
matter  whether  modifications  thus  induced  are  directly  or  indi- 
rectly transmitted,  —  the  only  difference  is  a  slight  one  in  the 
amount  of  time  required;  but  among  domesticated  species,  where 
selection  is  largely  controlled,  where  it  is  to  be  employed  for  as 
few  purposes  as  possible,  and  where  at  most,  for  economic  rea- 
sons, its  use  must  be  sparing  as  compared  with  that  of  nature, 
—  here  it  is  important  to  know,  if  possible,  whether  there  exists, 
side  by  side  with  our  selection,  this  other  influence,  in  some  cases 
assisting,  in  others  opposing,  our  aims. 

The  influence  of  the  environment  upon  transmission  is  cer- 
tainly slight  at  any  moment,  but  if  it  exists  at  all  it  is  cumulative, 
and,  being  independent  of  selection,  it  is  a  friend  to  the  breeder 
for  fixing  desirable  characters,  as  it  is  also  an  insidious  enemy,  to 
be  greatly  dreaded,  when  an  undesirable  character  is  involved. 

As  the  discussion  proceeds  the  student  must  realize  that  we 
are  looking  for  that  which  is  at  best  but  an  infinitesimal  incre- 
ment as  compared  with  the  larger  results  due  to  selection,  the 
presence  and  influence  of  which  he  must  grow  skillful  in  detect- 
ing and  assessing. 

He  must  also  be  upon  his  guard  against  evidence  that  is  not 
evidence.  For  example,  a  cat  learns  to  open  a  door,  or  a  mare 
to  hold  up  her  foot  for  her  feed.  If  the  young  develop  the  same 
habit  as  the  mother,  the  hasty  observer  calls  it  a  case  of  the 
inheritance  of  an  acquired  character ;  whereas  the  truth  is  that 
in  all  probability  the  young  creatures  simply  learned  it  by  obser- 
vation ;  indeed  the  readiness  of  the  young  to  learn  by  imitation 
is  vastly  underrated.  In  the  case  of  the  horse  it  must  also  be 
remembered  that  most  individuals  that  hold  up  the  foot  when 
begging  have  defective  voices.  This  defect  is  extremely  likely 
to  be  transmitted  to  the  young,  which,  finding  themselves  voice- 
less, would,  if  left  to  themselves,  even  entirely  without  example, 
resort  to  the  next  most  convenient  and  natural  method  of  beg- 
ging, which  is  holding  up  the  foot.  It  must  not  be  forgotten 
that,  in  the  horse,  holding  up  the  foot  in  begging  is  a  kind  of 
fundamental  instinct,  second  only  to  vocal  effort,  and  it  may 
be  said  in  general  that  if  a  horse  cannot  call  for  his  feed  he 
will  hold  up  his  foot.  Against  such  instances  as  these,  urged 


354 


TRANSMISSION 


as  proof  of  the  inheritance  of  acquired  characters,  the  student 
must  be  on  his  constant  guard,  and  he  must  be  extremely  care- 
ful in  the  generalizations  he  allows  himself  to  make  in  this  partic- 
ular field  of  study. 

This  subject  has  been  greatly  complicated  by  a  mass  of  tradi- 
tion that  has  grown  up  around  it.  The  average  man  assumes 
that  the  effects  of  environment  are  transmitted.  He  does  not 
stop  to  inquire  seriously  into  the  subject.  He  considers  all 
doubt  on  this  point  as  foolishness ;  but  that  which  he  considers 
as  good  proof  is,  in  many  cases  at  least,  anything  but  proof. 

As  if  this  were  not  enough,  the  naturalist  on  his  part  has  still 
further  muddled  the  matter  by  a  most  unfortunate  and  con- 
fusing, not  to  say  inaccurate,  use  of  terms.  Traditions  may  be 
ignored  for  purposes  of  study,  but  not  so  with  terminology, 
which  should  be  exact  and  accurate.  The  two  most  unfortunate 
terms  that  ever  crept  into  evolutionary  studies  are  "  congenital  " 
and  "  acquired." 

Characters  congenital  and  acquired.  It  is  a  custom  with 
evolutionists  to  assume  that  every  adult  individual  is  in  posses- 
sion of  two  kinds  of  characters  :  first,  those  which  were  born 
into  it  (the  congenital) ;  second,  those  which  were  forced  upon 
it  by  the  conditions  of  life  or  picked  up  as  the  result  of  experi- 
ence (the  acquired).  They  then  proceed  to  the  very  natural 
assumption  that  the  congenital  characters,  having  been  derived 
by  inheritance,  will  in  turn  be  transmitted ;  after  which  they 
raise  what  would  seem  to  be  the  final  question,  Are  the 
acquired  characters  transmitted  ?  Thus  is  the  field  of  discus- 
sion staked  out,  and  no  such  battle  royal  (of  words)  was  ever 
fought  out  in  modern  times  —  except  over  questions  theological 
—  as  has  been  waged  over  the  question  of  the  inheritance  (or 
transmission)  of  acquired  characters.1 

1  This  is  the  question  that  has  divided  the  neo-Lamarckians  and  the  neo- 
Darwinians,  and  almost  the  entire  host  of  evolutionists  for  the  last  twenty  years 
have  ranged  themselves  on  one  side  or  the  other  of  this  dispute  and  have 
allowed  themselves  to  be  identified  with  one  or  the  other  of  the  hostile  camps. 

As  the  special  opponent  of  the  theory  of  the  transmission  of  acquired  char- 
acters, the  student  should  read  Weismann,  particularly  his  Essays  on  Heredity, 
his  Germ  Plasm,  and  his  Germinal  Selection. 

The  most  vigorous  and  accessible,  if  not  the  most  able,  champion  of  the 
transmissionists  is  perhaps  Romanes  in  his  Examination  of  Weismannism  and 


TRANSMISSION   OF   MODIFICATIONS  355 

The  writer  does  not  propose  to  enter  the  disputed  territory 
at  this  point,  for  the  reason  that  he  does  not  believe  in  accept- 
ing for  these  purposes  the  fundamental  distinction  between 
"  congenital  "  and  "  acquired  "  characters.  The  use  of  the  term 
"congenital"  as  distinct  from  ''acquired"  is  most  unfortunate. 
Any  character  present  at  birth  is,  by  definition,  congenital.  The 
list  would  include  not  only  the  characters  typical  of  the  race  but 
also  malformations  and  deformities  due  to  conditions  in  utero  or 
to  unknown  causes.  Thus  men  have  been  born  without  feet,  yet 
the  chances  of  transmitting  the  deformity  are  extremely  remote. 
An  arm  or  a  leg  may  be  misplaced  during  embryonic  develop- 
ment and  malformations  result  without  essentially  bearing  upon 
Khe  conditions  that  are  supposed  to  control  inheritance. 
Manifestly  the  most  profitable  distinction  to  observe  regard- 
ng  the  inheritance  of  variations  is  a  strict  discrimination  be- 
ween  those  that  have  arisen  through  causes  affecting  the  germ 
plasm  directly,  on  the  one  hand  (blastogenic),  and  those  that 
affect  the  body  during  its  development,  upon  the  other  (somato- 
genic).  Now  an  accident  to  the  embryo  in  utero  is  as  much 
external  to  the  germ  plasm  —  the  inherited  substance  on  which 
development  depends  —  as  is  an  accident  after  birth,  and  there- 
fore distinctions  between  congenital  and  acquired  characters  are 
extremely  misleading,  especially  among  mammals ;  less  so,  of 
course,  among  birds,  in  which  no  such  thing  as  birth  exists. 

his  Darwin  and  After  Darwin.  Cope,  in  his  Primary  Factors  of  Organic  Evolution, 
may  be  read  with  profit,  as  may  Eimer  in  Organic  Evolution. 

Both  factions  claim  to  be  disciples  and  exponents  of  Darwin,  but  the  opponents 
of  transmission,  from  their  extreme  appeal  to  selection,  have  come  to  be  known  as 
neo-Darwinians,  and  the  advocates  of  transmission  have  accepted  the  name  of 
neo-Lamarckians,  from  their  belief  in  the  formative  influence  of  the  environment, 
which  was  the  distinguishing  feature  of  Lamarck's  view  of  evolution. 

In  general  it  may  be  said  that,  while  there  are  many  notable  exceptions,  the 
zoologists  tend  to  side  with  the  neo-Darwinians  against  the  idea  of  transmission, 
while  the  botanists,  dealing  with  fixed  and  of  necessity  much  more  plastic  forms, 
tend  to  go  with  the  neo-Lamarckians. 

In  the  opinion  of  the  writer,  Lloyd  Morgan  is  by  far  the  most  satisfactory 
investigator  and  writer  on  this  vexed  question,  especially  in  his  Habit  and 
Instinct,  which  should  be  read  by  every  careful  student  of  this  subject.  The 
inquiry  is  conducted  to  find  out  the  truth,  not  to  prove  or  to  disprove  the 
inheritance  of  acquired  characters,  and  his  conclusions  as  stated  on  pages  307-322 
of  that  volume  may  well  engage  the  attention  of  the  thoughtful  reader,  whatever 
his  personal  views  on  the  points  in  dispute. 


356  TRANSMISSION 

In  every  case,  bird  or  mammal,  plant  or  animal,  the  new  indi- 
vidual begins  with  the  fertilized  germ,  not  at  some  later  period 
called  birth  ;  and  for  our  purposes  the  distinction  should  not  be 
whether  the  variation  was  implanted  before  or  after  birth,  but 
whether  its  cause  was  internal  or  external  to  the  germ. 

Attention  should  be  fixed  upon  the  germ  plasm,  the  physical 
basis  of  life  and  the  only  known  avenue  of  transmission  from 
one  generation  to  the  next,  and  the  distinction  should  be  clearly 
made  between  variations  due  to  changes  in  its  structure  from 
internal  or  other  causes,  and  those  changes  of  the  organism 
due  to  influences  exerted  directly  upon  the  organism  during  its 
development.  As  this  discussion  proceeds  it  should  be  clearly 
borne  in  mind  that  no  character  can  be  transmitted,  no  matter 
how  strongly  present,  unless  the  germinal  matter  is  in  some  way 
previotisly  affected.  Nothing  else  passes  over  from  parent  to 
Offspring,  and  no  other  medium  of  transmission  is  possible.  The 
study  is,  therefore,  clearly  defined.  Do  modifications,  as  such, 
affect  the  .germ  directly,  and  so  become  transmitted  ;  or,  if  not, 
do  the  same  influences  that  affect  the  developing  individual 
also  affect  the  germinal  matter  in  the  same  direction,  giving  all 
descendants  an  initial  trend  or  modification  similar  to  the  one 
impressed  upon  the  parent  ? 

SECTION  II  — EVIDENCE  FROM  THE  NATURE  OF 
VARIATION 

In  the  opinion  of  the  writer  it  is  fundamentally  wrong,  both 
logically  and  biologically,  to  conceive  of  the  individual  as  made 
up  of  two  sets  of  faculties, — one  inherited  and  the  other 
acquired.  The  distinction  not  only  does  not  rest  upon  good 
ground,  but  in  its  application  to  the  facts  of  life  it  leads  to  most 
unfortunate  conceptions  and  to  most  erroneous  conclusions.  It 
is  this  fundamental  misconception  of  the  function  of  the  environ- 
ment that  is  responsible  for  most  of  the  foggy  thinking  which 
marks  the  contention  over  the  question  o*f  inheritance  of  acquired 
characters,  and  which  nowhere  else  bears  such  unfortunate  fruit 
as  in  the  field  of  practical  affairs.  In  general  evolution  it  does 
not  matter  greatly  whether  acquired  (?)  characters  are  inherited 


TRANSMISSION   OF   MODIFICATIONS  357 

much  or  little,  or  not  at  all ;  the  discussion  is  there  largely  an 
academic  question.  But  in  the  fields  and  yards  of  the  farmer  it 
is  the  largest  of  all  questions,  and  we  are  led  to  inquire  sharply 
whether  these  distinctions  are  real ;  whether  the  differences 
between  germinal  (blastogenic)  and  acquired  (somatogenic)  char- 
acters are  differences  in  kind  or  in  degree  ;  whether,  in  short, 
acquired  characters,  in  the  common  acceptation  of  the  term  and 
in  any  true  sense,  exist  at  all. 

The  characters  of  the  individual  are  the  characters  of  the  race. 
Careful  observation  will  disclose  the  fact  that  every  quality 
inherited  or  acquired  by  an  adult  individual  is  possessed  in  some 
degree  by  every  other  normal  adult  individual  of  the  same  race. 
All  horses  can  trot  some ;  all  cows  give  some  milk ;  all  sheep 
bear  wool  of  some  color,  length,  or  degree  of  fineness ;  all  hens 
have  feathers  ;  all  men  not  idiotic  can  learn  and  speak  a  lan- 
guage; all  men  have  some  little  (perhaps  very  little)  musical 
ability,  and  all  can  learn  to  play  the  piano  or  the  violin.  The 
point  here  is  not  whether  it  is  skillfully  done,  but  whether  it 
can  be  done  at  all. 

It  is  a  habit  of  speech  to  designate  a  low  degree  of  quality  by 
negative  terms,  and  we  say  of  the  horse  that  trots  but  slowly  or 
awkwardly  that  he  "  cannot  trot."  We  mean  by  that  that  he 
cannot  trot  well  enough  to  make  him  valuable  for  this  purpose. 
In  the  same  way  the  man  who  "  cannot  sing"  is  the  one  whose 
singing  we  do  not  care  to  hear;  the  man  who  "  cannot  speak" 
is  the  one  on  whom  we  would  not  depend  for  the  presentation 
of  a  difficult  case.  We  do  not  mean  of  him  that,  like  the  oyster, 
he  cannot  convey  information  and  is  dumb  because  of  the  utter 
absence  of  the  organs  and  powers  of  speech. 

So  these  are  relative  terms,  like  ."heat"  and  "  cold,"  but  our 
use  of  them  in  the  absolute  sense  has  built  up  in  the  popular 
mind  an  assumption  that  they  stand  for  realities,  not  relative 
values  of  the  same  thing ;  just  as  the  unlearned  man  supposes 
cold  to  be  as  real  as  heat,  and  black  (which  is  the  absence  of  all 
color)  to  be  as  real  as  white  (which  is  the  presence  of  all).  Thus 
have  we  by  our  verbiage  elevated  relative  values  to  absolute 
distinctions  in  kind,  creating  misconceptions  which  we  must  first 
undo  if  we  are  to  proceed  safely  in  this  study.  All  individuals 


358  TRANSMISSION 

of  the  same  race  possess  the  same  characters ;  herein  do   racial 
values  exist  and  hereby  are  racial  distinctions  established. 

Variation  practically  confined  to  racial  characters.  In  all  the 
examples  of  variation  that  have  been  cited, — and  they  have 
purposely  been  many,  —  and  in  all  the  cases  that  occur  in  our 
fields  and  yards,  variation  is  confined  to  racial  characters.  This 
is  the  experience  of  breeders  everywhere.  When  dealing  with 
cattle  breeding  all  variation  is  of  cattle  characters.  We  do  not 
expect  and  we  do  not  find  among  cattle  the  appearance  of  char- 
acters belonging  to  horses,  sheep,  pigs,  dogs,  or  chickens,— 
except  as  they  are  possessed  in  common.  The  same  is  true  of 
other  species,  and  when  characters  are  possessed  in  common 
the  variation  in  each  case  is  well  within  the  range  of  the  species 
in  question. 

That  is  to  say,  variations  in  cattle  all  appear  among  well- 
known  and  long-established  characters  that  distinctly  belong  to 
cattle,  such  as  the  head,  horns,  legs,  color,  udder,  quantity  or 
quality  of  milk,  etc.  Among  chickens  the  variations  are  among 
chicken  characters,  such  as  the  shape  and  color  of  feathers  ;  size, 
color,  and  quality  of  the  egg ;  quality  of  meat,  etc. 

We  find  neither  chicken  characters  appearing  among  cattle 
nor  cattle  characters  appearing  among  chickens.  The  hen  can- 
not give  milk,  nor  can  the  cow  bear  feathers.  There  is  no  inter- 
change of  characters  between  species,  either  by  birth  or  by 
acquisition  afterward.  Not  only  that,  but  even  when  the  same 
character  is  possessed  by  two  distinct  species  its  variations  in 
each  are  well  within  the  range  of  the  particular  species.  For 
example,  the  legs  of  cattle  and  chickens  are  built  upon  the  same 
general  plan,  but  they  have  drifted  far  apart,  and  do  not  overlap 
even  in  their  variations.  The  leg  of  a  horse  and  the  leg  of  a  cow 
are  on  nearly  the  same  plan,  and  yet  no  one  would  mistake  the 
one  for  the  other,  no  matter  what  the  range  of  variation.  Even 
color  deviations  are  always  within  certain  definite  limits. 

No  such  thing  as  an  acquired  character.  Variation  is,  there- 
fore, a  condition,  not  a  thing.  It  is  the  state  of  a  racial  character, 
not  the  result  of  the  introduction  of  a  new  one  ;  indeed,  variation 
by  the  introduction  of  a  positively  new  character  is,  if  not 
unknown  among  us,  a  matter  that  belongs  to  general  evolution 


TRANSMISSION   OF   MODIFICATIONS  359 

and  to  the  origin  of  races.  It  is  not  a  matter  that  practically 
concerns  the  thremmatologist,  who  is  working  with  established 
races  and  characters  whose  variations  are  fairly  well  circum- 
scribed. The  appearance  of  a  positively  new  character  among 
any  of  these  races  would  be  cause  for  profound  astonishment. 
Under  the  present  state  of  knowledge,  and  for  our  purposes, 
we  may  say  that  there  are  no  such  things  as  acquired  charac- 
ters, in  any  proper  sense  of  the  term.  It  is  a  figure  of  speech 
at  best,  and  a  most  unfortunate  one,  at  that. 

By  "  acquired  character,"  as  the  term  is  commonly  employed, 
is  always  meant  one  of  two  things,  —  (i)  differences  in  the 
degree  of  development  of  ordinary  racial  characters,  or  (2)  the 
peculiar  use  to  which  the  individual  has  put  his  natural  endow- 
ments under  his  special  conditions  of  life. 

These  are  differences  in  degree,  not  in  kind.  To  speak  of 
them  as  characters  is  to  dignify  them  with  a  term  whose  mean- 
ing is  eminently  qualitative,  not  quantitative,  and  this  it  is  that 
has  built  up  the  false  conception  that  individuals  of  the  same 
breed  or  race  differ  from  each  other  in  something  that  is  real ; 
that  individual  differences  are  all  qualitative, — whereas,  within 
the  race,  they  are  quantitative  merely. 

To  speak  of  these  differences,  which  are  only  differences  in 
degree  of  development  of  ordinary  racial  characters,  or  at  most 
only  differences  in  behavior  of  organs  and  parts  known  to  be 
able  to  respond  to  various  stimuli  and  to  function  somewhat 
differently  under  different  conditions,  —  to  speak  of  differences 
such  as  these  personal  acquisitions  as  acquired  characters,  is 
to  use  the  term  "character"  in  an  unfortunate  and  singularly 
misleading  sense. 

Now  a  difference  which  is  nothing  more  than  a  degree  of 
development  of  a  well-known  character  is  not  in  itself  a  new 
character.  It  is  not  in  that  sense  an  acquisition.  It  is  more 
in  the  nature  of  a  realization  of  what  was  before  a  potential 
possibility. 

Neither  is  a  habit  entitled  to  the  term  "  new,"  or  "  acquired," 
character.  Habit  refers  only  to  the  customary  use  of  natural 
faculties.  Some  characters,  like  those  associated  with  the  pro- 
duction of  the  gastric  juice,  for  example,  have  but  a  narrow 


360  TRANSMISSION 

functional  range  and  are  quite  out  of  control  of  the  individual ; 
others,  like  the  brain  and  the  hand,  are  capable  of  functioning 
in  many  directions, — so  many  that  no  lifetime  is  long  enough, 
or  its  needs  and  experiences  varied  enough,  to  exhaust  their 
possibilities. 

If  the  student  hopes  to  follow  the  mazes  of  racial  characters  as 
they  traverse  the  generations,  like  threads  through  the  patterns 
of  a  fabric,  he  must  not  confuse  either  his  terminology  or  his 
ideas  by  attaching  so  important  a  conception  as  "character" 
to  what  is  nothing  more  than  an  individual  manifestation  of 
character  development,  or  the  particular  personal  use  to  which 
many  racial  characters  may  be  put. 

The  faculties  of  the  individual  are  limited  in  kind  to  the 
faculties  of  the  race,  and  in  degree  to  the  intensity  of  their 
inheritance  and  the  conditions  of  life.  There  is  no  case  in 
which  an  individual  of  one  race  has  picked  up  or  otherwise 
acquired  a  character  that  belongs  to  another  race  and  not  to 
his  own.  All  his  achievements,  all  his  capacities,  are  within 
the  limits  of  his  racial  characters  and  the  conditions  controlling 
their  development. 

The  individual  is  in  actual  possession  of  all  the  characters  of 
the  race.  That  this  is  true  is  shown  by  breeding  experiences 
everywhere,  for  in  all  cases  the  individual  transmits  to  some 
degree  all  the  characters  of  his  race.  Milk  secretion  is  a  char- 
acter limited  to  mammals  and  functional  only  in  the  female  sex, 
yet  every  dairyman  knows  that  the  bull  will  transmit  milking 
qualities  as  successfully  as  will  the  cow. 

Our  experience  with  reversions  —  those  "  long-lost  charac- 
ters "  that  return  to  plague  us  —  is  convincing  proof  of  the  fact 
that  every  character  of  the  race  is  potentially  present  in  every 
individual,  whether  the  degree  of  development  be  much  or  little. 
In  no  other  manner  could  they  be  so  long  and  so  persistently 
preserved  in  the  race.  Their  repeated  appearance,  long  after 
they  have  ceased  to  be  typical,  only  shows  that  they  were  never 
truly  lost. 

The  individual  is,  therefore,  born  with  all  the  possibilities  of 
the  race  to  which  he  belongs.  Those  which  shall  develop  and 
fix  the  type  will  depend  upon  two  considerations,  —  first,  the 


TRANSMISSION  OF  MODIFICATIONS  361 

relative  intensity  of  their  inheritance,  and  second,  the  opportun- 
ities for  their  development. 

The  achievements  of  a  race  under  one  environment,  therefore, 
cannot  be  considered  as  limiting,  or  even  very  closely  indicating, 
its  possibilities  under  another,  and  we  never  know  the  possibili- 
ties of  a  race  until  we  have  seen  it  bred  and  reared  under  a 
great  variety  of  conditions,  —  all  of  which  is  but  another  way 
of  saying  that  vastly  more  is  present  and  transmitted  than  even 
keen  observers  are  aware  of.  Everything  that  belongs  to  the 
race  is  always  present  and  is  always  transmitted  in  some  degree. 
It  is  sheer  business  folly,  as  well  as  bad  science,  to  conceive  of 
characters  as  being  lost  for  generations,  then  appearing  again. 

Whatever  the  individual  comes  to  be,  therefore,  in  his  adult 
state,  he  is  to  be  regarded  as  the  repository  of  all  the  charac- 
ters of  his  race,  only  a  few  of  which  have  reached  anything 
like  their  highest  possible  development  in  his  particular  per- 
sonality, and  many  of  which  remain  so  undeveloped  as  to  be 
unnoticed  perhaps  throughout  his  entire  lifetime.  That  they  are 
potentially  present,  however,  is  attested  by  his  descendants. 

Highly  differentiated  races  are  so  rich  in  possibilities  and  so 
great  in  their  range  of  characters,  that  the  lifetime  of  any  indi- 
vidual is  too  short,  and  his  environment  too  circumscribed,  to 
realize  more  than  a  fraction  of  his  possibilities  ;  but  he  transmits 
the  remainder  as  an  undeveloped  heritage  to  his  descendants. 
WJiat  now,  if  any,  is  the  effect  upon  transmission,  of  the  particular 
development  that  he  has  realized  in  his  own  personality  f  Will 
the  special  characters  that  he  has  strongly  developed  be  transmitted 
with  increased  intensity  because  of  their  recent  extreme  develop- 
ment, or  will  this  development  have  no  effect  tipon  their  initial 
powers  in  the  next  generations  ?  This  is  the  one  question  we 
repeatedly  ask  ourselves,  for  it  is  the  one  we  most  desire  to 
answer. 

Degree  of  development  depends  upon  both  germinal  and  environ- 
mental influences.  The  evolution  of  a  mature  and  adult  individual 
from  a  fertilized  germ  is'  to  be  regarded  as  essentially  a  process 
of  development.  It  has  been  shown  that  all  differences  between 
adult  individuals  of  the  same  race  are  due  to  the  degree  of 
development  which  the  racial  characters  have  been  able  to  attain. 


362  TRANSMISSION 

This,  and  not  the  introduction  of  new  characters,  is  the  basis 
of  variation  between  individuals  of  the  same  race.  Differences 
between  races  may  be  either  qualitative  or  quantitative,  or 
both ;  but  differences  between  individuals  of  the  same  race  are 
essentially  quantitative. 

Quantitatively,  that  which  is  transmitted  from  parent  to  off- 
spring is  a  certain  capacity  for  development.  But  possession 
of  the  capacity  for  development  is  no  guaranty  that  development 
will  follow.  Whether  or  not  it  will  follow  depends  upon  the 
nature  of  the  conditions  of  life,  and  whether  they  will  afford  the 
opportunity  for  development. 

The  limits  of  development  of  any  racial  character  are  fixed, 
therefore,  by  two  factors  :  first,  the  initial  impulse  born  into  the 
individual,  the  intensity  of  which  is  a  matter  of  breeding ;  and 
second,  the  attitude  of  the  environment,  whether  favorable  or 
unfavorable. 

Manifestly  with  any  individual  the  highest  development  will 
be  in  those  characters  whose  inherited  intensity  is  strongest  and 
for  whose  development  the  environment  is  most  favorable.  Next 
in  order  will  come  those  with  high  intensity  but  which  are  forced 
to  struggle  against  an  unfavorable  environment,  as  well  as  those 
whose  inherited  intensity  is  less.  Weakest  of  all  will  be  the  de- 
velopment of  those  characters  whose  inherited  intensity  is  low  and 
for  which  the  environment  is  especially  unfavorable.  As  we  have 
seen,  no  matter  what  may  be  the  environment,  no  development 
will  take  place  except  along  lines  that  are  clearly  recognized 
as  within  racial  possibilities  and  therefore  due  to  transmitted 
impulses.  These  contingencies  cover  all  cases  of  variation 
between  individuals,  and  the  real  question  before  the  student 
is  not  whether  acquired  characters  are  inherited,  but  it  is  this  : 
Will  the  extreme  development  of  a  racial  character  under  unusu- 
ally favorable  conditions  of  life  augment  even  to  the  slightest 
degree  the  transmitted  tendency  for  development  in  the  next  gen- 
eration ?  or  are  intensities  the  product  only  of  changes  internal 
to  the  germ  plasm  ? 

Stated  more  broadly  the  question  is  this  :  Does  the  develop- 
ment attained  by  the  individual  influence  his  powers  of  transmis- 
sion ?  This  question  should  stand  out  clear-cut  in  the  student's 


TRANSMISSION   OF  MODIFICATIONS  363 

mind.  It  is  not  whether  an  individual  with  strong  tendencies  is 
a  better  breeder  than  one  with  weaker  tendencies,  —  that  is 
conceded;  it  is  not  whether  a  race  living  under  a  favorable 
environment  flourishes  better  than  one  living  under  hard  con- 
ditions,—  that  is  conceded,  too,  for  natural  selection  is  inevi- 
table ;  but  the  question  is,  whether  the  individual  will  be  the 
better  or  the  worse  as  a  breeder  because  of  the  special  develop- 
ment he  has  acquired. 

The  answer  to  this  will  decide  the  question  whether  we  shall 
keep  our  meat-breeding  animals  in  high  or  in  moderate  flesh ; 
whether  we  must  develop  the  speed  of  our  racing  stallions  and 
mares  ;  whether  a  given  sire  or  dam  is  a  better  breeder  after 
speed  is  developed  than  was  the  same  individual  when  green. 
It  will  determine  the  whole  matter  of  the  importance  of  develop- 
ing breeding  stock,  not  only  as  a  means  of  increasing  natural 
capacity,  but  as  a  means  of  intensifying  the  powers  of  trans- 
mission. 

Fortunately  we  are  not  without  facts  bearing  upon  this 
vexed  question ;  but  the  whole  field  is  exceedingly  difficult,  and 
reliable  evidence  is  eagerly  sought.  It  is  the  more  difficult  to 
secure  because  of  the  ever-present  and  always  powerful  influence 
of  selection. 

The  particular  modifications  (acquired  characters)  that  have 
been  most  discussed  and  whose  transmissibility  has  been  advo- 
cated on  the  one  hand  or  denied  upon  the  other  are  of  four 
distinct  kinds  : 

1.  Mutilations  due  to  injury  or  destruction  of  racial  characters 
after  they  have  reached  full  development. 

2.  Habits  of  life  arising  out  of  the  exigencies  of  existence. 

3.  Structural  peculiarities  due  to  use  and  disuse. 

4.  Adaptations  to  climatic  conditions. 

These  are  commonly  all  considered  as  acquisitions  in  the 
sense  of  additions  to  racial  characteristics.  In  the  view  advo- 
cated by  the  writer  they  are  all  reducible  either  to  different 
degrees  of  development  of  racial  characters,  or  to  the  uses  to 
which  these  are  put  under  the  conditions  and  exigencies  of 
life.  They  will  be  considered  in  the  order  named,  always  with 
the  question  uppermost  in  mind,  Are  they  transmissible  ? 


364  TRANSMISSION 

SECTION   III  — EVIDENCE  FROM  MUTILATIONS 

Mutilation  is  the  forcible  removal  of  a  part  after  it  has  de- 
veloped, or  at  least  the  destruction  of  those  parts  which  are  fully 
endowed  with  the  power  of  complete  development.  Unfortu- 
nately, in  this  field  the  most  absurd  stories  have  gained  credence, 
and  their  popular  acceptance  has  done  much  to  obscure  the 
whole  subject.  Some  one  owned  a  cat  whose  tail  was  pinched 
off  in  a  door,  and  straightway  all  her  kittens  were  tailless.  A 
few  semi-traditional  stories  like  this  are  made  the  foundation  for 
believing  in  the  transmission  of  mutilations,  the  facts  being  for- 
gotten that  for  generations  it  has  been  the  custom  to  remove 
the  tails  from  lambs,  with  no  sign  yet  of  tailless  sheep  as  a 
result,  and  that  circumcision  has  been  practiced  by  many  tribes 
from  the  remotest  times,  and  by  the  Jews  certainly  for  four 
thousand  years,  apparently  without  effect  upon  the  natural  de- 
velopment of  parts.  Certainly,  if  any  effect  has  been  produced, 
it  is  not  evident,  and  is  so  small  as  to  be  classed  among  negli- 
gible quantities,  falling  entirely  outside  the  field  of  practical 
results. 

The  tail,  being  a  portion  of  the  vertebral  column,  might  be 
expected  to  long  resist  all  influences  toward  its  suppression ; 
but  the  prepuce  is  an  unimportant  and  recent  structural  addi- 
tion, yet  still  it  lingers,  despite  persistent  and  systematic 
removal  by  force. 

The  question  lies  deeper  than  the  surface.  A  mutilation,  like 
any  other  difference,  in  order  to  be  transmitted,  must  first 
effect  the  germ  plasm,  which  is  the  only  material  carried  over. 
If  Darwin's  theory  of  gemmules  were  true,  then  it  might  be  con- 
ceivable that  a  defective  part  would  no  longer  produce  its  share 
of  the  germ  plasm,  and  that  it  would  certainly  disappear  from 
the  race,  and  that  at  once.  The  fact  that  persistently  mutilated 
parts  do  not  disappear  is  good  proof  not  only  that  mutilations 
are  not  transmitted,  but  that  the  theory  of  gemmules  is  incorrect. 

For  the  most  part,  belief  in  the  inheritance  of  mutilation  has 
rested,  not  upon  experimental  evidence,  but  upon  instances  in 
which  natural  deformities  in  the  offspring  correspond  to  muti- 
lations in  the  parents.  Such  correspondence  is  assumed  to  be 


TRANSMISSION   OF  MODIFICATIONS  365 

proof  of  a  causative  relation,  so  quick  are  we  to  accept  for  fact 
that  which  is  not  only  plausible  but  startling.  In  this  way  a 
mass  of  evidence  (?)  has  accumulated  on  this  subject  second  in 
amount  only  to  that  bearing  upon  birthmarks  and  upon  the 
"  control  of  sex." 

The  law  of  chance.  Before  subjects  of  this  character  can 
be  properly  studied,  the  operations  of  the  mathematical  law  of 
chance  must  be  comprehended  and  their  effects  deducted. 

If  we  toss  a  coin  the  odds  are  even  that  "  heads  "  will  be  up ; 
they  are  also  even  for  "  tails  up."  There  being  but  one  alterna- 
tive, either  heads  or  tails  is  certain  to  appear.  When  the  next 
toss  is  made  the  odds  are  again  even,  but  there  is  no  causative 
relation  between  the  first  and  second  events.  They  may  agree 
or  they  may  differ;  that  is,  both  may  be  heads,  both  may  be 
tails,  or  one  may  be  heads  and  the  other  tails. 

Successive  tosses  will  give  rise  to  an  extremely  irregular 
series,  as  may  be  shown  by  trial.  However,  if  the  series  be 
continued  indefinitely  and  tally  be  kept,  it  will  be  found  that  in 
the  long  run  the  heads  and  the  tails  will  be  equal.  When  the 
equality  will  first  occur  is  entirely  uncertain.  It  may  be  at  the 
second  throw  or  it  may  be  at  the  hundredth,  or  even  later,  but 
it  is  certain  to  come. 

The  roulette  wheel,  as  commonly  used,  is  made  up  of  thirty- 
seven  color  spaces,  eighteen  red  and  nineteen  black,  or  the 
reverse.  The  wager  is  laid  upon  the  number  or  the  color  on 
which  the  wheel  will  rest  after  a  supposedly  impartial  spin.  It  is 
evident  that  the  probability  of  its  resting  upon  a  particular  num- 
ber is  but  one  in  thirty-seven  if  the  wheel  is  mechanically  per- 
fect, and  that  the  chances  of  its  resting  upon  a  particular  color^ 
are  not  quite  even.  This  difference  of  nineteen  to  eighteen 
constitutes  the  ''advantage"  of  the  owner  over  the  player,  and 
shows  the  hopelessness  of  attempting  to  "  break  the  bank." 
This  margin  of  one  out  of  every  thirty-seven  bets  is  over  2.5 
per  cent  of  the  business  and  constitutes  the  assured  profit  in  a 
game  of  chance  conducted  honestly  on  this  plan,  —  which  is 
the  one  in  use  at  Monte  Carlo,  the  greatest  gambling  house  in 
the  world.1 

1  See  Pearson,  Chances  of  Death,   pp.  42-62. 


366  TRANSMISSION 

The  successions  of  red  and  black  representing  gain  and  loss 
are  so  irregular  and  so  confusing  that  the  player  fails  to  detect 
the  ratio  of  more  than  5  per  cent  that  is  against  him,  and  con- 
sequently does  not  realize  that  the  longer  he  plays  the  more 
certain  are  his  losses.  Nor  does  he  realize  that  in  the  long  run 
nothing  is  more  absolutely  certain  than  the  law  of  chance.  The 
deviation  is  not  great  at  any  point  after  the  first  few  throws, 
and  herein  lies  the  first  deceptive  quality  of  all  games  of  chance. 

If  the  letters  of  the  word  "  incomprehensibility  "  be  tossed 
into  the  air  in  such  a  manner  that  they  must  fall  into  a  line,  the 
chances  of  their  falling  in  the  proper  order  to  spell  the  word 
correctly  are  exceedingly  remote,  yet  it  is  bound  to  happen  if  the 
trials  are  long  enough  continued. 

These  simple  facts  teach  us  not  to  attach  too  much  impor- 
tance to  occasional  occurrences,  however  strange  or  apparently 
improbable.  They  teach  us,  too,  that  there  may  be  no  special 
cause  at  the  bottom  of  the  occurrence  beyond  the  mathematical 
law  of  probability.  The  tossing  of  coins  shows  why  it  is,  for 
example,  that  every  theory  for  the  control  of  sex  that  ever  has 
been  or  ever  can  be  invented  has  been  repeatedly  verified. 
There  is  but  one  alternative,  and  every  assumption  of  cause, 
however  absurd,  is  certain  to  come  true  (?)  half  the  time,  which 
is  sufficient  proof  for  most  people  who  depend  upon  memory 
impressions  rather  than  upon  absolute  records. 

Proof  by  the  method  of  instance  is  therefore  extremely 
hazardous.  Something  more  than  the  mere  fact  of  coincidence 
is  necessary  in  order  to  establish  a  causative  relation  with  any 
very  high  degree  of  certainty. 

When,  therefore,  a  deformity  in  a  child  corresponds  to  a  muti- 
lation in  a  parent  we  are  not  warranted  in  at  once  assuming  a 
causative  relation.  We  are  to  remember  that  deformities  of  all 
kinds  are  comparatively  common;  that  mutilations  are  exceed- 
ingly so ;  that  frequently  a  mutilation  will  resemble  a  natural 
deformity  or  an  injury ;  and  that  occasionally,  under  the  laws  of 
probability,  the  mutilation  of  the  parent  will  resemble  the 
deformity  in  the  offspring,  thus  suggesting  direct  transmission. 
We  are  to  remember,  too,  that  the  law  of  chance  must  first  be 
satisfied  before  we  can  assume  causation. 


TRANSMISSION   OF  MODIFICATIONS  367 

The  most  direct  way  of  procedure  is,  however,  not  to  endeavor 
to  eliminate  the  law  of  chance,  but,  by  direct  experiment, 
to  learn  whether  a  sufficient  number  of  occurrences  can  be 
established  to  clearly  exceed  in  number  any  possible  coincidence. 

Experimental  evidence  on  inheritance  of  mutilations.  The 
facts  just  given  show  conclusively  the  hazard  of  framing  theories 
on  chance  occurrences,  and  demonstrate  the  practical  worthless- 
ness  of  all  but  experimental  evidence  in  the  study  of  inheritance. 

Unfortunately  but  little  evidence  of  this  kind  is  at  hand,  and, 
so  far  as  is  known  to  the  writer,  that  which  is  at  hand  is  confined 
to  artificial  injuries  to  the  nerve,  with  exception  of  that  already 
cited  in  such  practices  as  docking  and  circumcision. 

Romanes  outlines  seven  classes  of  abnormalities  that  appeared 
in  the  offspring  of  guinea  pigs  corresponding  to  those  artificially 
produced  in  the  parents  by  Brown-Sequard  and  his  assistants. 
They  are  in  brief  as  follows  : 1 

1.  Appearance  of  epilepsy,  when  parents  have  been  rendered 
epileptic  by  an  injury  to  the  spinal  cord. 

2.  Same,  when  the  injury  had  been  to  the  sciatic  nerve. 

3.  Change  in  the  shape  of  ear  in  animals  born  of  parents  in 
which  such  a  change  was  the  effect  of  a  division  of  the  cervical 
sympathetic  nerve. 

4.  Partial  closure  of  the  eyelids  in  young  born  of  parents  in 
which  that  state  of  the  eyelids  had  been  induced  by  section  of 
the  cervical  sympathetic  nerve  or  the  removal  of  the  superior 
cervical  ganglion. 

5.  Exophthalmia  in  young  born  of  parents  in  which  a  similar 
protrusion  of  the  eyeball  had  been  produced  by  injury  to  the 
restiform  body. 

6.  Gangrene  of  the  ears  in  animals  whose  parents'  ears  had 
been  affected  by  injury  to  the  restiform  body. 

7.  Absence  of  toes  in  young  whose    parents  had  eaten  off 
their  toes,  which  had  become  "  anaesthetic  "  by  reason  of  the 
section  of  the  sciatic  nerve  alone  or  of  that  nerve  and  the  crural. 

8.  Various  morbid  states  of  the  skin  and  hair  corresponding 
to  a  similar  condition  of  the  parents  which  had  been  brought  on 
by  an  injury  to  the  sciatic  nerve. 

1  Romanes,  Darwin  and  After  Darwin,  II,  103-122. 


368  TRANSMISSION 

It  is  notable  that  all  these  experiments  are  based  upon  injury 
to  the  nerve  and  are  of  a  degree  of  severity  likely  to  affect  the 
entire  organism  seriously.  If,  however,  it  is  true  that  injury  of 
any  kind  in  the  parent  leads,  as  Brown-Sequard  and  Romanes 
evidently  suppose,  to  corresponding  deformities  in  the  offspring, 
the  fact  is  exceedingly  significant.  This  is  a  field,  however, 
quite  different  from  that  of  ordinary  injuries  —  such  as  the 
removal  of  a  horn  or  a  tail,  producing  no  constitutional  disturb- 
ance and  leading  to  no  organic  changes.  Further  experiments 
are  greatly  needed  to  confirm,  deny,  or  modify  the  results  of 
Brown-Sequard.  In  the  meantime  it  seems  almost  incredible 
that  so  much  erroneous  tradition  should  have  grown  up  sur- 
rounding this  matter  of  inherited  mutilations,  especially  when 
the  world  for  unknown  generations  has  almost  invariably  seen 
perfect  children  born  from  one-armed,  one-legged,  and  otherwise 
mutilated  parents.  Indeed,  if  offspring  inherited  the  ordinary 
mutilations  of  their  parents,  the  world  would  have  become  long 
since  a  collection  of  monstrosities  which  would  put  to  shame  the 
rare  specimens  now  collected  in  dime  museums. 

Inheritance  of  disease.  The  old  tradition  of  inheritance  of  dis- 
ease is  long  since  disproved,  and  those  diseases  once  thought 
to  be  inherited  are  now  known  to  arise  not  from  inheritance 
but  from  infection  after  birth,  which  for  obvious  reasons  is  ex- 
tremely easy  between  parent  and  offspring. 

The  weakening  effect  of  wasting  diseases  upon  the  parents, 
and  the  influence  of  this  weakening  upon  the  constitution  of  the 
offspring,  inducing  predisposition  to  disease,  is,  however,  quite 
another  matter.  That  many  of  the  effects  of  such  a  disease  of 
the  parents  will  work  injury  and  weakness  to  the  offspring  will 
be  readily  admitted  ;  that  such  offspring  will  be  the  more  sus- 
ceptible to  attack  from  diseases  of  all  kinds  will  hardly  be 
denied ;  but  whether  it  will  be  peculiarly  susceptible  to  the  spe- 
cial disease  that  wrought  havoc  with  the  parent  is  a  question 
on  which  we  need  much  more  evidence. 

Up  to  date  this  point  has  not,  in  the  opinion  of  the  writer, 
been  established.  Although  it  is  true  that  certain  family  lines 
are  specially  susceptible  to  tuberculosis,  it  is  not  yet  shown 
whether  this  susceptibility  is  the  result  of  inroads  of  this  special 


TRANSMISSION   OF   MODIFICATIONS  369 

disease  or  whether  it  is  caused  by  weakness  in  family  lines  des- 
tined to  disappear,  and  for  whose  extinction  tuberculosis  is  the 
special  agent  of  natural  selection.  The  weight  of  evidence  inclines 
the  writer  to  a  belief  in  progressive  immunity  from  diseases  of  this 
class, — a  matter  touched  upon  under  the  subject  of  acclimati- 
zation. That  the  spavined  mare  will  not  transmit  her  spavin  is 
as  fortunate  as  it  is  true,  but  the  question  lying  back  of  this 
fact  is,  Why  was  she  spavined  ?  Is  the  injury  an  evidence  of 
weakness,  or  is  it  only  the  result  of  an  accident,  such  as  might 
have  happened  to  any  horse  ?  If  it  is  the  former,  then  the 
weakness,  not  the  spavin,  will  be  transmitted  ;  if  it  is  the  latter, 
there  is  in  all  probability  not  the  slightest  danger.  If  injuries  of 
this  sort  were  transmissible,  our  horses  would  long  since  have 
acquired  a  collection  of  spavins,  ringbones,  splints,  sidebones, 
and  curbs  such  that  no  leg  could  hold  them.  It  is  far  from  the 
purpose  of  the  writer  to  advocate  the  use  of  defectives  as 
breeders,  but  we  cannot  close  our  eyes  to  the  fact  that  a  mare 
which  has  seen  hard  service  and  bears  the  marks  of  it  is  in  all 
likelihood  a  better  breeder  than  another  that  has  never  been  put 
to  the  test,  no  matter  how  clean  and  free  from  blemishes  the 
limbs  of  the  latter  may  be.  The  stubborn  fact  is  that  the  risk 
of  accident  is  so  great  that  a  horse  put  to  hard  service  is  certain 
to  be  blemished  sometime ;  and  so  far  as  present  knowledge  goes, 
she  is  as  good  a  breeder  after  the  accident  as  she  was  before,  — 
which  is  far  from  saying  that  every  blemished  horse  is  fit  for 
breeding  purposes. 

The  writer  is  clearly  of  the  opinion  that,  even  with  the  ex- 
periments of  Brown-Sequard  in  mind,  the  evidence  warrants 
the  conclusion  that  ordinary  injuries  to  the  body  are  not  trans- 
mitted to  the  offspring.  Whether  different  results  follow  those 
profound  injuries  that  reach  the  nerve  centers  and  work  con- 
stitutional changes  in  the  organism  is  a  matter  on  which  we 
must  await  further  evidence. 

Mutilations  have  reference  to  characters  already  fully  devel- 
oped, and  therefore  fully  provided  for  in  the  germinal  matter. 
If  violent  removal  is  to  lead  to  their  suppression,  it  must  lead  to 
it  through  some  sort  of  retroactive  influence  affecting  the  germ 
in  exactly  the  proper  particular  and  no  other,  —  a  presumption 


370  TRANSMISSION 

that  is  inconceivable  under  any  law  of  physiology  that  is  known 
or  that  can  be  imagined. 

The  non-development  of  parts  is  another  and  quite  a  different 
matter.  If  the  non-development  be  due  to  a  defective  germ,  it 
of  course  does  not  come  under  the  present  inquiry.  If,  however, 
it  be  due  to  an  injury  at  an  early  stage,  resulting  in  arrested 
development,  it  may  or  may  not  be  equivalent  to  a  mutilation. 
If  the  non-development  be  due  to  the  destruction  of  cells,  as 
in  chemical  dehorning,  it  is  to  all  intents  and  purposes  a  mutila- 
tion, as  conditions  were  present  for  full  development.  If  the 
non-development  be  due  to  malnutrition,  the  case  is  different, 
and  belongs  among  cases  to  be  considered  later. 

The  essential  weakness  of  the  whole  theory  that  mutilations 
may  be  transmitted  lies  in  the  fact  that  the  characters  in  question 
are  present,  fully  developed  and  functional,  until  removed  by  vio- 
lence, all  of  which  is  conclusive  evidence  of  a  natural  capacity 
for  complete  development.  In  view  of  our  inability  to  conceive 
how  the  removal  of  a  part  can  possibly  affect  the  corresponding 
portion  of  an  undeveloped  and  even  unfertilized  germ ;  in  the 
absence  of  reliable  experimental  data  and  with  the  certainty  that, 
were  the  injuries  due  to  the  multitude  of  accidents  occurring  to 
all  forms  of  life  transmitted  all  species  would  soon  be  disfigured 
by  an  overwhelming  mass  of  inherited  mutilations,  — in  view  of 
all  these  facts  we  are  certainly  warranted  in  feeling  assured  that 
injuries  to  the  fully  developed  body  are  not  transmitted. 

SECTION  IV  — EVIDENCE  FROM  FOOD  SUPPLY 

This  is  a  very  different  matter  from  mutilation.  Of  all  the 
conditions  of  life  this  is,  par  excellence,  the  limiting  element,  not 
only  in  body  building  and  in  functional  activity,  but  in  constitu- 
tional vigor  as  well. 

That  the  amount  of  food  available  is  a  controlling  factor  in 
the  development  of  size  is  a  matter  too  well  known  to  require 
discussion.  In  the  presence  of  abundant  food,  animals  and  plants 
of  all  species  attain  their  maximum  size  and  their  maximum 
development  in  all  respects.  If  the  supply  be  limited,  the  effect 
is  invariably  seen  in  under-development,  even  though  the  total 


TRANSMISSION  OF  MODIFICATIONS  371 

amount  consumed  is  many  times  greater  than  that  actually  used 
in  body  building. 

In  acclimating  to  a  shortened  food  supply  the  animal  or  plant 
is  forced,  not  so  much  to  make  more  economical  use  of  what  it 
can  obtain  as  to  reduce  the  scale  of  living  and  actually  to  accom- 
plish less  in  the  way  of  growth  and  functional  activity  generally. 
A  starving  animal  or  plant  will  make  the  most  of  all  available 
food,  but  in  addition  the  animal  will  replace  a  large  share  of  the 
dry  matter  of  the  body  with  water  and  reduce  its  activity  to  a 
minimum  before  it  succumbs,  and  a  starving  plant  will  still  put 
forth  new  leaves,  using  the  substance  of  the  old  to  nourish 
the  new. 

If  the  shortage  in  food  comes  before  development  is  complete 
its  effect  is  seen  in  under-development,  or  possibly  in  arrested 
development, — recognized  by  the  farmer  under  the  term 
"  stunted."  Sometimes  the  condition  is  only  temporary,  but 
more  often  it  is  permanent,  when  no  amount  of  food  later  in  life 
will  avail  to  repair  the  damage  done  by  shortage  during  devel- 
opment. Farmers  accordingly  recognize  the  period  of  growth 
as  a  "  critical  period,"  and  uniformly  say  that  if  any  live  stock 
is  to  be  short  of  feed  let  it  be  the  older  ones.  Sad  experience 
has  taught  the  irreparable  evil  of  shortage  in  food  during 
development. 

Under-nourishment  strikes  at  the  very  root  of  life  as  well  as 
at  development.  What  is  true  of  individuals  seems  true  of 
races.  Under-nourishment  is  followed  by  a  lowering  of  tone 
and  a  lessened  rate  of  living,  while  full  feed  and  maximum  con- 
ditions of  life  generally  induce  great  protoplasmic  activity  and 
rapid  cell  division,  resulting  in  maximum  size  and  maximum 
functional  activity  in  all  parts  of  the  structure. 

All  experience  goes  to  show  that  weakened  parents,  plant  or 
animal,  give  rise  to  young  that  are  low  in  vigor  and  slow  of 
growth.  Seed  corn  that  is  below  the  normal  in  vitality,  though 
it  may  germinate,  will  give  rise  to  weak  and  slow-growing  plants. 

There  are  all  degrees  of  vigor  and  intensity  of  the  vital 
processes,  from  zero  up,  and  nothing  seems  more  potent  than 
the  food  supply  in  influencing  this  matter  that  lies  at  the  basis 
of  all  development  and  all  functional  activity. 


372 


TRANSMISSION 


As  temperature  is  an  all-pervading  influence  with  smaller 
organisms,  so  is  food  an  all-pervading  influence  with  all  organ- 
isms, large  or  small.  Without  doubt  it  exerts  a  controlling  effect 
upon  the  quality  of  germinal  matter  produced,  as  it  does  upon 
its  quantity,  and  upon  the  maximum  or  minimum  development 
of  the  body. 

Constitutional  vigor,  which  is  the  most  valuable  asset  of  any 
plant  or  animal,  is  a  heritage  whose  seat  is  in  the  germ  from 
which  it  was  developed.  Such  a  germ  could  be  produced  only! 
by  a  vigorous,  healthy,  well-nourished  parent.  Anything  which 
weakens  this  parent  constitutionally,  which  lowers  its  tone, 
reduces  its  vital  powers,  and  lowers  its  rate  of  living,  must 
of  necessity  affect  the  quality  of  any  germinal  matter  it  may 
produce  and  the  constitutional  vigor  of  its  descendants. 

We  do  not  permit  this  condition  to  any  large  extent  in  our 
domesticated  species,  plant  or  animal,  for  we  realize  too  well 
the  consequences,  but  we  have  only  to  look  among  the  underfed 
classes  and  races  of  humans  to  see  the  evil  effects  of  malnutri- 
tion in  weakened  constitutions,  low  vitality,  predisposition  to  the 
ravages  of  disease,  and  general  inefficiency  wherever  any  great 
functional  activity,  physical  or  mental,  is  required.  That  this 
condition  is  transmitted  does  not  admit  of  a  reasonable  doubt. 

On  the  other  hand,  races  that  are  well  nourished  for  many 
generations  undergo  maximum  development.  This  has  been  the 
experience  with  all  domesticated  animals  and  plants.  For  the 
most  part  they  have  been  provided  with  all  the  food  they  needed, 
and  they  have  responded  with  a  development  such  as  never 
came  to  them  under  natural  conditions. 

Nature  never  produced  such  specimens  as  our  modern  beef 
or  milk  breeds  or  our  draft  horses.  Our  achievement  as  breed- 
ers is  due,  therefore,  to  something  besides  selection,  and  we  are 
forced  to  one  of  three  conclusions  : 

1.  That  nature  never  produced  a  perfect  specimen;  that  is, 
that  natural  conditions  were  never  sufficiently  favorable  to  allow 
the  individual  to  realize  the  full  development  to  which  his  natural 
endowments  entitled  him. 

2.  That  with  each  increment  of  gain  through  selection,  estab- 
lishing a  higher  general  average,  a  new  "  center  of  variation  " 


TRANSMISSION   OF  MODIFICATIONS  373 

was  also  established,  which  was  bound  in  time  to  produce  better 
specimens  than  ever  before. 

3.  That  there  has  been  direct  transmission  of  the  increased 
vigor  and  powers  of  nutrition  and  growth  that  come  from  full 
feed. 

The  first  conclusion  is  unthinkable.  Nature  must  certainly 
have  produced,  occasionally  at  least,  perfect  specimens  of  their 
kind,  and  the  belief  that  this  is  so  is  favored  by  the  fact  that 
wild  things  do  not  respond  generously  to  full  feed. 

The  second  is  without  doubt  a  real  fact  in  evolution,  difficult 
as  it  is  to  comprehend.  Later,  in  statistical  studies,  it  will  be 
found  to  our  satisfaction  that  as  the  average  is  raised  by  selec- 
tion new  values  appear  at  the  top,  —  a  fact  on  which  depends, 
without  doubt,  a  large  share  of  our  improvement  of  all  species. 

And  yet  we  cannot  fight  off  the  conviction  that  here,  at  this 
point,  lying  so  close  to  the  very  springs  of  life,  the  absolute  con- 
dition of  life  —  nutrition  —  exerts  a  controlling  influence  upon 
that  mysterious  force  which  we  call  the  vital  principle,  and  whose 
relative  strength  we  measure  by  such  terms  as  "constitution" 
and  "vigor."  That  vigor,  or  the  lack  of  it,  is  a  transmissible 
character  no  one  will  deny,  or  even  doubt ;  and  it  is  the  firm 
conviction  of  the  writer  that  when  this  vigor,  or  scale  of  living, 
has  been  strengthened  or  weakened  from  any  cause,  the  power 
of  the  individual  to  transmit  a  vigorous  constitution  to  its  off- 
spring will  be  enhanced  or  lessened  accordingly,  and  that  when 
the  last  word  shall  have  been  spoken  upon  the  disputed  ques- 
tion of  inheritance  or  non-inheritance  of  acquired  characters  it 
will  be  found  to  square  with  this  fact. 

The  writer  desires,  above  all  things,  not  to  dogmatize.  Facts, 
not  opinions,  are  needed  in  these  uncertain  fields  ;  and  yet,  until 
the  partisan  advocates  of  the  opposite  sides  of  this  question  will 
divide  the  question  and  discuss  separately  the  three  or  four  dis- 
tinctly different  issues  involved,  —  until  that  time,  practical 
breeders  must  not  be  deceived  or  lulled  into  carelessness  by  the 
dictum  that  "  acquired  characters  are  not  transmitted." 

Increased  development  above  the  natural  in  one  form  or 
another  is  the  principal  object  in  all  improvement,  and  a  large 
share  of  the  possibility  of  such  increased  development  lies  in 


374  TRANSMISSION 

this  matter  of  constitutional  vigor,  which  so  largely  depends 
upon  nutrition  that  the  breeder  can  afford  to  make  no  mistake 
at  this  point. 

Influences  that  strike  at  the  root  of  the  vital  principle,  what- 
ever that  may  be,  are  far  reaching  in  their  consequences.  To 
maintain  the  vital  powers  at  a  maximum  is  one  of  the  prime 
objects  in  all  breeding,  and  that  this  is  to  a  large  extent  a 
matter  of  nutrition  is  a  fact  that  should  be  fully  appreciated 
by  him  who  hopes  to  maintain  unimpaired  the  valuable  racial 
characters  for  which  he  breeds  his  animals  and  his  plants. 

There  is  no  better  maxim  for  the  breeder  than  this  :  the 
results  of  good  feed  are  transmitted  to  the  offspring  in  the  form 
of  a  vigorous  constitution  and  large  powers  of  assimilation  and 
of  service. 


SECTION  V  — EVIDENCE  FROM  ACCLIMATIZATION 

It  is  a  well-known  fact  that  the  individual  acquires  by  experi- 
ence a  high  degree  of  resistance  to  temperature,  poisons,  or 
other  adverse  conditions  of  life  ;  that  this  modification  is  more 
or  less  permanent  with  the  individual  and  that  in  good  time  the 
race  as  a  whole  becomes  acclimatized  to  changed  but  persistent 
conditions.1  Is  this  race  acclimatization  in  any  way  the  result 
of  transmission  of  the  acclimatization  of  the  individual  ? 

1  It  should  be  clearly  understood  that  "  acclimatization "  is  not  confined  to 
adverse  conditions ;  it  may  relate  as  well  to  adaptation  to  improved  conditions, 
such  as  increased  food  supply.  Indeed,  the  term  is  intended  to  cover  accommo- 
dation to  any  change  in  external  conditions  of  life,  whether  favorable  or  unfavorable, 
gradual  or  sudden. 

As  is  well  known,  acclimatization  is  more  successful  if  the  subjection  be 
gradual ;  but,  in  any  event,  one  of  two  results  will  follow  if  the  individual  is  not 
killed  in  the  process:  (i)  it  will  become  permanently  altered,  and  will  therefore 
discharge  its  functions  in  a  modified  manner ;  or  (2)  it  will  acquire  by  experience 
so  high  a  degree  of  resistance  as  to  be  able  to  resume  its  usual  activities  after 
the  first  disturbance  and  afterward  to  discharge  its  normal  functions  in  spite  of 
adverse  conditions. 

There  are  thus  two  kinds  of  acclimatization  :  one  in  which  the  functions  or 
activities  are  modified,  the  other  in  which  the  individual  succeeds  in  resisting  the 
changed  conditions,  and  therefore  in  preserving  its  normal  functions.  Of  the 
two,  the  latter  is  perhaps  the  more  common.  The  former  betrays  the  more  con- 
stitutional change,  the  latter  the  greater  elasticity  in  organization. 


TRANSMISSION  OF   MODIFICATIONS  375 

To  determine  whether  in  the  acclimatization  of  a  race  agen- 
cies are  involved  other  than  selection  operating  upon  individuals, 
it  is  necessary  either  to  eliminate  the  results  due  to  selection  or 
else  to  discover  cases  in  which  it  does  not  occur.  While  the 
first  is  all  but  impossible  of  accomplishment  with  any  feeling  of 
assurance,  the  second  is,  in  the  opinion  of  the  writer,  entirely 
feasible,  especially  in  certain  lines. 

The  importance  of  the  whole  question  and  the  difficulty  of 
securing  reliable  data  are  sufficient  excuse  for  introducing  a 
somewhat  full  discussion  of  certain  topics  which  afford  evidence 
upon  the  question  at  hand. 

Extent  of  acclimatization.  The  power  of  the  individual  to 
adapt  itself  to  changed  conditions  is  something  marvelous,  as 
has  been  seen  under  the  subject  of  causes  of  variation  and  in  the 
discussion  of  relative  stability.  This  same  elasticity  of  organi- 
zation is  characteristic  of  races  as  a  whole.  By  means  of  this 
adaptability  many  species  of  both  animals  and  plants  have 
totally  changed  their  habitat,  and  with  this  change  have  under- 
gone the  most  sweeping  alterations.  The  whale  is  developed 
from  a  land  mammal  and  is  suffering  degeneracy  as  a  conse- 
quence. Swine  have  been  adapted  from  a  diet  of  roots  and 
flesh  to  one  mainly  of  grain.  Horses  and  cattle  in  their  wild 
state  subsisted  entirely  on  pasture,  but  with  us  their  diet  is 
from  25  to  75  per  cent  grain.  Sheep  are  mountain  animals,  but 
they  have  been  adapted  to  the  richest  pastures  and  the  lowest 
plains.  The  turkey,  native  to  North  America,  is  making  his 
way  over  all  the  earth,  as  chickens  have  scattered  broadcast 
from  their  native  habitat  in  southeastern  Asia. 

The  potato,  native  to  the  mountains  of  Peru,  is  now  grown 
everywhere  in  temperate  regions,  though  it  never  succeeded  in 
acclimating  in  the  tropics  except  in  high  altitudes.  There  are 
evident  limits,  or  else  the  possibilities  are  not  yet  exhausted. 

Corn  (maize)  will  endure  but  slight  change  in  locality  without 
suffering  seriously,  yet  after  a  few  years  it  appears  to  recover 
tone  and  succeed.  In  this  way  the  culture  of  this  crop  has  been 
gradually  moving  northward  in  the  United  States,  until  now  it 
is  fully  acclimated  in  regions  in  which  a  quarter  of  a  century  ago 
its  culture  was  impossible.  So  sensitive  is  the  corn  plant  to 


376  TRANSMISSION 

climatic  change,  but  so  readily  does  it  adjust  itself,  that  new 
varieties  can  be  introduced  successfully,  provided  they  are  given 
considerable  time  to  acclimate  on  a  small  scale  before  their  pro- 
duction under  field  conditions  is  attempted. 

Wheat  has  extended  almost  over  the  earth,  except  in  extreme 
latitudes.  The  varieties  have  become  so  well  fixed  in  the  various 
regions  that  when  brought  from  long  distances  they  seldom  thrive 
at  first.  Some  strains  never  succeed,  but  others  acclimate  per- 
fectly in  new  localities.  Varieties  may  be  changed  readily  from 
spring  to  winter  sorts,  and  the  hibernating  habit  become  fixed, 
as  in  other  biennials. 

Imported  animals  are  seldom  fertile  until  acclimated.  It  is 
said,  however,  that  certain  breeds  of  the  dog  never  acclimate  in 
India  sufficiently  well  to  preserve  their  distinctive  racial  charac- 
ters. On  the  other  hand,  species  occasionally  prosper  better  in 
new  localities  than  in  old  ones.  Generally  speaking,  distance 
makes  less  difference  than  altitude,  temperature,  sunlight,  and 
food  supply.  The  evident  principle  involved  is  the  influence, 
favorable  or  otherwise,  of  certain  elements  of  climate  upon  the 
development  of  racial  characters. 

Acclimatization  to  temperatures.  It  is  a  well-known  fact  that 
if  we  bring  together  and  put  under  the  same  conditions  plants 
or  cuttings  of  the  same  species  but  grown  in  different  latitudes 
or  altitudes,  and  therefore  habitually  exposed  to  widely  different 
temperatures,  those  from  the  more  northern  localities  and  the 
higher  altitudes  will  be  the  first  to  put  out  bud  and  leaf. 

De  Candolle  of  Switzerland,  and  Bailey  of  New  York,  have 
both  conducted  extensive  experiments  in  this  direction,  and  with 
the  same  results.1 

The  former  took,  among  others,  cuttings  of  the  poplar,  the 
tulip  tree,  and  the  catalpa,  both  from  Montpellier  and  from 
Geneva,  and  planted  them  at  the  latter  place  in  glasses  of  water 
with  sand  at  the  bottom.  In  every  case  those  taken  from 
Geneva,  the  colder  locality,  leafed  out  first.  The  difference  in 
the  case  of  the  poplar  was  about  twenty-three  days,  in  the  case 
of  the  tulip  tree  about  eighteen  days,  and  in  the  case  of  the 
catalpa  twenty  days. 

1  Bailey,  Survival  of  the  Unlike,  pp.  296-301. 


TRANSMISSION   OF  MODIFICATIONS 


377 


Montpellier  is  situated  in  southern  France  on  the  Mediter- 
ranean, within  a  few  miles  of  the  coast  ;  Geneva  is  at  the  head 
of  Lake  Geneva  in  Switzerland.  The  two  points  are,  therefore, 
separated  by  about  two  and  a  half  degrees  of  latitude,  with  a 
difference  of  about  twelve  hundred  feet  in  altitude,  and  with 
some  possible  differences  in  humidity.  The  main  difference, 
however,  is  one  of  temperature  ;  and  although  both  the  tulip  tree 
and  the  catalpa  had  been  originally  introduced  from  America, 
they  had  evidently  become  so  physiologically  modified  by  their 
new  surroundings  as  to  exhibit  substantial  diversity  in  their 
reactions  to  the  same  temperatures. 

Bailey  found  that  cuttings  of  Lombardy  poplar  from  northern 
Maine  unfolded  their  buds  two  days  earlier  than  similar  cuttings 
taken  at  Ithaca.  He  placed  under  the  same  conditions  cuttings 
of  the  Concord  grape  taken  from  Maine,  New  York,  and  southern 
Louisiana,  and  found  that  they  leafed  out  in  the  order  of  their 
locality,  beginning  with  the  most  northerly.  He  reports  similar 
results  from  potatoes. 

These  were  cuttings,  and  the  experiments  show  that  the  indi- 
vidual plants  from  which  they  were  taken  had  become  thoroughly 
acclimated.  Whether  any  selection  had  been  involved  in  this 
acclimatization  we  do  not  know,  and  we  cannot  tell,  or  even  infer, 
from  these  experiments  whether  or  not  the  seeds  grown  from 
these  plants  would  have  behaved  in  the  same  way.  What  is 
shown  is  that  the  individual  plants  were  so  thoroughly  acclimated 
as  not  to  respond  in  the  same  degree  to  identical  temperature 
conditions. 

The  same  behavior  has  been  shown,  however,  with  all  seeds 
that  have  been  tried.  Bailey  found  that  corn  (maize)  grown  in 
New  York  germinated  more  readily  than  that  grown  in  South 
Carolina  or  (as  shown  by  the  following  table)  than  that  grown, 
in  Alabama  : 


FIFTH  DAY 

SIXTH  DAY 

SEVENTH  DAY 

FINAL  TOTAL 

New  York      .... 
Alabama    

14  kernels 
o  kernels 

33  kernels 
34  kernels 

2  kernels 
5  kernels 

98  per  cent 
80  per  cent 

378  TRANSMISSION 

The  corn  from  New  York  was  evidently  the  better  seed, 
because  its  final  percentage  of  germination  was  higher. 

This  fact  might  account  for  some  portion  of  the  difference  in 
promptness  of  germination,  but  we  are  informed  that  during  the 
entire  month  of  the  experiment  the  plants  from  the  northern- 
grown  seed  were  the  "  largest  and  most  vigorous  of  any."  They 
were  evidently  ahead  in  their  development.  Bailey  remarks  that 
not  only  "corn  gave  the  most  marked  results  in  favor  of  the 
northern  samples,  but  there  was  generally  a  similar  difference 
in  the  watermelons  and  beans,  with  not  one  contrary  result." 

Bonnier1  made  observations  with  Teucrium  Scorodonia  (wood 
sage)  for  eight  years.  When  grown  on  the  high  altitudes  of  the 
Pyrenees  it  produced  shorter  stems,  darker-green  and  more  hairy 
leaves,  and  more  compact  inflorescence  than  when  grown  on  lower 
land.  Seeds  gathered  from  these  plants  and  sown  in  Paris,  after 
three  years  in  the  new  habitat  "produced  elongated  stems,  with 
less  hairy  and  brighter-green  leaves,  or  plants  very  similar  to 
those  from  seeds  obtained  in  the  neighborhood  of  Paris." 

The  same  experimenter  collected  specimens  of  other  species, 
both  in  alpine  and  in  arctic  regions,  and  found  that  those  of  the 
latter  region  had  "more  rounded  cells"  and  larger  intercellular 
spaces.2 

That  races  as  well  as  individuals  acclimate  to  temperature  is 
easily  shown  and  well  known,  but  as  the  process  is  generally 
accompanied  by  selection  there  is  difficulty  in  finding  instances 
free  from  its  influence,  and  it  is  practically  impossible  to  assess 
and  deduct  its  results.  It  is  not  impossible,  however,  to  find 
cases  fairly  satisfactory. 

The  origin  and  history  of  the  Shetland  pony  is  not  known, 
and  yet  it  is  practically  certain  that  its  small  size  is  partly  the 
result  of  a  cold  climate  and  scanty  feed.  Under  these  adverse 
conditions  there  must  have  been  vigorous  natural  selection.  We 
shall  learn  in  the  chapter  on  "  Heredity  "  that  this  small  size 
could  doubtless  be  accounted  for  by  progressive  selection,  but 
the  question  here  is  whether  progressive  acclimatization  is  not 
also  involved. 

1  Vernon,  Variation  in  Animals  and  Plants,  p.  312,  from  which  the  account 
is  taken.  2  Ibid.  p.  313. 


TRANSMISSION   OF  MODIFICATIONS  379 

All  things  considered,  the  conviction  is  forced  upon  us  that 
the  Shetlands  suffered  a  progressive  diminution  because  of  low 
temperatures  or  short  feed,  or  both,  or  else  that  these  northern 
forms,  living  under  hard  conditions,  lagged  behind  their  more 
fortunate  neighbors  in  the  general  increase  in  size  that  has 
attended  the  evolution  of  the  horse  kind  generally. 

The  temperature  of  hot  springs  varies  all  the  way  from  50°  to 
98°  C.1  So  far  as  known  they  are  all  inhabited  by  living  organ- 
isms. The  protoplasm  of  ordinary  plants  and  animals  cannot  en- 
dure a  temperature  above  45°.  Death  quickly  follows  the  attempt 
to  raise  it  much  above  this  point,  and  the  nearest  relatives  of 
these  hot-springs  species  are  no  exception  to  the  general  rule. 

Yet  the  fact  remains  that  the  hot  springs  are  inhabited,  and 
by  creatures  so  small  that  their  temperature  must  be  the  same 
as  that  of  the  waters  in  which  they  live.  How  have  these  waters 
become  peopled  with  organisms  living  in  temperatures  ten  to 
fifty  degrees  higher  than  could  be  endured  by  the  stock  from 
which  they  must  have  descended  ?  2 

No  amount  of  selection  could  account  for  the  fact,  for  there 
are  no  other  known  species  living  in  an  environment  approach- 
ing these  temperatures.  There  must  have  been  progressive  de- 
velopment of  some  fashion  and  from  some  cause . 

Upon  this  point  the  experiment  of  Dallinger  is  both  signifi- 
cant and  valuable.3  He  reared  Flagellata  in  an  oven  where 
control  of  temperature  was  absolute.  Beginning  at  15.6°  C., 
he  took  four  months  in  which  to  raise  the  temperature  through 
5.5°,  a  precaution  now  known  to  be  unnecessary,  as  Flagellata 
will  endure  a  quick  rise  to  21°. 

When  the  temperature  reached  23°  the  organisms  "  began 
dying,  but  soon  ceased,  and  after  two  months  the  temperature 
was  raised  half  a  degree  more."  After  a  time  it  reached  25.5°, 
when  they  again  began  to  die,  and  for  eight  months  the  temper- 
ature could  not  be  raised  even  a  quarter  of  a  degree  above  this 

1  C.  B.  Davenport,  Experimental  Morphology,  Part  I,  pp.  250-251. 

2  The  temperature  varies  slightly  in  different  parts  of  hot  springs,  being  lower 
near  the  edge. 

3  C.  B.  Davenport,  Experimental   Morphology,  Part    I,  pp.  252-254;   Vernon, 
Variation  in  Animals  and  Plants,  pp.  379-380;  Journal  of  the  Royal  Microscopical 
Society,  VII,  191. 


38o 


TRANSMISSION 


point.  It  seemed  at  this  time  that  a  "  stationary  point "  had 
been  reached,  but  ultimately  Dallinger  was  able  to  make  slight 
additions  to  the  temperature,  and,  "proceeding  by  slow  stages " 
and  for  "several  years,"  he  succeeded  at  last  in  reaching  70°, 
when  the  experiment  was  terminated  by  an  accident. 

The  exact  length  of  time  employed  in  this  experiment  is  not 
stated,  but  it  is  supposed  by  Vernon  to  be  approximately  six 
years.  Thus  these  organisms  were  bred  for  many  generations 
during  the  experiment,  and  it  is  really  a  case  of  race  acclimati- 
zation. The  organisms  were  monads,  it  is  true,  which  multiply 
by  fission,  so  that,  as  Davenport  states,  "  the  high  temperatures 
acted  upon  the  same  protoplasm  at  the  end  of  the  experiment 
as  at  the  beginning."  Is  there  any  reasonable  doubt  that  this 
is  the  process  by  which  organisms  of  this  character  have  gained 
access  to  our  hot  springs  even  under  natural  conditions  ? 

In  this  experiment  three  points  are  noteworthy  : 

1.  There  were  certain  "sticking  points,"  so  to  speak,  that 
were  difficult  to  get  over,  but  after  these  were  passed,  additional 
increase  of  heat  was  easily  endured.    The  temperature  of  25.5° 
was  one  of  these  sticking  points. 

2.  It  was  found  that  the  process  of  acclimatization  did  not 
become  gradually  slower  and  more  difficult  with  the  higher  tem- 
peratures, for  25.5°  was  the  most  difficult  temperature  encoun- 
tered, requiring  eight  months  to  surmount,  while  the  rise  from 
41.7°  to  58.3°  was  made  in  seven  months,  and  that  from  61.1° 
to  70°  in  a  few  months  (number  not  stated),1  showing  that  the 
limits  of  variability  were  not  reached,  and  suggesting  that  the 
experiment  might  have  been  continued  much  longer  and  the  in- 
crease pushed  much  farther. 

3.  Organisms  acclimated  to  70°  died  off  when  returned  to  the 
original  temperature  of  15.6°,  showing  that  the  modification  of 
the  protoplasm  was  not  only  profound  but  also  permanent.    In 
other  words,  here  is   a   species   whose   temperature   has   been 
raised  through  so  many  degrees,  and  its  protoplasm  so  altered, 
that  it  can  no  longer  endure  its  original  normal  temperature. 
It  has  been  taken  entirely  out  of  its  field  and  placed  in  another 
so  far  removed  as  to  have  no  connection  with  its  former  state. 

1  Vernon,  Variation  in  Animals  and  Plants,  p.  380. 


TRANSMISSION   OF  MODIFICATIONS  381 

It  is  true  there  were  deaths  during  this  process,  but  the 
selection  was  insignificant,  and  the  conviction  is  absolute  that 
the  result  was  in  no  large  sense  due  to  the  selective  process. 

In  the  opinion  of  the  writer  this  is  proof  absolute  of  one  of 
three  things  : 

1.  Either  the  direct  transmission  of  modifications,  —  a  thing 
not  difficult  to  imagine  considering  the  mild  sort  of  transmission 
involved  in  reproduction  by  fission ; 

2.  The  direct  action  of  the  temperature  upon  the  constitu- 
tion of  the  protoplasmic  basis  of  life,  —  a  contingency  not  spe- 
cially applicable  in  this  case,  where  the  germ   undergoes  but 
slight   development   and   there   is   no   practical   distinction   be- 
tween germ  plasm  and  body  plasm ; 

3.  Or,  if  of  neither  of  these,  then  it  is  proof  of  what  may 
be  called  progressive  variation,  in  which,  with  a  species  living 
under  changing  conditions,  new  centers  of  variability  are  being 
constantly  established. 

The  significant  point  is  that  in  this  instance  the  deviations 
are  due  not  to  selection  but  to  the  direct  action  of  the  environ- 
ment, and  we  are  left  to  explain  cases  of  this  kind  by  assuming 
either  that  the  modifications  are  themselves  directly  transmitted, 
or  else  that  the  external  conditions  have  influenced  the  germ  as 
well  as  the  body. 

This  is  not  difficult  to  believe  of  such  all-pervasive  influences 
as  temperature,  and  it  may  well  be  that  certain  outside  influences 
can  make  themselves  felt  in  this  way  when  others  which,  from 
their  nature,  may  affect  the  development  but  cannot  reach  the 
germ,  will  not  make  themselves  permanently  felt  except  through 
individual  adaptation  and  selection. 

Acclimatization  to  poisons.  That  individuals  acquire  a  high 
resistance  to  poisons  has  already  been  shown.  Speaking  gener- 
ally, living  protoplasm  will  soon  adjust  itself  to  any  chemical 
influence  not  fatal  or  so  extremely  injurious  as  to  overcome  its 
powers  of  adaptability.  Physicians  change  remedies  frequently 
for  the  reason  that  they  soon  lose  their  characteristic  action. 

The  acquired  resistance  of  man  to  arsenic  and  other  poisons, 
of  mice  to  ricin,  of  the  horse  to  the  filtrate  of  the  diphtheria 
bacillus,  of  the  rabbit  to  that  of  hydrophobia,  and  of  animals 


782  TRANSMISSION 

«j 

in  general  to  poisons  of  all  sorts  gradually  administered,  is 
well  known.1 

So  far  as  we  are  able  to  judge,  immunity  to  infectious  diseases 
is  produced  in  the  same  way.  One  attack  of  certain  diseases 
serves  to  render  the  individual  immune  through  life.  The 
question  that  interests  us  at  this  point  is  this  :  Is  this  immunity 
in  any  sense,  or  to  any  degree,  transmitted  to  the  descendants  f 

It  is  claimed  by  some  that  if  a  sow  recovers  from  a  case  of 
hog  cholera  suffered  while  carrying  young,  the  pigs  will  be  born 
with  a  high  degree  of  resistance,  if  not  absolute  immunity ;  the 
idea  being  that  they  acquired  in  utero  from  the  blood  serum  of 
the  mother  the  same  kind  of  immunity  that  could  be  produced 
by  inoculation. 

There  is  too  little  experimental  evidence  as  yet,  and  we  know 
too  little  of  the  real  nature  of  acclimatization,  to  warrant  positive 
conclusions.  What  is  known,  however,  is  sufficient  to  raise  some 
interesting  and  exceedingly  suggestive  questions. 

If  immunity  can  be  produced  in  the  mother  by  the  repeated 
injection  of  the  chemical  products  of  disease,  and  if  such  im- 
munity be  permanent,  then  why  should  not  the  young,  whose 
blood  serum  is  derived  from  the  mother,  be  also  of  the  same 
character?  Whence  come  our  "  natural  immunes  "  ?  are  they 
mutants,  or  are  they  the  products  of  immunizing  influences 
from  the  parentage  ?  Recent  investigations  seem  to  indicate 
specific  qualities  in  blood  serum,2  and  it  may  very  well  be 
that  "  blood  relationship  "  means  more  than  we  have  hitherto 
supposed. 

To  what  extent  immunity  is  purely  a  chemical  question,  and 
to  what  extent  it  is  connected  with  the  power  of  the  white 
corpuscles  to  attack  and  digest  invading  organisms,  we  do  not 
know.  In  so  far  as  it  depends  upon  or  affects  the  serum  of  the 
blood  it  may  well  be  a  transmissible  quality  from  the  female 
mammal  if  not  from  other  parents. 

1  C.   B.   Davenport,   Experimental   Morphology,   Part   I,   pp.   28-32 ;  Vernon. 
Variation  in  Animals  and  Plants,  pp.  386-387. 

2  When  the  blood  serum  of  one  species  is  injected  into  the  veins  of  another, 
the  most  injurious  effects  are  said  often  to  follow,  and  the  so-called  precipitin 
test  seems  to  establish  the  fact  that  differences  in  blood  serum  of  different  species 
are  profound.    See  Blood  Immunity  and  Blood  Relationship,  by  Nuttall,  reviewed 
in  Science,  October  28,  1904. 


TRANSMISSION   OF   MODIFICATIONS  38-3 

Chemical  action  of  normal  secretions.  In  the  opinion  of  the 
writer,  those  who  discuss  the  subject  of  the  transmission  of 
modifications  (acquired  characters)  as  if  it  were  a  single  issue, 
and  dismiss  it  in  toto  as  impossible  upon  the  theoretical  ground 
that  no  such  modifications  could  by  any  manner  of  means  affect 
the  germ  plasm  —  those  who  discuss  and  dismiss  the  matter  in 
this  manner  commit  a  fundamental  error  in  overlooking  the 
fact  that,  as  a  whole,  this  is  a  broad  question,  or  rather  a  series 
of  questions,  and  that  the  living  organisms,  exposed  as  they 
are  for  generations  to  outside  conditions  absolutely  essential  to 
their  existence,  present  many  points  of  contact  in  which  they 
are  exceedingly  susceptible  to  influence.  They  make  the  fatal 
error,  too,  of  failing  to  distinguish  between  those  circumstances 
that  affect  only  the  externals  of  the  body  and  those  all-pervading 
influences  that  affect  the  very  constitution  of  the  organism. 

For  example,  it  is  now  well  known  that  the  perfect  working 
of  the  body  as  a  whole  depends  upon  the  presence  of  specific 
secretions  of  certain  organs,  many  of  which  were  once  thought 
to  be  functionless.  Destruction  of  the  thyroid  gland  at  once 
arrests  not  only  the  physical  but  the  mental  development.  In 
children  its  degeneration  results  in  retarded  mental  development 
and  even  in  idiocy,  a  calamity  that  can  be  ameliorated,  and  even 
averted,  by  the  injection  of  thyroid  substance  of  animals.  Bau- 
mann  found  that  the  secretions  of  this  gland  are  characterized  by 
the  presence  of  iodin,  which  is  found  nowhere  else  in  the  body.1 

On  this  same  general  question  Vernon,  after  speaking  of  the 
frequently  fatal  effect  of  removing  the  thyroid  gland,  unless  the 
animal  be  fed  thyroid  substance,  remarks  as  follows  : 2 

Extirpation  of  the  suprarenal  glands  results  in  much  more  speedy  death, 
and  here  again  the  injection  of  extracts  may  delay  the  fatal  issue.  Extir- 
pation of  the  pancreas  causes  the  production  of  severe  diabetes,  and  ulti- 
mately death,  but  such  an  effect  may  be  avoided  by  the  grafting  of  a 
portion  of  excised  gland  in  the  peritoneal  cavity  or  the  tissues.  .  .  .  Again, 
extirpation  of  the  total  kidney  substance  of  the  dog  leads,  not  to  a  dimin- 
ished secretion  of  urine,  but  to  a  largely  increased  secretion,  accompanied 
by  a  rapid  wasting  away,  which  soon  ends  fatally.  Hence  the  kidneys  may 
possess  an  influence  on  the  metabolism  of  the  whole  body,  as  well  as  their 

1  Loeb,   Physiology  of  the  Brain,  pp.   207-208.    Extracts  of  this  and  other 
glands  are  now  regularly  prepared  at  our  larger  slaughterhouses. 

2  Vernon,  Variation  in  Animals  and  Plants,  pp.  358-360. 


384  TRANSMISSION 

obvious  secretory  function.  The  spleen  appears  to  have  an  internal  secre- 
tion which  is  of  influence  in  setting  free  the  pancreatic  ferment.  Finally, 
extracts  of  various  nervous  tissues  —  brain,  spinal  cord,  and  sciatic  nerve  — 
have  been  found,  when  intravenously  injected,  to  produce  a  distinct  fall  of 
blood  pressure,1  whilst  those  of  the  pituitary  body  produce  a  marked  rise. 

Here  is  a  basis  for  possible  transmission  of  such  diseases  as 
might  be  connected  with  normal  secretions,  as  it  certainly  is  for 
any  external  influence  that  could  permanently  affect  either  their 
character  or  their  quantity.  This  opens  a  wide  field  for  the  pos- 
sible and  permanent  influence  of  causes  of  variation  lying  origi- 
nally outside  the  germ,  but  whose  effects  are  of  such  a  nature 
as  to  make  themselves  felt  throughout  the  entire  organism,  and 
to  influence  not  only  its  development  and  activity  but  its  power 
of  transmission  as  well. 

Akin  to  this  is  the  possible  effect  of  such  chemicals  as  alco- 
hol, which  has  specific  relations  to  protoplasm  and  is  one  of 
those  influences  that  apparently  are  capable  of  penetrating  to 
the  uttermost  limits  of  the  organism.  Without  doubt  other  mate- 
rial elements  of  food  and  drink  exert  fundamental  influences 
of  a  chemical  nature,  whose  effects  may  reach  the  germinal  mat- 
ter and  thus  of  necessity  descend  from  generation  to  generation, 
to  the  distinct  modification  of  the  race. 

How  races  acclimate.  How  do  races  become  acclimated  ? 
There  are  at  least  five  methods  competent  to  explain  the 
process  : 

1.  The  acclimatization  of  all  the  individuals  of  a  race,  each 
one  in  the  successive  generations  separately ; 

2.  Selection,  obliterating   such  individuals  as  are   unable  to 
acclimate  successfully,  thus  restricting  descent  to  the  fittest ; 

3.  The  direct  transmission  of  individual  modifications  (ac- 
quired characters),  at  least  in  some  slight  degree,  the  accumula- 
tion of  which,  ultimately  produces  complete  acclimatization  in 
the  race ; 

4.  It  is  possible  that  the  same  causes  which  induce  modifica- 
tions in  the  individuals  may  also  exert  influences  so  deep-seated 
as  to  affect  the  germ  plasm  directly  and  in  this  way  produce  all 
the  appearances  of  inheritance  of  modification  ; 

1  Due  probably  to  specific  action  on  the  heart. 


TRANSMISSION   OF   MODIFICATIONS  385 

5.   The  process  may  be  explained  by  the  old  principle  of  pro 
gressive  variation. 

Of  these,  the  first  two  are  certainly  always  at  work.  Mani- 
festly all  the  individuals  of  succeeding  generations,  or  most  of 
them  at  least,  will  spontaneously  acclimate  to  the  changed  con- 
dition. This  of  itself  would  give  an  appearance  of  race  acclimati- 
zation, even  though  no  change  had  been  wrought  in  its  inherited 
nature.  If,  now,  to  this  is  added  the  effect  of  selection,  we  at 
once  recognize  a  powerful  cause  of  real  race  acclimatization. 
Nor  does  this  necessitate  the  destruction  of  any  very  large 
numbers.  If  only  their  life  period  be  shortened  or  their  fer- 
tility decreased,  their  relative  importance  in  the  race  would  be 
greatly  lessened  thereby  and  the  effect  of  selection  felt. 

Either  one  of  these  two  processes  alone  is  entirely  competent 
to  account  for  the  full  appearance  of  acclimatization.  Doubtless 
both  are  always  present  and  at  work  jointly,  but  this  does  not 
preclude  the  possibility  of  other  agencies  also.  The  fifth  possi- 
bility depends  upon  selection  for  its  efficiency. 

The  chief  objection  to  relying  upon  selection  to  fully  account 
for  race  acclimatization  is  that  the  destruction  is  frequently  too 
slight,  and  the  race  response  too  prompt ;  yet  it  is  not  sufficiently 
prompt  and  instantly  complete  to  account  for  the  phenomena  by 
the  successive  acclimatization  of  all  individuals  separately. 

There  is  a  rapidly  cumulative  element  somewhere.  The  whole 
movement  is  too  rapid  for  selection,  especially  with  the  exceed- 
ingly moderate  destruction  of  individuals  that  sometimes  takes 
place.  Plants  do  not  acclimate  by  reason  of  most  of  them  being 
killed  off,  yet  there  is  a  strongly  progressive  element  involved. 
The  inevitable  conclusion  is,  in  the  opinion  of  the  writer,  that 
the  chief  effects  of  acclimatization  are  transmitted. 

Whether  this  transmission  be  direct  or  indirect ;  whether  it 
be.  due  to  the  peculiar  development  of  the  individual  impressing 
itself  upon  the  germ,  or  to  climatic  influences,  like  tempera- 
ture, food,  etc.,  which  being  all-pervading,  affect  the  general 
state  of  life  and  influence  the  germ  direct,  is  another  and  more 
important  matter. 

That  the  simple  removal  of  a  part  does  not  affect  transmis- 
sion is  significant.  The  old  contention  that  the  protoplasm  of 


386  TRANSMISSION 

the  germ  and  the  protoplasm  of  the  developed  body  are  essentially 
different  has  long  since  been  disproved.  Both  are  susceptible 
to  any  influence  that  can  reach  them,  and  in  climatic  conditions 
generally  we  have  abundant  influences  of  this  kind. 

May  we  not  consider  as  established  the  possibility  that  the 
germ  itself,  and  therefore  descent,  may  be  directly  modified  by 
external  influences  ?  How  far  this  may  go,  and  what  influences 
are  included,  is  another  subject,  and  one  calling  for  the  most 
careful  study  and  requiring  the  most  reliable  data  as  a  basis  for 
an  intelligent  opinion. 

The  present  state  of  knowledge  is  insufficient  to  entirely 
solve  the  problem,  but  there  is  additional  evidence  worth 
consideration. 

SECTION    VI  — EVIDENCE    FROM    HABIT   AND    INSTINCT. 
IS  INSTINCT   INHERITED   HABIT? 

Habit  and  instinct  both  refer  to  the  use  which  individuals 
make  of  those  racial  characters  that  are  capable  of  action.  It 
is  a  matter  of  common  knowledge  that  an  oft-repeated  act 
speedily  becomes  a  habit  with  the  individual,  and,  as  such, 
repeats  itself  almost  mechanically ;  so  that  what  was  at  first 
a  nice  adaptation  of  means  to  end  shortly  becomes  little  more 
than  reflex  action. 

Building  upon  this  fact,  it  is  a  plausible  assumption  that 
what  is  habit  with  one  generation  becomes  instinct  in  the  next. 
It  is  a  sweeping  but  easy  generalization  that  "  no  distinct  line 
can  be  drawn  between  instinct  and  reason  "  ; 1  that  instinct  is 
inherited  habit,  and  reason  inherited  instinct  modified  by  indi- 
vidual experience. 

This  is  the  position  taken  by  many  of  the  older  naturalists, 
especially  Romanes,  who  defined  instinct  as  "  reflex  action  into 
which  there  is  imported  the  element  of  consciousness," 2  and 
reason  as  "  the  faculty  which  is  concerned  with  the  intentional 
adaptation  of  means  to  end."  2 

1  Romanes,  Animal  Intelligence,  p.  15. 

2  Ibid.  p.  17.    This  volume  is  perhaps  the  most  extreme  exponent  of  the  idea 
of  inherited  habit,  and  of  intelligence  as  lying  at  the  basis  of  all  animal  activity. 


TRANSMISSION   OF   MODIFICATIONS  387 

Thus  the  whole  question  is  up  again  in  this  connection.  Will 
the  habit  of  the  individual  be  transmitted  to  its  offspring  ?  Is 
the  habit  of  one  generation  the  instinct  of  the  next  ?  If  so,  then 
we  have  a  case  of  transmission  of  modifications  (inheritance  of 
acquired  characters)  of  the  most  direct  and  certain  kind. 

The  answer  to  the  question  is  important  for  its  own  sake,  but 
more  especially  for  the  light  it  may  throw  upon  the  main  ques- 
tion now  in  hand.  To  arrive  at  a  safe  answer  it  is  necessary  to 
give  more  than  a  passing  notice  to  the  nature  of  instinctive  acts, 
and  to  critically  determine  whether  instinct  is  built  upon  habit 
or  habit  upon  instinct. 

Nature  of  instinctive  acts.  Most  acts  of  intelligent  beings 
are  performed  for  a  particular  purpose  and  for  definite  ends. 
Most  such  acts  are  controlled  by  a  greater  or  less  degree  of 
purposeful  adaptation  of  means  to  end  that  involves  knowledge 
of  results,  based  on  experience  and  merging  naturally  into  habit. 
Habit  is  then  the  customary  use  to  which  the  individual  puts  the 
parts  with  which  it  is  endowed  by  nature,  after  they  have  reached 
full  development.  Its  chief  interest  to  us  at  this  point  arises 
from  the  fact  that  another  individual  might  put  the  same  parts 
to  a  different  use,  while  in  instinctive  acts  use  is  a  function  of 
structure,  and  but  one  set  of  actions  is  possible  except  under 
greatly  changed  conditions. 

The  term  "  instinctive  "  is  applied  to  those  acts  which  are  per- 
formed without  previous  experience  and  perhaps  under  circum- 
stances that  preclude  all  knowledge  of  what  the  result  will  be  ; 
so  that,  as  far  as  the  individual  is  concerned,  there  is,  and  can  be, 
no  consciousness  of  purposeful  action  or  of  adaptation  of  means 
to  end,  and  yet  the  action,  often  complicated  in  the  extreme, 
may  be  eminently  adaptive  and  exhibit  every  appearance  of  being 
the  act  of  a  most  intelligent  being.  Young  mammals  suck  with 
the  lips  ;  young  waterfowls  swim  and  dive,  but  land  birds  do  not ; 
young  squirrels  hide  objects,  and  even  in  a  room  go  through  the 
motions  of  digging  and  burying ;  young  chicks  have  their  own 
peculiar  cry,  and  peck  at  shining  objects ;  birds  build  their  nests 
without  instruction  or  assistance  from  older  or  more  experienced 
individuals.  These  are  instinctive  acts  of  the  simplest  order ; 
many  others,  however,  are  extremely  complicated.  For  example, 


388  TRANSMISSION 

an  insect  burrows  a  cavity  and  lays  its  egg.  It  then  attacks 
another  insect,  stings  it  so  as  to  paralyze  but  not  to  kill  it,  drags 
it  to  the  burrow,  tucks  it  in  next  to  the  egg  where  it  will  serve 
as  food  to  the  larva,  seals  all  up,  and  goes  away. 

The  yucca  moth  emerges  from  the  cocoon  just  as  the  yucca 
opens  its  flowers,  each  for  a  single  night.  The  female  collects 
pollen  from  one  flower  and  kneads  it  into  a  bundle.  She  then 
flies  to  another,  makes  a  puncture,  and  lays  her  egg  among  the 
ovules,  after  which  she  darts  to  the  stigma  and  "  stuffs  the 
pollen  pellet  into  the  funnel-shaped  opening."  V  It  is  supposed 
that  this  is  the  only  way  in  which  the  insect  reproduces,  and  the 
chief  way  in  which  the  yucca  is  fertilized. 

Here  definite  and  important  ends  are  dependent  not  only 
upon  complicated  acts  but  also  upon  the  serial  order  of  their  per- 
formance, —  all  without  previous  knowledge  or  experience  on  the 
part  of  the  agent,  for  the  female  in  most  cases  is  performing 
this  act  for  the  first  time,  and  in  many  cases  will  not  live  till  the 
eggs  hatch.  Given  any  amount  of  intelligence,  therefore,  she 
could  not  know  the  final  result  of  her  own  industry,  although 
the  entire  process  has  every  appearance  of  intelligent,  even  delib- 
erate, action.  It  is  noticeable  at  once  that  instincts  of  this  sort 
are  concerned  with  those  acts  which,  like  reproduction,  are  funda- 
mental to  race  preservation. 

Is  instinct  founded  on  habit  ?  The  outcome  of  most  instinc- 
tive acts  is  so  clearly  the  preservation  of  life  and  the  good  of 
the  species,  the  acts  themselves  are  often  so  extremely  compli- 
cated, their  separate  steps  are  so  nicely  adjusted  to  the  final 
end,  their  proper  serial  order  is  so  accurately  observed,  the 
appearance  of  deliberate,  purposeful  action  is  so  genuine,  the 
need  of  intelligent  direction  at  some  period  of  the  organization  of 
the  series  is  so  apparent,  the  importance  of  the  ends  achieved  is 
so  obvious,  and  the  similarity  between  the  instinct  of  a  race  and 
the  habit  of  an  individual  is  so  close  that  many  naturalists  have 
leaped  to  the  conclusion  that  instinct  is  inherited  habit ;  in  other 
words,  that  what  has  been  found  beneficial  in  the  experience  of 
individuals  has  become  habitual  with  them,  and  through  their 
descendants  it  has  become  the  habit  of  the  race.  This  position 

1  A  free  transcript  from  Morgan,  Habit  and  Instinct,  p.  14. 


TRANSMISSION   OF  MODIFICATIONS  389 

was  quite  generally  taken  by  the  older  naturalists.  As  Romanes 
puts  it,1  "  Instinctive  actions  are  actions  which,  owing  to  their 
frequent  repetition,  become  so  habitual  in  the  course  of  genera- 
tions that  all  the  individuals  of  the  same  species  automatically 
perform  the  same  actions  under  the  stimulus  applied  by  the 
same  appropriate  circumstances."  He  adds  :  "  Rationaf  actions, 
on  the  other  hand,  are  actions  which  are  required  to  meet  cir- 
cumstances of  comparatively  rare  occurrence  in  the  life  history 
of  the  species,  and  which,  therefore,  can  be  performed  only  by 
an  intentional  effort  of  adaptation." 

If,  now,  instinct  be  inherited  habit,  and  reason  only  modified 
instinct,  then  we  have  an  unbroken  chain,  from  the  -simplest 
adaptive  act  up  to  the  highest  mental  generalization,  —  all  the 
product  of  inherited  experience.  This  is  inheritance  of  indi- 
vidual modifications  (acquired  characters)  of  the  most  pronounced 
type,  and  if  true,  it  affords  the  most  important  evidence  upon  the 
question  now  under  consideration. 

A  critical  analysis  of  the  matter  makes  clear  the  fact  that  this 
conclusion  involves  the  following  extreme  assumptions,  whose 
correctness  must  be  carefully  considered  and  not  accepted  with- 
out question,  as  is  too  often  done  : 2 

1.  That  instinctive  acts  are  performed  perfectly  at  the  first 
attempt,  —  the  traditional  "  unerring  instinct." 

2.  That  they  are  carried  out  substantially  in  the  same  way  by 
all  individuals  of  the  race  and  by  the  same  individual  in  succes- 
sive performances.3 

3.  That  instinctive   acts  are  always  adaptive,  thus  showing 
their  ultimate  origin  in  purposeful  acts.4 

4.  That  habit  precedes  instinct,   and  that  instinct  finds  its 
directive  force  in  inherited  experience.5 

It  is  well  to  consider  these  points  somewhat  carefully. 

Instinct  not  unerring.  The  earliest  instinct  of  the  young 
mammal  is  to  suck.  Moreover,  it  is  an  instinct  connected  with 
the  preservation  of  life ;  yet  the  calf  will  be  entirely  satisfied 

1  Romanes,  Animal  Intelligence,  pp.  16-17. 

2  Read,   in   this  general  connection,    Habit   and   Instinct,  by  Lloyd  Morgan, 
especially  pp.  29-127. 

3  Romanes,  Animal  Intelligence,  p.  17.          4  Ibid,  p,  15.          6  Ibid.  pp.  16-17. 


390  TRANSMISSION 

with  its  neighbor's  ear,  the  baby  with  its  own  fist,  or  the  young 
lamb  with  a  lock  of  wool,  which,  if  the  mother  be  young  and 
inexperienced,  it  may  suck  until  it  starves.  Young  chicks  will 
pick  up  and  swallow  at  first  whatever  attracts  their  attention, 
—  bits  of  colored  yarn,  or  "nasty"  caterpillars,  as  readily  as 
"  good  "  worms  ;  but  they  rapidly  learn  by  experience.1 

The  instinct  of  the  young  chick  is  to  strike  at  any  small 
object  that  attracts  its  attention  either  by  its  color  or  its  move- 
ments ;  yet  the  first  attempts  are  extremely  awkward  and  sel- 
dom result  in  a  catch,  the  bill  going  some  distance  to  one  side 
of  the  object.  Gradually,  however,  it  learns  by  experience  to 
strike  accurately.2 

Walking,  flying,  swimming,  and  talking  are  instinctive  acts 
with  species  possessing  the  requisite  mechanism;  yet  the  first 
attempts  are  exceedingly  crude,  and  much  experience  and  prac- 
tice are  required  before  effective  proficiency  is  developed. 

A  fair  study  of  the  subject  can  but  convince  the  student  that 
instinct  is  at  first  but  little  more  than  an  impulse  to  action  in 
general,  which,  however,  rapidly  shapes  up  into  well-ordered 
performance  under  the  corrective  influence  of  experience. 

Instinctive  acts  are  not  performed  in  the  same  way  either  by 
all  individuals  or  by  the  same  individual  at  successive  perform- 
ances. To  watch  the  complicated  acts  of  the  egg-laying  instinct 
in  many  insects  is  at  first  to  become  convinced  that  this  marvel- 
ous sequence  of  events  is  assured  only  by  the  highest  intelli- 
gence or  by  an  instinct  that  is  unerring  in  its  directive  power ; 
yet  a  little  further  study  will  convince  the  student  that  these 
complicated  instinctive  acts  are  not  always  carried  forward  on 
the  typical  plan,  nor  are  they  always  successfully  executed.  On 
the  contrary,  important,  ev^n  significant,  steps  are  often  omitted 
from  the  series,  and  different  individuals  differ  greatly  in  the 
degree  of  thoroughness  and  the  rapidity  with  which  the  work  is 
carried  forward. 

For  example,  Crandall  endeavored  to  note  accurately  all  the 
steps  in  the  process  of  making  the  puncture  and  laying  the  egg 
of  the  plum  curculio  working  upon  the  apple.3 

1  Morgan,  Habit  and  Instinct,  pp.  40-44,  50.  2  Ibid.  pp.  37,  47. 

3  Bulletin  No.  98,  Illinois  Experiment  Station,  pp.  500-504. 


TRANSMISSION   OF  MODIFICATIONS  391 

Of  many  attempts  to  watch  and  record  the  process  from 
first  to  last,  only  three  were  successful  in  covering  the  entire 
period.  The  rest  were  fragmentary,  covering  only  portions  of 
the  process.  This  was  owing  to  the  difficulty  of  keeping  the 
insect  under  focus  for  the  fifteen  to  twenty-five  minutes  re- 
quired for  the  complete  operation  without  disturbing  its  work. 
The  record  of  the  observer  is  as  follows  : 

In  the  first  observation  the  female  moved  about  the  apple  for  several 
seconds,  keeping  the  end  of  her  beak  in  contact  with  the  surface,  as  if 
seeking  a  favorable  spot.  When  the  exact  spot  was  decided  upon",  the 
minute  jaws  at  the  end  of  the  snout  began  a  rapid  movement  which  quickly 
made  an  opening  through  the  skin.  This  opening  was  no  larger  than  neces- 
sary for  admission  of  the  tip  of  the  beak.  No  skin  was  removed ;  it  was 
simply  torn  and  thrust  aside  to  give  access  to  the  pulp  below.  Later,  as 
the  excavation  proceeded,  the  broken  skin  was  seen  as  a  sort  of  fringe 
around  the  beak  at  the  surface  of  the  fruit.  As  soon  as  excavation  in  the 
pulp  was  commenced,  the  beak  was  deflected  backward  so  that  the  work 
was  carried  on  under  the  insect,  just  beneath  the  skin  and  nearly  parallel 
with  the  surface.  As  the  work  advanced,  the  opening  through  the  skin 
became  slightly  enlarged  by  lateral  motions  of  the  beak.  The  pulp  was 
all  eaten  as  excavated.  During  the  process  the  beak  was  not  once  with- 
drawn, nor  was  there  any  cessation  of  motion.  When  the  excavation  of 
the  cavity  was  completed  the  beak  was  withdrawn  by  a  quick  motion,  the 
insect  turned  about,  adjusted  the  tip  of  the  abdomen  to  the  opening  and 
deposited  an  egg,  which  was  forced  to  the  extremity  of  the  excavation  by 
the  ovipositor.  The  insect  now  rested  without  motion  for  two  minutes ; 
then,  turning  again,  proceeded  to  cut  the  crescent  in  front  of  the  egg. 
This  crescent  puncture  was  not  wholly  a  separate  puncture,  but,  starting  in 
the  original  opening  through  the  skin,  was  cut  laterally  in  either  direction, 
partly  by  the  jaws  and  partly  by  crowding  the  beak  first  one  way  and  then 
the  other.  The  direction  of  the  beak  was  but  little  deflected  from  the  per- 
pendicular, and  the  cut  was  made  as  deep  as  the  length  of  the  beak  would 
allow.  The  pulp  torn  away  in  making  the  crescent  was  eaten,  just  as  was 
done  in  excavating  the  egg  cavity.  The  crescent  completed,  the  insect 
walked  away,  drew  the  legs  closely  under  the  body,  and  settled  down, 
apparently  to  sleep.  The  time  occupied  in  the  process  described  was  dis- 
tributed-as  follows : 

Excavating  egg  cavity    .     .     .'    .     .     .     .  9    minutes 

Deposition  of  egg      .     .     .     .     .     .     .     .  i    minute 

Rest 2    minutes 

Cutting  the  crescent       3}  minutes 

Total 15'-  minutes 


392  TRANSMISSION 

The  egg  cavity  was  cylindrical,  with  a  rounded  bottom,  and  by  measure- 
ment was  found  to  be  0.04  inch  in  depth.  The  egg  when  deposited  very 
nearly  filled  the  cavity. 

The  second  observation  of  the  complete  process  was  nearly  identical 
with  the  one  described.  The  insect  spent  no  time  in  choosing  the  exact 
spot,  but  went  to  work  at  once.  It  worked  in  a  more  leisurely  way  and  did 
not  excavate  as  deep  an  egg  cavity.  Eleven  minutes  were  spent  on  the 
cavity,  two  minutes  in  depositing  the  egg,  two  in  rest,  and  four  in  cutting 
the  crescent,  —  a  total  of  nineteen  minutes.  The  egg  cavity  measured  0.035 
inch  in  depth  and  was  completely  filled  by  the  egg.  On  completion  of  the 
process  the  insect  moved  a  short  distance  and  immediately  began  a  second 
cavity. 

Essential  differences  from  procedure  in  the  two  preceding  cases  were 
noted  in  the  third  complete  observation.  Excavation  of  the  egg  cavity  was 
the  same,  except  that  it  was  deeper  in  the  pulp  and  of  greater  extent.  After 
depositing  the  egg  the  beetle  turned,  and  with  her  beak  worked  the  egg 
back  to  the  bottom  of  the  cavity.  Then  she  began  tearing  off  bits  of  skin 
and  pulp,  which  were  carefully  packed  in,  above  the  egg,  tmtil  the  cavity  was 
full.1  Following  this,  the  crescent  was  cut  in  much  the  same  manner  as  in 
the  preceding  cases.  Then  she  appeared  to  make  a  final  inspection,  and 
added  some  further  packing  above  the  egg.  Finally  the  work  appeared  to 
be  satisfactory  and  she  walked  away  and  began  a  second  puncture.  The 
time  consumed  in  this  process  was  longer  than  in  the  others,  and  was  divided 
as  follows : 

Excavating  egg  cavity    .     .     .     .     .     .     .12    minutes 

Depositing  egg i^  minutes 

Placing  the  egg  with  the  beak     ....     2    minutes 

Packing  the  cavity 4    minutes 

Cutting  the  crescent 4    minutes 

Finishing  touches 3    minutes 

Total 26^  minutes 

Among  the  many  cases  where  only  part  of  the  process  was  observed 
some  anomalies  were  noted.  In  two  cases  the  insect  walked  away  im- 
mediately after  depositing  the  egg  and  made  no  crescent  cut.  In  three 
cases  beetles  were  seen  to  cut  crescents  and,  moving  a  short  distance, 
begin  other  punctures.  These  crescents  had  no  egg  cavities  and  no  eggs 
were  deposited  in  them.  In  two  cases  eggs  were  found  deposited  directly 
in  crescent  cuts,  neither  of  which  had  the  usual  egg  cavity.  Marked  varia- 
tion in  depth  of  the  egg  cavity  was  frequently  observed.  Not  infrequently 
the  cavity  is  so  shallow  that  the  tip  of  the  egg  protrudes,  and  sometimes 
its  depth  is  nearly  equal  to  twice  the  length  of  the  egg.  Packing  the  egg 
cavity  with  pieces  of  pulp  is  a  common,  but  not  universal,  practice;  often 
this  is  neglected,  even  where  the  cavity  is  deep.  .  .  . 

1  Italics  are  mine. 


TRANSMISSION   OF  MODIFICATIONS  393 

When  reading  of  the  various  processes  and  acts  in  insect  economy,  as 
observed  and  recorded  in  published  life  histories,  it  is  quite  natural  to 
suppose  that  these  processes  are  fixed,  absolute,  and  unchangeable,  while 
as  matter  of  fact  many  of  them  are  subject  to  modifications.  Sometimes 
these  variations  have  apparent  reason  in  surrounding  conditions,  and  again 
they  can  be  ascribed  only  to  individual  peculiarity.  .  .  . 

A  crescent  puncture  is  usually  supposed  to  represent  an  egg  or  an 
attempt  at  egg  laying,  but  this  does  not  always  hold  true,  because,  as 
stated  above,  some  crescent  cuts  are  made  without  the  accompaniment  of 
egg  laying.  On  May  27,  1903,  fallen  apples,  twenty-five  in  number,  were 
picked  up  at  random  for  examination  of  the  crescent  punctures.  Nearly 
all  were  more  or  less  punctured  by  the  apple  curculio,  but  these  punctures 
are  not  considered  here.  Two  fruits  bore  apple-curculio  punctures  only,  so 
that  the  number  examined  for  crescent  marks  was  twenty-three.  On  these 
twenty- three  apples  were  fifty-eight  crescent  marks,  or  2.52  to  each  apple. 
There  were  also  thirty-five  feeding  punctures  made  by  the  plum  curculio. 
Of  the  fifty-eight  crescent  cuts,  fourteen,  or  24.14  per  cent,  had  no  egg 
cavities  and  contained  no  eggs.  The  remaining  forty-four  crescent  cuts 
had  forty-five  egg  cavities.  Some  variation  in  the  location  of  the  egg 
cavities  was  observed  ;  usually  they  occupied  the  center  of  the  crescent, 
but  some  of  these  were  not  so  situated.  Of  the  forty-five  egg  cavities, 
thirty-four,  or  75.56  per  cent,  were  located  at  or  near  the  center  of  the 
crescent ;  eleven,  or  24.44  Per  cent,  were  located  near  the  ends  of  the 
crescents.  In  one  case  there  were  two  egg  cavities  within  one  crescent, 
one  on  each  side  halfway  between  the  center  and  tip.  By  another  modifi- 
cation one  of  the  egg  cavities,  instead  of  .being  excavated  from  the  surface, 
was  excavated  from  the  bottom  at  the  center  of  a  crescent  cut.  It  was  of 
usual  dimensions,  extended  back  obliquely  towards  the  surface,  and  con- 
tained an  egg.  Evidently  in  this  case  the  crescent  was  cut  first  and  the 
cavity  excavated  afterwards.  .  .  . 

The  statements  we  have  quoted  regarding  the  details  of  oviposition  of 
the  plum  curculio,  together  with  the  observations  recorded,  indicate  varia- 
tion in  details  sufficient  to  confuse  the  layman  and  even  to  puzzle  the 
expert  if  he  seek  to  cover  rightly  any  detail  with  a  general  statement  that 
will  fit  all  cases.  Two  conclusions  are  open  :  either  some  individual  insects 
have  faulty  instincts  or  there  is  more  than  one  acceptable  way  of  performing 
several  of  the  details  of  oviposition.  The  writer  accepts  the  latter  conclusion. 

From  this  it  is  seen  that  the  somewhat  complicated  process 
of  egg  laying  varies  greatly  in  detail ;  that  the  time  consumed 
varies  at  least  from  fifteen  and  a  half  to  twenty-six  and  a  half 
minutes  ;  that  important  details  are  often  omitted  ;  and  that  in 
a  large  proportion  of  cases  even  the  final  object  is  not  attained. 
Knowing  these  variations,  one  is  not  surprised  to  learn  that  of 


394 


TRANSMISSION 


the  twenty  previously  recorded  observations  no  two  agreed,  and 
not  one  gave  a  complete  account  of  what  may  be  called  the 
typically  instinctive  process.  Bearing  all  these  facts  in  mind,  we 
are  not  to  suppose  that  still  more  complicated  processes  are 
successfully  carried  forward  in  every  instance,  as  we  have  been 
led  to  infer.  Instinct  is,  therefore,  not  unerring,  nor  does  it 
insure  uniformity  of  procedure.  It  looks  as  if  important  links 
in  the  chain  of  impulse  may  be  omitted,  or,  if  the  series  is  inter- 
rupted for  any  cause,  it  may  be  resumed  at  almost  any  point. 
Certain  it  is  that  different  series  are  far  from  uniform  and  that 
very  many  of  them  fail  of  their  evident  and  final  object. 

Instinctive  acts  are  not  always  adaptive  ;  their  origin  is  there- 
fore not  in  purposeful  acts.  It  is  of  necessity  true  that  in  most 
cases  instinctive  acts  are  for  the  good  of  the  species  and,  there- 
fore, by  definition,  adaptive.  If  they  were  not  for  the  good  of 
the  species  they  would  speedily  lead  to  extinction,  which  is  but 
another  way  of  saying  that  instincts  not  adaptive  have  long 
since  been  blotted  out  by  selection,  along  with  the  individuals 
in  which  they  arose. 

That  such  non-adaptive  instincts  exist,  however,  is  easily 
shown.  For  example,  when  the  moth  flies  into  the  flame  and  is 
killed,  by  no  stretch  of  the  imagination  can  this  be  called  an 
adaptive  act ;  nor  can  it  be  conceived  as  having  arisen  in  the 
purposeful  acts  of  its  ancestors.  It  never  could  have  served 
any  but  an  evil  purpose  to  the  race,  and  the  only  element  that 
now  stands  in  the  way  of  the  utter  extinction  of  races  possessing 
this  instinct  is  the  relative  infrequency  of  the  naked  flame,  so 
that  comparatively  few  individuals  suffer, —  too  few  to  affect 
either  the  race  or  its  instincts.  We  must,  therefore,  look  farther 
than  habit  for  the  origin  of  instincts. 

Instincts  originate  in  reflex  action  not  in  habit.  If  a  piece  of 
meat  be  laid  upon  the  tentacles  of  an  actinian  they  will  imme- 
diately contract,  infolding  the  meat  and  carrying  it  into  the 
mouth.  If  a  piece  of  paper  be  laid  upon  the  tentacles  no  action 
follows ;  but  if  the  paper  be  covered  with  the  juice  of  meat  the 
action  is  the  same  as  if  the  piece  were  valuable  for  food. 
Tentacles  that  have  arisen  from  a  wound  in  the  side  of  the  body 
will  react  t)  meat  and  meat  juice  as  do  the  normal  parts, 


TRANSMISSION    OF  MODIFICATIONS  395 

infolding  and  pressing  the  piece  against  the  body  as  if  endeavor- 
ing to  tuck  it  into  a  mouth,  though  none  is  present.1  Here  it  is 
not  intelligence  that  affords  the  basis  of  muscular  contraction 
but  chemical  action  of  the  meat  juices  upon  the  muscle  fibers  of 
the  tentacles.  -The  same  principle  governs  motion  and  secretion 
in  insectivorous  plants,  to  which  no  one  would  ascribe  even  the 
elements  of  intelligence.  Odors  excite  the  salivary  glands  and 
make  the  mouth  water,  but  it  is  contact  that  starts  the  secre- 
tion of  gastric  juice  in  the  stomach. 

Light  stimulates  specific  reactions  in  many  forms  of  proto- 
plasm, and  many  tissues  contract  under  its  influence.  It  is  this 
contraction  that  causes  the  bending  of  stems  toward  the  light. 
The  iris  of  the  eye  contracts,  not  by  nervous  impulse  but  by 
the  action  of  the  light,  causing,  directly,  muscular  contraction. 
Loeb  reports  2  that  he  has  often  observed  the  contraction  of  the 
iris  of  dead  sharks  under  the  influence  of  light  "  several  hours 
after  death,  when  signs  of  decomposition  had  already  begun 
to  appear." 

Long-bodied  insects,  if  lying  with  the  side  to  the  light,  will, 
because  of  this,  have  their  bodies  bent,  with  the  concave  side 
next  to  the  source  of  light  if  positively  heliotropic.  Whenever 
they  move  in  this  condition  they  must  of  necessity  move  in  a 
curved  instead  of  a  straight  line,  until  such  time  as  they  are 
headed  directly  toward  the  light.  From  that  time  the  body  is 
equally  illuminated  on  both  sides.  It  therefore  becomes  and 
remains  straight,  so  that  future  motion  must  be  in  a  straight 
line,  any  deviation  being  quickly  corrected  by  the  unequal  illumi- 
nation of  the  body.  It  is  this  series  of  facts,  arising  from  the 
natural  relation  between  light  and  protoplasm,  and  not  curiosity, 
that  accounts  for  the  flying  of  the  moth  into  the  candle.  Nega- 
tively heliotropic  animals  would  of  course  behave  in  exactly  the 
opposite  manner,  but  for  the  same  general  reasons. 

Insects  and  small  worms  are  said  to  burrow  into  dark  places 
for  the  purpose  of  hiding.  This  cannot  be  true,  for  under  direct 
experiment  small  animals  often  emerge  from  darkness  to  light, 
from  hiding  to  exposure,  under  the  impelling  force  of  an  in- 
stinct to  bring  their  bodies  into  contact  with  as  many  surfaces  as 

1  Loeb,  Physiology  of  the  Brain,  pp.  48-54.  2  Ibid.  p.  40. 


396  TRANSMISSION 

possible.  In  a  box  they  will  crawl  along  the  bottom  till  they 
come  to  a  side.  Here  they  can  touch  two  surfaces,  and  motion 
will  then  be  along  the  groove  where  the  side  meets  the  bottom 
until  they  reach  the  corner,  where  a  third  surface  joins,  when 
they  are  likely  not  to  turn  the  corner  (unless  impelled  by  some 
stronger  instinct)  but  to  come  to  rest  in  contact  with  three 
surfaces,  this  affording,  apparently,  the  highest  attainable  satis- 
faction. If  a  tubular  opening  be  found,  insects  of  this  instinct 
will  crowd  into  it,  if  possible,  or  at  least  make  the  attempt.1 
This  instinct  to  seek  greater  comfort  by  getting  snugly  placed 
in  contact  with  foreign  bodies  is  present  in  the  higher  animals 
and  in  man,  and  it  accounts  for  many  of  the  movements  and 
resting  positions  so  commonly  seen. 

That  this  action  is  not  the  result  of  a  purpose  to  hide  is 
evidenced  by  the  fact  that  neither  light  nor  darkness  has  any 
effect  upon  it,  and  that  the  instinct  is  not  changed  even  by  the 
removal  of  the  brain.  In  nature,  of  course,  places  that  will  satisfy 
this  instinct  are  generally  shut  away  from  light,  and  insects  so 
bestowed  are  also  hidden,  —  a  fact  that  has  given  rise  to  the 
tradition  that  the  purpose  was  to  secrete  themselves  from  pred- 
atory enemies.  Of  course  the  tradition  itself  is  not  consistent, 
for  intelligent  animals  seeking  food  soon  learn  the  favorite  haunts 
of  their  prey.  They  therefore  know  precisely  where  to  look  for 
them  and  speedily  turn  them  out. 

We  have  already  seen  that  protoplasm  may  be  excited  to 
action  by  a  great  variety  of  external  agents  (light,  heat,  elec- 
tricity, chemical  substances) ;  that  the  character  of  protoplasmic 
activity  may  be  modified  by  certain  of  these  external  forces, 
notably  light  and  chemical  attraction ;  that  the  direction  of 
movement  or  of  growth  may  also  be  influenced  by  the  same 
class  of  agents  (light,  chemical  substances,  heat,  gravity) ;  and 
that  in  all  these  ways  the  activities  of  living  beings  are  largely 
dependent  upon  the  nature  of  the  outside  forces  with  which  they 
come  into  contact.  Here  lies,  to  a  very  large  extent,  the  initial 
cause  of  those  external  acts  we  ordinarily  speak  of  as  instincts, 
and  the  remaining  elements  of  causation  are  to  be  sought  in  the 
internal  mechanism  of  the  creature.  In  all  likelihood  it  is  not 

1  Loeb,  Physiology  of  the  Brain,  p.  93. 


TRANSMISSION  OF  MODIFICATIONS  397 

too  much  to  say  that  in  the  last  analysis  instinct  is  a  function 
of  structure  ;  that  the  ultimate  causes  of  instinctive  acts  lie  in 
the  nature  and  the  surroundings  of  the  protoplasm,  —  its  internal 
activities  upon  the  one  hand  and  its  natural  reactions  to  accidental 
contact  with  outside  forces  upon  the  other. 

If  this  be  true,  then  the  causes  of  instincts  lie  in  the  structure 
of  the  organism,  —  using  the  word  "structure"  in  its  broadest 
sense,  chemical  and  physiological  as  well  as  anatomical.  Thus  if 
a  new  creature  should  suddenly  be  created,  its  instincts  could  be 
fairly  well  foretold  by  any  one  who  knew  the  morphology  of  its 
structure  and  the  nature  of  its  protoplasm.  Three  fundamental 
facts  should  be  borne  in  mind  in  this  connection  : 

1.  Any   living   being  will  make  use  of   any  organ,  part,  or 
faculty  with  which  it  is  endowed  by  birth. 

2.  The  impulse  to  make  use  of  a  part  may  arise  either  from 
within  (desire)  or  from  without  (light,  heat,  chemical  action, 
gravity,  electricity,  contact). 

3.  Manifestly  the  acts  of  an  organism  are  limited  to  its  natural 
organs  and  faculties.    Therefore  instincts,  like  intelligent  acts, 
differ,  being  restricted  to  the  range  of  natural  endowment, — a 
restriction  which  no  amount  of  "  willing  "  will  remove  or  modify. 

Intelligence  not  necessary  to  the  control  of  even  complicated 
acts.  At  first  thought  it  seems  incredible  that  a  long  and  com- 
plicated series  of  acts,  culminating  in  a  purposeful  end,  can  be 
directed  by  any  other  agency  than  intelligence.  Yet  such  is  the 
fact,  and  a  mistake  at  this  point  has  led  more  than  one  evolu- 
tionist into  fatal  error. 

When  we  see  an  insect  light  upon  a  particular  part  of  a  partic- 
ular animal,  sting  it  perhaps  in  such  a  manner  as  to  paralyze  but 
not  to  kill,  drag  it  to  a  cavity  wherein  eggs  have  been  deposited, 
store  it  away  as  food  for  the  larvae,  seal  all  up  safely  as  if  with  the 
greatest  care,  it  is  difficult  not  to  attribute  the  highest  intelligence 
and  the  most  careful  foresight  to  so  remarkable  a  series  of  acts. 

Yet  we  are  not  to  be  deceived  by  the  attitude  of  busy  pre- 
occupation or  the  appearance  of  intelligent  effort.  Acts  as  com- 
plicated as  these  are  going  on  about  us  every  day,  with  no  sug- 
gestion of  intelligent  control.  The  growth  of  the  embryo  in 
utero,  and  the  vital  processes  generally,  are  even  more  orderly 


398  TRANSMISSION 

and  complicated  than  those  semi-mechanical  acts  connected  with 
the  deposition  of  eggs  and  the  care  of  young,  which  are  them- 
selves in  their  essence  not  far  removed  from  vital  processes. 

All  motion  is  reducible  to  irritability  and  contractility  of 
protoplasm  as  its  ultimate  cause,  and  any  impulse  that  will  pro- 
duce this  effect  will  lead  to  action.  Furthermore,  this  action 
must,  from  the  nature  of  the  case,  be  characteristic  of  the 
organism  and  its  peculiar  mechanism. 

It  has  been  held  that  all  muscular  activity  must  have  its  origin 
in  a  nerve  stimulus  of  some  sort.  That  this  is  erroneous  is  self- 
evident.  Muscle  tissue,  unsupplied  with  nerve,  is  still  contract- 
ile, and  the  impulse  can  still  be  supplied  from  a  variety  of 
sources  (heat,  light,  electricity,  contact). 

Nervous  impulse  is  but  one  out  of  many  stimuli  to  muscular 
contraction,  or  other  activity  of  living  protoplasm,  though  it  is 
the  most  rapid  and  direct,  and  the  one  most  readily  under  con- 
trol of  the  mind  and  the  will.  Restating  the  proposition,  nervous 
mechanism  is  not  necessary  to  motion,  not  even  to  coordinated 
'motion  of  a  high  degree,  but  it  is  necessary  to  the  highest  coor- 
dination of  the  most  complicated  organisms ;  it  is  necessary  as 
the  means  by  which  the  will  may  quickly  reach  all  parts  of  the 
machine  and  direct  or  set  aside  mere  instinctive  motion ;  it  is 
necessary  for  the  realization  of  all  the  possibilities  of  which  a 
highly  organized  structure  is  capable ;  it  is  not  necessary  to 
action,  or  even  to  a  high  degree  of  complication  in  action. 

Any  effective  impulse  will  serve  to  stimulate  to  activity ; 
and,  in  general  with  all  complicated  actions,  each  act  becomes 
the  impulse  for  the  next.  If  the  heart  of  a  frog  be  cut  into  sev- 
eral pieces  these  will  all  beat  rhythmically,  "  but  the  number  of 
contractions  will  vary  in  the  different  pieces.  The  sinus  venosus 
beats  most  rapidly,  and  the  number  of  its  contractions  in  a  unit 
of  time  equals  that  of  the  heart  before  it  was  divided.  Thus  we 
see  that  the  whole  heart  beats  in  the  rhy.thm  of  the  part  that  lias 
the  maximum  number  of  contractions  per  minute.  From  this  we 
must  assume  that  the  coordination  of  the  htarfs  activity  is  due  to 
the  fact  that  the  part  which  contracts  most  frequently  forces  the 
other  parts  to  contract  in  the  same  rhytJim"  1 

1  Loeb,  Physiology  of  the  Brain,  p.  25. 


TRANSMISSION   OF  MODIFICATIONS  399 

This  shows,  not  only  that  a  center  of  coordination  exists  in 
the  organ  itself,  independent  of  nerve  centers,  but  that  the 
action  of  one  part  becomes  the  impulse  for  exciting  action  in  its 
neighboring  part. 

Hydromedusae  of  different  rates  of  pulsation  were  united  in 
pairs  in  Loeb's  laboratory  by  the  process  of  grafting.  When  the 
union  was  complete  along  nearly  all  the  cut  edge  the  whole 
beat  synchronously,  but  when  the  union  covered  but  a  small 
area  the  two  beat  separately  with  a  different  rhythm.1 

The  heart  of  the  ascidian  is  an  elongated  tube,  beating  so  as 
to  send  the  blood  alternately  from  left  to  right  and  from  right 
to  left ;  that  is,  the  impulse  seems  to  originate  at  one  end  for  a 
time,  and  then,  after  several  hundred  beats,  to  shift  to  the  other 
end.  It  was  found  that  the  "  area  of  impulse  "  was  confined  to  a 
short  section  at  either  end ;  that  each  of  these  sections,  if  cut 
away,  continued  to  beat  rhythmically,  but  that  the  longer  middle 
part  seemed  incapable  of  contraction  without  external  stimulus. 
Commenting  on  the  fact,  Loeb  says  : 2 

These  experiments,  it  seems  to  me,  leave  no  room  for  doubt  that  the 
change  in  the  direction  in  the  contraction  of  the  ascidian's  heart  is  deter- 
mined by  each  of  the  two  ends  getting  the  upper  hand  alternately  and  forcing 
the  other  center  to  act  in  its  rhythm  for  a  time.  This  "  getting  the  upper 
hand  "  might  possibly  mean  nothing  more  than  that  one  end  gains  the  time 
in  which  to  send  off  a  wave  of  contraction  before  the  other  end  begins  to 
contract.  For  this  it  is  only  necessary  that  a  single  heart  beat  of  the  lead- 
ing end  be  delayed  or  fail  entirely,  a  phenomenon  that  also  appears  occasion- 
ally in  the  human  heart. 

Locomotion  in  the  earthworm  is  by  a  series  of  elongations  and 
contractions  of  the  successive  segments  of  the  body,  in  regular 
order  from  the  front  backward.  Nobody  ever  supposed  this  serial 
order  to  be  controlled  by  conscious  intelligence,  but  it  has  been 
assumed  to  be  due  to  the  control  of  nerve  fibers  from  the  ganglia 
along  the  dorsal  surface  of  the  body.  If,  however,  the  worm  be 
cut  in  two  and  the  parts  united  by  threads,  locomotion  is  entirely 
successful,  even  though  a  considerable  space  intervenes  between 
the  pieces.  In  this  case  contraction  proceeds  backward,  seg- 
ment by  segment,  as  in  uninjured  worms,  suffering  no  special 

1  Loeb,  Physiology  of  the  Brain,  pp.  26-27.  2  Ibid.  pp.  27-29. 


400  TRANSMISSION 

interruption  at  the  point  where  the  nerve  connection  is  severed. 
The  thread  serves  perfectly  to  carry  the  impulse  over  from  the 
last  segment  of  the  anterior  piece  to  the  first  of  the  posterior. 
The  unavoidable  conclusion  is  that  at  least  from  this  point  back- 
ward each  segment  derives  its  impulse  not  from  nerve  fibers  but 
from  the  segment  just  ahead ;  in  other  words,  that  the  motion  of 
one  part  becomes  a  stimulus  to  appropriate  action  in  a  neighbor- 
ing part. 

It  is  reported  that  Ribbert  transplanted  a  milk  gland  to  the 
ear  of  a  guinea  pig,  and  that  when  the  individual  became  preg- 
nant the  gland  commenced  to  secrete  milk.  Whatever  the 
nature  of  the  stimulus,  it  was  clearly  independent  of  nerve 
impulse.1 

It  is  a  well-known  fact  that  if  an  ant  be  removed  from  its 
nest  for  a  time  and  then  put  back,  it  will  be  critically  examined, 
but  will  be  received  again ;  if,  however,  a  stranger  ant  be  intro- 
duced, it  will  at  once  be  attacked  and  killed.  How  is  the  differ- 
ence detected  ?  This  question  is  largely  answered  by  the  fact 
that,  if  the  ant  belonging  to  the  nest  be  smeared  with  the  juices 
of  a  crushed  stranger,  it  will  at  once  be  attacked  and  killed  as 
would  the  real  stranger.2  Clearly  it  is  by  the  odor  that  the  ants 
detect  the  difference,  much  as  the  dog  recognizes  his  master  in 
daylight  or  in  the  darkness,  or  follows  a  trail  along  a  crowded 
street.  All  this  shows  that  even  a  slight  cause,  like  odor,  may 
serve  to  start  the  operation  of  a  train  of  most  remarkable  re- 
flexes, which,  once  started,  proceeds  automatically,  each  act 
operating  as  a  stimulus  to  the  next. 

This  fact  is  further  illustrated  in  the  case  of  dogs  deprived  of 
large  portions  of  the  nervous  system.  Individuals  that  have 
lost  the  spinal  cord  "  almost  up  to  the  medulla  "  may  live  for 
years  and  perform  all  normal  functions.3 

Goltz  entirely  removed  both  hemispheres  of  the  brain  from  a 
full-grown  dog.  The  first  effects  of  so  violent  an  experiment  are 
apparently  disastrous,  but  if  skillfully  done  the  shock  soon  sub- 
sides and  all  normal  ftmctions  of  the  body  proceed  as  before. 
That  is,  the  animal  performs  the  external  acts  of  eating,  urina- 
tion, defecation,  etc.,  the  same  as  when  in  possession  of  the  brain, 

1  Loeb,  Physiology  of  the  Brain,  p.  206.      2  Ibid.  pp.  220-221.      3  Ibid.  p.  43. 


TRANSMISSION   OF  MODIFICATIONS  401 

and  apparently  according  to  the  same  train  of  reflexes  that  provide 
in  life  generally  for  such  important  vital  processes  as  the  pulsa- 
tion of  the  heart,  characteristic  action  of  the  various  glands  of 
the  body,  the  movements  of  the  intestines,  etc.  All  traces  of 
memory  were  gone,  and  the  dog  could  not  recognize  its  master. 
It  would  avoid  objects  in  walking,  but  could  not  recognize  food. 
If,  however,  the  food  were  brought  in  contact  with  the  nose  or 
placed  in  the  mouth,  the  jaws  commenced  to  work  and  the  food 
was  swallowed  and  digested  as  by  any  other  dog.1 

Dogs  in  this  condition  live  for  months  or  for  years,  and  perform 
all  the  functions  of  normal  animals  not  requiring  intelligent 
action.  All  this  shows  to  what  extent  vital  actions  are  a  series 
of  reflexes  constituting  a  train,  in  which,  if  one  member  be  started 
by  appropriate  stimulus,  all  the  rest  follow  automatically. 

Instinct  not  founded  on  habit.  The  facts  that  have  been  cited 
certainly  show  that  instinctive  acts  are  nothing  but  the  putting  to 
use  of  parts  in  possession  of  the  individual  and  capable  of  action. 
They  are  in  that  way  spontaneous,  and  whatever  meaning  or 
special  significance  may  seem  to  be  involved,  it  is  to  be  sought, 
not  in  the  impulse  to  the  act,  but  farther  back  in  the  circumstances 
and  causes  that  led  to  the  development  of  the  parts,  each  with  its 
characteristic  capacity.  A  multitude  of  causes  have  taken  part  in 
the  selective  processes  by  which  the  several  organs  and  parts  of 
a  body  have  been  developed,  each  capable  of  performing  a  special 
act,  either  independently  or  as  a  part  of  a  complicated  series  ; 
but,  once  assembled,  nothing  is  more  natural  than  that  each 
should  perform  its  proper  service,  and  any  stimulus  sufficient  to 
start  the  machinery  will  of  necessity  insure  the  whole  train  of 
appropriate  results. 

Nor  are  we  to  be  deceived  by  the  appearance  of  intelligence 
as  the  acts  proceed.  The  busy  preoccupation  of  the  insect 
engaged  in  one  of  the  more  complicated  processes  of  egg  laying 
has  all  the  semblance  of  the  highest  intelligence,  but  we  must 
not  forget  that  in  many  cases  the  individual  must  be  entirely 
ignorant  of  the  final  result ;  it  will  be  dead  before  the  eggs 
hatch  ;  it  lives  but  a  single  season  and,  therefore,  neither  it  nor 
its  ancestors  ever  saw  a  larva ;  it  is  simply  playing  its  role  in  a 

1  Loeb,  Physiology  of  the  Brain,  pp.  246-248. 


402  TRANSMISSION 

wonderful  series  of  which  it  is  itself  but  a  part,  and  of  whose 
beginning  and  end  it  is  alike  ignorant. 

The  instinct  to  suck  cannot  be  conceived  as  founded  on  habit, 
because  sucking  is  not  a  life  habit  with  any  individual.  It  is 
practiced  but  a  brief  season  after  birth,  and  then  abandoned, 
leaving  no  trace  or  even  impulse  behind. 

It  is  difficult  for  us  to  dissociate  these  complicated  acts  from 
the  idea  of  intelligent  control.  Yet  many  of  them  are  performed 
by  plants,  in  which  there  is  not  so  much  as  the  beginnings  of  a 
nervous  system,  the  impulse  traveling  from  cell  to  cell,  as  it  is 
entirely  capable  of  doing  in  animal  tissue,  but  at  a  rate  easily 
overtaken  by  nerve  transmission,  whenever  the  latter  is  superim- 
posed by  the  will  or  otherwise. 

Again,  we  must  consider  the  exceedingly  complicated  nature 
and  serial  order  of  the  vital  processes  generally.  Most  of  these 
processes,  it  is  true,  aside  from  copulation,  the  laying  of  the  egg, 
and  the  care  of  the  young,  are  carried  on  inside  the  body,  and 
therefore  out  of  sight  of  the  observer.  If  we  could  by  some 
mental  microscope  see  not  only  the  pulsation  of  the  heart,  the 
movements  of  the  stomach  and  intestines,  and  the  discharge  of 
accumulated  secretions,  but  also  the  internal  acts  of  secretion 
going  on  within  the  various  glands  of  the  body,  with  the  associated 
protoplasmic  motion  and  cell  division,  actively  accompanied  by 
the  careful  division  of  the  chromosomes  into  exactly  equal  por- 
tions qualitatively  as  well  as  quantitatively  —  if  we  could  see 
all  this  as  we  see  external  instinctive  acts,  we  should  be  led  to 
marvel  at  the  mystery  and  the  complication  of  vital  activity  in 
general.  We  should  involuntarily  seek  a  basis  of  intelligent  con- 
trol within  the  organism,  whereas  we  know  that  the  proper 
place  to  seek  causation  is  outside  the  creature  in  the  forces 
that  shaped  its  development  and  in  the  higher  power  that  en- 
dowed it  all  with  life,  whose  characteristic  act  is  motion  and 
appropriation  of  new  material.  We  are,  therefore,  not  to  be 
misled  by  the  complexity  of  acts  having  the  appearance  of 
intelligence. 

We  have  been  led  to  project  intelligence  too  far  down  the 
scale.  It  may,  if  present,  take  hold  of  and  overrule  most  (not  all) 
instinctive  acts,  but  the  vast  majority  of  organic  activities  go  on 


TRANSMISSION   OF  MODIFICATIONS  403 

without  it.1  Young  things  have  little  or  no  sense  of  fear  at 
birth,  and  at  the  first  consciousness  of  fear  make  nothing  like 
intelligent  discrimination.  The  young  chick,  so  Lloyd  Morgan 
tells  us,  is  as  much  afraid  of  a  flying  newspaper  as  of  a  hawk, 
and  has  no  preconceived  notion  of  the  danger  from  bees,  which 
can  sting,  as  compared  with  that  from  flies,  which  are  harmless. 
Its  first  fears  are  of  "largish  things,"  but  experience  rapidly 
informs  it  of  specific  things.  It  has  at  first  no  appreciation  of 
water  as  water,  but  when  it  accidentally  pecks  at  a  shining  drop 
and  wets  the  bill,  the  presence  of  the  water  starts  the  series  of 
reflexes  and  the  chick  holds  up  its  head  to  swallow,  or,  if  a  duck, 
it  "shovels,"  —  each  organism  reacts  in  its  own  characteristic 
manner,  —  and  both  learn  rapidly  by  experience.2 

Habits  follow  and  are  founded  upon  instincts.  The  true  order 
seems  to  be  that  the  earliest  attempts  are  instinctive,  but  that 
they  are  rapidly  shaped  up  and  perfected  by  experience,  and  in 
this  condition  they  become  habitual.  It  also  appears  that  no 
exact  line  can  be  drawn  between  what  we  call  instinct  and  what 
is  nothing  but  response  to  stimuli.  Manifestly  we  have  applied 
the  word  "  instinct  "  to  those  reflex  acts  that  have  the  appearance 
of  being  purposeful.  It  would  apply  equally  as  well  to  many  acts 
clearly  reflex,  and  when  it  is  shown  that  these  so-called  instinc- 
tive acts  are  themselves  only  reflexes  and  can  be  performed  per- 
fectly in  the  absence  of  all  possible  application  of  intelligence, 
either  on  the  part  of  the  individual  or  of  its  ancestors,  it  appears 
that  our  present  use  of  the  word  is  a  convenience  rather  than  a 
fair  mark  of  a  scientific  distinction. 

The  theory,  therefore,  which  places  habit  at  the  point  of  origin 
of  instinctive  acts  clearly  takes  it  out  of  its  proper  order  in  the 
series.  It  is  a  property  of  the  individual  rather  than  of  the  race, 
—  except  as  we  speak  of  the  habit  of  a  race,  meaning  there- 
by the  habit  developed  by  all  or  most  of  the  members  of  the 
race.  The  common  development  of  such  a  habit  is  not  unnatural 
since  all  of  the  individuals  of  the  race  possess  the  same  organs 

1  The  action  of  the  heart  and  of  the  secreting  organs  is  beyond  the  control  of 
the  will,  and  that  of  the  intestines  is  largely  so  ;  but  many  parts  of  the  organism 
aj-e  under  control  either  of  the  will,  of  impulses  internal  to  the  part,  or  of  causes 
external  to  the  organism.  2  Morgan,  Habit  and  Instinct,  pp.  40-90. 


404  TRANSMISSION 

and  are  for  the  most  part  subjected  to  the  same  surrounding 
conditions. 

Carefully  examined,  this  field,  interesting  as  it  is  of  itself,  is 
barren  of  evidence  upon  the  transmission  of  habits,  though  it 
is  the  one  most  often  appealed  to  for  proof  of  the  inheritance 
of  acquired  characters.  The  error  lies  in  assuming  a  causative 
relation  between  two  acts  which  are  similar.  It  is  true  that  the 
habits  of  the  individual  and  the  instincts  of  the  race  are  similar. 
They  could  not  be  otherwise,  seeing  that  both  depend  upon  the 
presence  of  suitable  organs,  without  which  the  particular  act 
would  not  be  possible,  and  with  which  it  is  certain  to  appear 
whenever  suitable  stimulus  is  encountered ;  but  habit  is  founded 
upon  instinct  and  not  instinct  upon  habit. 

The  conclusion  which  seems  inevitable  is  this  :  that  breeders 
need  have  no  fear  that  the  habit  of  an  individual,  as  such,  vvill  be 
inherited  by  its  offspring  ;  but  the  fact  that  the  habit  developed  at 
all  is  sufficient  reason  for  knowing  that  its  development  is  always 
possible  in  the  family  line,  whenever  suitable  conditions  arise. 

The  attention  of  the  student  is  called  to  the  fact  that  while 
we  have  shown  that  instinct  is  not  the  result  of  habit,  and  there- 
fore that  its  existence  is  no  proof  of  the  transmission  of  habitual 
acts,  yet  this  does  not  show  whether  or  not  the  habitual  use  or 
non-use  of  a  part  will  affect  the  intensity  of  transmission  of  that 
part,  or  the  tendency  to  make  use  of  it.  Having  put  instinct 
behind  us  where  it  properly  belongs,  we  have  now  to  inquire  into 
the  effects  of  use  and  disuse. 

SECTION   VII  —  EVIDENCE   FROM  USE  AND  DISUSE 

The  question  is  not  whether  use  develops  and  disuse  leads  to 
non-development  or  degeneracy.  The  facts  on  that  point  are 
already  well  known.  The  inquiry  is  whether  the  effects  of  use 
and  disuse  are  transmitted  ;  whether  their  influence  is  direct, 
not  merely  indirect  by  rendering  the  individuals  less  or  more 
able  to  meet  the  demands  of  selection ;  whether  specialization 
of  a  part  is  in  any  way  due  to  use,  aside  from  its  effect  in 
developing  individuals  separately  and  aside  from  its  connection 
with  increased  rigor  of  selection ;  whether  generalization  and 


TRANSMISSION   OF   MODIFICATIONS  405 

degeneracy  —  beyond  under-development  in  individuals,  or  as 
associated  with  cessation  of  selection — are  in  any  way  the  result 
of  disuse  ;  whether  an  individual  is  a  better  parent  after  a  long 
course  in  exercise  or  training,  or  a  worse  one  after  a  long  life 
of  idleness,  than  the  same  individual  would  have  been  before ; 
whether  a  race  horse  will  transmit  better  speed  after  he  or  she 
has  been  "  developed,"  and  has  made  a  record  on  the  track,  than 
he  or  she  would  have  transmitted  if  never  tracked  ;  whether  the 
later  children  of  a  studious  or  of  an  athletic  man  (or  woman) 
will  be  born  with  more  ability  in  these  directions  than  the  earlier 
ones,  and  whether  the  younger  children  of  criminals  are  more 
inclined  to  criminality  than  are  those  born  before  the  criminal 
instincts  were  fully  developed  in  the  parents.  The  real  question 
is  this  :  Is  transmission  augmented  or  lessened  by  the  degree  of 
development  to  ivldcJi  racial  characters  have  attained  in  the  indi- 
vidual before  parentage,  and  without  reference  to  selection  ? 

In  the  opinion  of  the  writer  there  is  not  yet  sufficient  evi- 
dence on  which  to  base  a  final  decision,  and  much  as  we  all 
desire  a  settlement  of  the  matter,  and  much  as  we  need  to 
know  what  the  real  truth  is,  nothing  is  gained  by  passing  pre- 
mature judgment,  and  the  question  must  be  left  for  the  time 
unanswered. 

For  the  present  the  student  must  content  himself  with  learn- 
ing to  know  the  field  of  discussion,  and,  inasmuch  as  he  must 
hold  his  opinions  in  abeyance,  it  is  important  that  he  know  the 
arguments  pro  and  con.  If  he  do  this,  and  keep  his  ear  to  the 
ground,  he  will  find  the  question  clearing  up  rapidly  in  the  near 
future  ;  we  may  be  nearer  its  solution  than  the  most  careful 
biologists  have  yet  dared  to  hope. 

Not  going  back  of  the  fact  that  no  somatic  variation  can  pos- 
sibly become  blastogenic,  Weismann  and  his  followers  deny  in 
toto  all  possibility  of  such  transmission,  although  Weismann  him- 
self has  admitted,  as  a  result  of  his  own  experiments  with  the 
colors  of  butterflies  as  dependent  upon  temperature,  that  such 
all-pervading  conditions  as  heat  may  penetrate  to  the  germ  and 
affect  its  character  as  well  as  that  of  the  tissues  of  the  body. 
In  the  opinion  of  many  recent  writers  the  list  of  "  all-pervading" 
influences  includes  much  more  than  temperature  alone. 


406  TRANSMISSION 

Weismann's  exact  words  concerning  the  two  varieties  of 
butterflies  —  the  darker  Italian  and  the  lighter  German  —  are 
as  follows  : l  "  The  two  varieties  may  have  originated  owing  to 
a  gradual  cumulative  influence  of  the  climate,  the  slight  effects 
of  one  summer  or  winter  having  been  transmitted  and  added  to 
from  generation  to  generation";  and  again,2  "  In  many  other 
animals  and  plants  influences  of  temperature  and  environment 
may  very  possibly  produce  permanent  hereditary  variations  in  a 
similar  manner "  ;  and  still  again,3  "  Many  varieties  of  plants 
may  also  be  due  wholly  or  in  part  to  the  simultaneous  variation 
of  corresponding  determinants  in  some  part  of  the  soma  and  in 
the  germ  plasm  of  the  reproductive  cells,  and  these  variations 
must  be  hereditary.  Temperature,  and  nutrition  in  its  widest 
sense,  affect  the  whole  body  of  the  plant  —  the  somatic  cells  as 
well  as  the  germ  cells."  4 

In  all  this  it  must  be  noted  that  Weismann  limits  action  of 
this  kind  to  such  external  influences  as  are  able  to  penetrate  the 
organism  and  affect  the  germ  plasm  directly ;  whether  an  influ- 
ence does  this  is  to  be  determined  in  every  case  by  direct  ex- 
periment, and  is  not  to  be  assumed  from  the  effect  of  the  same 
influence  upon  mere  body  development. 

These  citations  from  Weismann,  while  not  especially  bearing 
upon  the  topic  of  use  and  disuse,  are  introduced  because  his 
position  as  the  leader  in  opposition  to  the  theory  of  the  trans- 
mission of  modifications  due  to  external  influences  is  often  mis- 
understood. They  are  introduced  at  this  point  because  it  is 
concerning  use  and  disuse  that  the  most  vigorous  discussions 
have  arisen. 

Those  believing  in  the  transmitted  effects  of  use  and  disuse 
base  their  belief  mainly  upon  the  method  of  proof  by  instance, 
and  most  of  them  cite  instances  that  were  far  better  omitted. 
As  long  as  one  side  depends  upon  simple  enumeration,  and 
the  other  mainly  upon  abstract  reasoning,  we  are  not  likely  to 
get  ahead.  As  all  forms  of  acquired  characters  are  discussed 
together,  it  is  practically  impossible  to  cite  references  dealing 
exclusively  with  use  and  disuse ;  but  in  order  that  the  student 

1  Weismann,  Germ  Plasm,  p.  400-406.  8  Ibid.  p.  406. 

2  Ibid.  p.  405.  *  Italics  are  mine. 


TRANSMISSION   OF  MODIFICATIONS  407 


may  do  his  own  thinking,  some  of  the  principal  references  relat- 
ing in  part  to  use  and  disuse  are  given  in  the  footnote.1 

It  is  important  that  we  know  the  truth  in  this  matter  if  pos- 
sible. If  the  perfection  of  development  that  comes  only  with 
use  is  to  any  extent  transmitted,  then  we  must  put  our  speed 
horses  through  a  long  course  of  training  and  develop  them  fully 
before  we  may  hope  that  they  will  transmit  maximum  speed. 
If  this  theory  be  correct,  then  the  heifers  from  a  mature  cow 
that  has  been  long  in  milk  and  made  record,  will  be  capable 
of  developing  into  better  milkers  than  would  be  possible  if 
the  dam  had  never  made  extreme  records,  or  than  would  be 
possible  with  the  earlier  calves  from  the  same  cow  (before  the 
extreme  records  were  made).  Manifestly  the  age  of  the  bull 
will  not  count,  as  he  is  incapable  of  developing  this  particular 
character.  All  he  can  do  is  to  transmit,  unaugmented  and 
unchanged,  the  hereditary  faculties  of  milk  production  exactly  as 
they  descended  to  him.  In  meat  production  of  course,  as  in  speed, 
the  case  would  be  different,  as  both  sexes  may  be  conceived  as 
capable  of  adding  to  (?)  or  detracting  from  (?)  the  racial  intensity 
by  reason  of  their  own  development  or  lack  of  development. 

This  subject  is  now  under  investigation,  and  while  the  point 
would  seem  to  be  easy  of  determination,  yet  it  involves  the  care- 
ful study  of  all  the  progeny  of  many  individuals  both  before  and 
after  development.  On  this  point,  however,  evidence  may  be 
expected  at  no  very  distant  date. 

Effect  of  development  upon  transmission  of  speed  in  horses. 
In  a  recent  series  of  articles,2  Casper  L.  Redfield  takes  the 
position  that  the  effects  of  speed  development  are  transmitted, 
and  he  cites  numerous  instances  calculated  to  show  that  maxi- 
mum speed  is  transmitted  only  from  sires  with  long  and 

1  Against  transmission  :  Weismann,  Germ  Plasm,  pp.  392-410.    In  favor  of 
transmission  :  Romanes,  Darwin  and  After  Darwin,  II,  60-287  ;  Cope,  Origin  of 
the  Fittest,  pp.  194-203,   405-421,  and  Primary  Factors  of  Organic  Evolution, 
pp.  246-384;  Eimer,  Organic  Evolution,  pp.   153-173,   205-221.    Non-Partisan: 
Lloyd  Morgan,  Habit  and  Instinct,  pp.  280-322  ;  Vernon,  Variation  in  Animals 
and  Plants,  pp.  352-370. 

2  Mr.  Redfield's  theories  are  best  set  forth  in  a  series  of  articles  entitled  "  Evo- 
lution of  the  Setter,"  in  American  Field,    LXII,  Nos.  25-27,  and  LXIII,  Nos.  1-9. 
They  are  further  set  forth  in  a  series  entitled,  "  Breeding  the  Trotter,"  published 
in  The  Horseman,  XXV,  Nos.  19-34. 


408  TRANSMISSION 

honorable  racing  records.  The  studies  would  be  more  conclu- 
sive if  they  included  larger  numbers  of  examples,  and  if  these 
were  thrown  into  two  classes,  —  one  gotten  after  the  records 
were  made,  the  other  gotten  by  the  same  sires  before  their 
development. 

Mr.-Redfield  conceives  that  the  sire  or  dam  that  is  constantly 
worked  up  to  a  safe  limit  develops  thereby  a  larger  stock  of 
what  he  calls  "dynamic  force,"  and  that  transmission  is  in  pro- 
portion to  the  extent  of  this  force  present  at  the  time  of  procre- 
ation. There  is  no  need  of  involving  the  subject  with  new  terms. 
What  is  in  Mr.  Redfield's  mind  is  doubtless  the  same  thought 
that  lies  at  the  basis  of  Cope's  theory  of  growth  force,  which  is 
one  of  the  strongest  of  what  may  be  called  the  dynamic  theories 
of  evolution.  Everybody  recognizes  a  dynamic  basis  in  trans- 
mission, —  that  which  is  connected  with  the  intensity  of  the 
vital  processes.  Many  forces  cause  that  intensity  to  vary,  and 
the  important  question  is  whether  exercise,  use,  extreme  devel- 
opment in  the  individual,  is  one  of  them.  Mr.  Redfield's  articles 
may  be  read  with  profit ;  whether  or  not  all  his  conclusions  will 
stand  is  another  matter.  The  articles  are  chiefly  useful  for  the 
large  mass  of  facts  presented,  which,  good  as  they  may  be,  are 
not  yet  sufficient  to  maintain  his  theories  or  to  answer  the  ques- 
tion that  horsemen  would  like  to  have  settled. 

Certain  outside  considerations  must  be  borne  in  mind  in 
studying  this  subject : 

1.  The  better  the  sire  as   to  speed,  the  better  will  be  his 
opportunity  to  get  speed,  for  the  more  numerous  will  be  his 
offspring  and  the  better  will  be  the  class  of  mares  offered.    The 
same  principle  holds  true  as  to  the  dam,  for  only  a  good  one  is 
worth  the  fee  for  a  high-class  stallion ;  in  other  words,  the  sires 
and  dams  with  records  have   better  opportunities  to  produce 
than  do  those  equally  good  but  without  records.    Because  of 
this  fact  the  get  of  one  animal  must  be  compared,  not  with  that 
of  another,  but  with  his  own  of  a  later  or  earlier  date. 

2.  Speaking  generally,  the  get  of  the  best  horses  later  in  life, 
after  they  are  known  to  be  valuable,  will  be  better  trained  and 
better  developed  than  the  get  of  the  same  animals  earlier  in 
life  and  in  the  hands  of  more  ordinary  horsemen. 


TRANSMISSION   OF  MODIFICATIONS  409 

3.  So  much  of  this  exercise,  or  development,  as  contributes 
simply  to  constitutional  vigor  and  good  health  will  have  its  effect 
under  quite  another  principle.  Moderate  exercise  over  against 
absolute  inactivity  should  show  some  results,  but  this  is  entirely 
outside  the  present  inquiry.  What  we  desire  to  know  is  whether 
the  extreme  development  of  a  faculty  in  an  individual  will  aug- 
ment its  transmission  above  what  would  otherwise  have  been  the 
transmitting  power  of  that  individual. 

Mr.  Redfield's  conclusion  that  this  transmission  is  limited  to 
the  same  sex  —  that  the  development  of  a  sire  affects  only  his 
male  offspring  —  does  not  rest  upon  good  grounds,  and  is  against 
what  is  generally  known  as  to  sex  transmission.  It  will  be  seen 
later  that  sires  are  slightly  but  not  noticeably  prepotent  over 
dams  in  male  offspring,  and  vice  versa ;  but  the  difference  is 
slight,  and  not  marked,  so  far  as  it  has  yet  been  studied  by  the 
statistical  method,  which  is  the  only  reliable  one  for  the  deter- 
mination of  questions  of  this  character. 

Effect  of  development  upon  the  transmission  of  milking  quality. 
It  is  a  widespread  belief  that  a  heifer  will  make  a  better  cow  if 
brought  into  milk  at  two  years  of  age  than  she  will  make  if  her 
milking  powers  are  not  developed  till  later.  Will  her  later 
calves,  dropped  say  at  six  years  of  age,  be  influenced  by  the  fact 
that  she  was  a  cow  at  two  years  of  age  rather  than  not  until  four 
or  five  ?  The  question  cannot  be  answered  at  present,  though 
records  are  accumulating  which  will  almost  certainly  afford  an 
answer  in  the  near  future.  In  the  meantime  it  is  both  fruitless 
and  hazardous  to  speculate.  We  must  turn  in  another  direction 
for  the  only  known  evidence  that  is  valuable,  and  reason  by 
inference  from  the  behavior  of  characters  under  degeneration. 

SECTION  VIII  —  EVIDENCE  FROM   DISAPPEARING 
ORGANS 

It  seems  to  be  true  in  general  that  when  a  part  once  useful  is 
no  longer  used,  its  doom  is  sealed.    It  at  once  begins  to  degen- 
erate and  its  final  disappearance  seems  only  a  question  of  time. 
In  this  way  the  snake  has  lost  all  its  limbs  ;  *  the  whale,  its  hind 
1  The  python  still  has  rudiments  of  the  pelvic  bones. 


410 


TRANSMISSION 


limbs  ;  the  wings  have  gone  from  the  apteryx  and  appear  to  be 
going  from  the  ostrich  ;  eyes  of  cave  insects  and  fishes  are  in 
many  cases  imperfect  or  rudimentary ;  horses,  cattle,  sheep, 
and  hogs  have  lost  toes  that  belonged  to  their  ancestors,  and 
parts  generally  which  are  functionless  are  evidently  disappearing. 
How,  now,  are  parts  lost,  when  once  they  have  become  useless  ? 

Economy  of  Nature  not  the  reason  for  loss  of  parts.  It  is 
sometimes  said  that  a  part  no  longer  used  is  removed  by  Nature 
in  the  interest  of  economy.  This  is  bad  science.  Nature  is  not 
economical.  She  not  only  supports  many  expensive  and  useless 
parts,  such  as  tremendous  horns  and  tusks,  but  she  often  pro- 
duces necessary  products  in  wanton  profusion,  such  as  pollen 
and  fat.  Other  and  deeper  causes  are  at  work,  —  causes  more 
rationally  connected  with  the  facts  of  life,  —  than  any  such 
anthropomorphic  reason  as  economy.  Whatever  may  be  true 
as  to  economy  of  growth,  it  is  a  fact,  not  a  principle ;  a  result, 
not  a  cause. 

How  parts  disappear.  We  are  reasonably  intelligent  upon  a 
part  of  the  process  of  degeneracy  and  disappearance,  at  least  in 
the  more  active  portions  of  the  body.  As  long  as  a  part  is  in 
use,  its  constant  movements  increase  the  flow  of  blood  to  that 
part  and  it  enjoys  the  extreme  development  that  comes  only  with 
maximum  nourishment  and  uniform  healthy  exercise.  When, 
however,  the  part  is  no  longer  used,  the  flow  of  blood  is  lessened 
and  it  suffers  from  lessened  nourishment.  In  this  way  the  first 
steps  of  degeneration  are  easily  accounted  for. 

If  the  part  has  been  useful  heretofore,  it  has  of  course  been 
sustained  by  selection.  Being  no  longer  useful,  this  influence  is 
withdrawn,  and  breeding  is  henceforth  totally  without  reference 
to  this  particular  part;  that  is  to  say,  there  is  absolute  "cessa- 
tion of  selection,"  or  panmixia,1  as  to  this  part.  Under  this  con- 
dition the  average  parentage  would  be  lower  than  heretofore,  thus 
accounting  for  a  st\\\  farther  step  in  the  downward  process. 

To  all  this  is  often  added  the  adverse  effect  of  selection, 
when  for  any  reason  that  influence  is  turned  against  the  part. 
This  "  reversal  of  selection  "  of  course  comes  only  when  a  part 
once  useful  has  become  not  merely  useless  but  detrimental.  In 

1  Romanes,  Darwin  and  After  Darwin,  II,  97-100,  291-306. 


TRANSMISSION   OF   MODIFICATIONS 


411 


such  event  there  ensues  a  third  stage  of  degeneracy.  Obviously 
the  full  effects  of  selection  will  depend  very  much  upon  the 
character  of  the  part  and  its  connection  with  the  vital  interests 
of  the  species. 

The  influences  just  mentioned  will  sufficiently  account  for  ex- 
treme degeneracy  of  a  once  active  part,  but  they  will  not  account 
for  absolute  disappearance.  Any  character  under  such  conditions 
would  decrease  to  a  low  minimum  where  its  presence  becomes 
insignificant,  and  there  it  would  remain,  but  it  would  not  abso- 
lutely disappear  except  through  some  other  agency.  That 
characters,  even  those  which  were  once  important,  do  entirely 
disappear,  leaving  not  even  rudimentary  parts,  is  evidenced  by 
the  disappearance  of  the  legs  of  snakes,  but  that  the  later  stages 
are  extremely  slow  is  shown  by  the  rudimentary  leg  bones  of 
the  python  and  the  whale. 

Degeneration  of  eyes  in  cave-dwelling  and  deep-sea  species. 
It  is  a  well-known  fact  that  the  eyes  of  cave  fishes  and  insects 
often  exhibit  all  grades  of  degeneration,  from  near  the  normal 
down  to  the  merest  rudiments.  Being  entirely  useless  under 
the  conditions  of  life,  selection  is  suspended,  and  Nature  is 
having  her  way  with  the  remnants  of  what  was  once  a  highly 
developed  organ. 

Deep-sea  fishes  are  either  in  the  same  condition  or  else  are 
supplied  with  enormous  eyes  of  a  kind  evidently  fitted  to  per- 
ceive light  rather  than  to  make  distinct  and  clear-cut  images. 

The  gradual  failure  of  parts  like  the  toes  that  have  gone  from 
the  horse,  or  the  apparently  disappearing  vermiform  appendix, 
might  be  attributed  to  some  failure  or  imperfection  in  the  germ  ; 
but  the  instance  of  disappearing  limbs  is  too  clearly  connected 
with  disuse,  and  that  of  disappearing  eyes  with  lack  of  what 
may  be  called  essential  conditions  of  development,  to  be  explained 
wholly  on  the  ground  of  imperfection  from  within  as  the  funda- 
mental cause  of  degeneracy.1 

The  final  disappearance  of  a  useless  part  is  certainly  due  to 
some  fact  other  than  the  withdrawal  or  even  the  reversal  of 
selection.  There  must  be  morphological  units  of  some  kind 

1  Light  is  evidently  essential  to  the  origin  of  the  sensitive  spot  we  call  the  eye, 
especially  in  the  formation  of  pigment. 


412 


TRANSMISSION 


resident  within  the  germ,  from  which  they  slowly  disappear 
when  no  longer  favored  by  the  conditions  of  life  and  no  longer 
sustained  by  selection.  These  vital  units,  if  ever  discovered,  will 
be  found  to  be  closely  connected  with  the  origin  of  characters 
as  well  as  with  their  preservation. 

We  shall  see  later  that,  when  a  character  is  undergoing  rigor- 
ous selection  new  and  higher  values  than  ever  before  are  constantly 
appearing.  May  not  the  reverse  be  also  true,  —  namely,  that  a 
character  on  the  decline  may  present  its  successive  decreasing 
values  because  of  influences  entirely  internal  ? 

That  disappearance  of  parts  is  not  due  entirely  to  disuse  is 
shown  by  the  fact  that  the  process  continues  long  after  the  fact 
of  disuse  could  have  the  slightest  influence.  Where  a  rudi- 
mentary tibia  further  degenerates  to  a  rudimentary  pelvic  bone, 
the  question  of  disuse  is  certainly  not  involved ;  neither  is  use 
or  disuse  involved  in  breeding  for  high  or  low  oil  in  corn,  for 
example.  Manifestly  some  biological  principle  is  involved  that 
has  not  yet  been  discovered  and  identified,  and,  as  it  is  evidently 
a  principle  fundamental  to  transmission  and  variation,  its  isola- 
tion is  exceedingly  important. 

Characters  not  dependent  upon  adaptation.  Generally  speak- 
ing, there  is  a  close  correlation  between  the  development  of  a 
character  and  its  usefulness  to  the  individual  and  the  species.1 
This  fact  has  given  rise  to  the  impression  that  all  characters 
are  dependent  upon  teleological  principles  for  their  existence. 
No  greater  error  could  be  made.  It  is  true  that  in  nature  selec- 
tion operates  mostly  along  utilitarian  lines,  and  in  this  way  after 
a  time  it  brings  most  characters  into  line  with  the  greatest 
service  and  the  closest  adaptation;  but  selection  may  operate  in 
any  direction,  even  to  the  disadvantage  of  a  species.  In  this 
case,  however,  the  response  is  to  selection,  not  to  utility. 

Neither  is  development  along  utilitarian  lines  necessarily 
true  of  those  characters  that  lie  outside  the  field  of  selection 
or  of  those  upon  which  it  operates  too  rarely  to  impress  itself. 
For  example,  the  instinct  to  fly  toward  a  source  of  light 
would  exterminate  certain  species  if  naked  fire  were  more  gener- 
ally encountered.  That  the  testicle  in  mammals  should  have 

1  Known  among  biologists  as  teleology. 


TRANSMISSION   OF  MODIFICATIONS  413 

descended  into  an  external  sac  (the  scrotum)  is  in  no  way  use- 
ful ;  on  the  contrary,  it  is  in  many  ways  unfortunate  for  the 
individual.  Again,  the  extreme  development  of  the  testes  in 
cattle,  and  especially  in  sheep,  is  most  inconvenient,  not  to  say 
dangerous.  Such  unusual  size  is  in  no  way  necessary,  as  we 
must  infer  from  comparison  with  other  species.  It  is  one  of 
the  strange  overgrowths  of  nature,  unfortunate,  but  not  suffi- 
ciently dangerous  to  destroy  the  species.  In  other  words,  here 
are  characters  upon  which  selection  has  never  fastened  its  hold, 
and  consequently  they  have  not  been  made  to  square  with  the 
highest  degree  of  utility,  and  have  not  been  brought  into  the 
closest  "  fit."  The  inference  is  unavoidable  that  the  existence 
of  a  character  is  not  absolutely  dependent  upon  its  usefulness.1 
All  this  is  matter  of  slight  consequence  in  itself,  but  it  is  of 
fundamental  importance  when  discussing  questions  touching  the 
disappearance  of  characters  and  the  transmission  of  variations. 

The  origin  of  characters.  Considerations  such  as  here  engage 
the  attention,  impel  the  student  to  raise,  in  his  own  mind  at 
least,  the  ultimate  question,  What  was  the  origin  of  racial 
characters,  and  how  did  they  come  into  being  ? 

It  may  be  humiliating,  but  it  is  certainly  necessary,  to  say 
that  we  do  not  know,  and  to  freely  confess  that  present  informa- 
tion throws  little  light  upon  the  question.  The  Lamarckians 
find  a  ready  answer  in  asserting  that  all  characters  have  origi- 
nated in  the  necessities  of  the  individual  and  the  race,  and  in 
the  influence  of  the  conditions  of  life ;  but  it  is  both  illogical 
and  unscientific  to  assume  that  an  organ  or  a  part  "  arose  "  for 
no  greater  reason  than  that  the  need  for  it  existed. 

The  opponents  of  the  Lamarckians, — among  whom  Weis- 
mann  is  the  recognized  leader,  — -  depending  as  they  do  exclu- 
sively upon  selection,  must  assume  the  preexistence  of  the 
characters  on  which  selection  may  operate,  for  selection  as  such 
can  originate  nothing;  but  this  introduces  new  difficulties,  for  all 
higher  life  is  considered  to  have  evolved  from  lower  through  the 
acquisition  of  characters  leading  to  greater  specialization.  Now 
these  differentiating  characters  must  have  arisen  sometime,  some- 
where, and  in  some  way.  Weismann  recognizes  this  difficulty  and 
1  Of  what  possible  use  is  the  "beard"  on  the  breast  of  the  turkey? 


414 


TRANSMISSION 


meets  it  by  assuming  that  the  characters  that  distinguish  the  higher 
races  were  in  some  way  impressed  upon  the  original  protoplasm 
from  without,  while  the  remote  ancestors  were  yet  in  the  single- 
celled  stage.  Thus  do  the  most  radical  "  selectionists  "  become 
Lamarckians  of  the  purest  kind  when  driven  far  enough  back.1 

But  is  this  violent  assumption  necessary  ?  Life  in  the  single- 
celled  stage  is  not  fundamentally  different  from  life  in  the  colony 
form.  A  cell  is  a  cell  in  either  case,  and  its  activity  —  what  it 
can  do  —  is  dependent  partly  upon  its  ancestry  and  partly  upon 
the  conditions  of  life,  which  are  its  opportunities.  To  be  sure, 
the  single  cell  is  more  dependent  upon  the  external  world,  and 
reacts  more  completely  to  temperature  and  other  external  forces, 
than  does  the  larger  colony  of  highly  specialized  units  (cells), 
but  this  is  a  difference  in  degree  rather  than  in  kind. 

In  the  last  analysis  we  are  driven  to  the  conclusion  either 
that  all  characters  were  created  and  implanted  in  the  original 
protoplasm,  —  so  that  living  matter,  even  in  its  simplest  form, 
has  all  the  potentialities  of  the  highest  form  of  life,  —  or  else 
that  the  peculiar  chemical  compounds  that  constitute  living  mat- 
ter are  able  not  only  to  enter  into  definite  relations  with  the 
world  at  large,  but  also,  perhaps,  to  effect,  from  time  to  time, 
new  combinations  among  themselves,  thus  acquiring  new  or 
greatly  modified  characters,  sometimes  conforming  naturally  to 
surrounding  conditions,  sometimes  not.  To  this  latter  view  the 
writer  strongly  inclines. 

A  chemical  element,  as  iron,  acquires  no  new  characters, 
though  it  behaves  differently  under  different  circumstances. 
Sulphur  is  extremely  sensitive  to  surrounding  conditions,  and 
many  of  the  organic  compounds  depend  almost  entirely  for  their 
properties  upon  the  conditions  under  which  their  peculiar  com- 
binations were  effected. 

But  when  life  enters  the  field  all  the  complications  are  infi- 
nitely multiplied,  and  when  we  are  driven  to  the  last  ditch  all 
must  agree  that  the  characters  possessed  by  living  matter  are 
to  a  large  extent  and  in  some  way  an  expression  of  the  condi- 
tions of  life.  How  these  conditions  impress  themselves  not  only 
upon  the  individual  but  also  upon  the  race  is,  in  some  cases  at 

1  Weismann,  Germ  Plasm,  pp.  415-416. 


TRANSMISSION   OF  MODIFICATIONS  415 

least  (temperature,  food,  poisons,  and  many  chemicals  not 
poisons),  both  evident  and  easy  to  understand ;  in  others  it  is 
obscure  and  uncertain  to  the  last  degree. 

Degeneracy  and  origin  contrasted.  Of  one  thing  we  are  cer- 
tain :  characters  are  disappearing  before  our  very  eyes,  and 
whole  races  are  becoming  extinct.  What  does  this  mean  ?  Is  the 
world  growing  poorer  in  possibilities  ?  Is  specialization  realized 
only  at  the  expense  of  lessened  adaptability  to  new  conditions 
later  on  ?  If  a  part  or  a  character  now  useless  degenerates  and 
disappears  will  it  ever  come  back,  or  will  a  new  one  arise  to  take 
its  place  if  necessity  for  its  presence  should  return  ? 

These  are  large  questions  —  questions  that  we  cannot  answer, 
but  that  we  must  think  about  and  take  into  consideration  in  the 
studying  and  answering  of  easier  and  smaller  questions. 

In  the  meantime  we  will  remember  that  soles,  flounders,  and 
the  flatfishes  generally  are  developing  a  new  style  of  living,1  and 
that  their  eyes  are  taking  a  new  position  with  reference  to  the 
other  body  parts.  We  will  not  forget  that  all  animals  that  live 
in  (under)  the  water,  if  of  much  size,  are  of  one  general  shape, 
—  the  shape  of  least  resistance  to  water.  That  this  is  independ- 
ent of  selection  is  shown  in  the  history  of  the  whale  and  of  the 
few  land  mammals  that  took  to  the  water  and  whose  transforma- 
tion must  have  been  comparatively  recent. 

We  will  remember  that,  while  most  "  new  characters  "  are 
but  new  combinations  and  different  adjustments  of  old  ones, 
there  is,  after  all,  progressive  development  showing  the  infusion 
of  something  practically  new  and  different.  Higher  life  differs 
from  lower  in  kind  as  well  as  in  degree.  That  it  springs  from 
the  lower  is  certain,  and  that  something  has  been  added  in  the 
process  is  no  less  certain. 

The  world  is  full  of  lowly  forms  of  life.  The  species  of  single- 
celled  organisms  that  are  known  probably  far  outnumber  existing 

1  These  fishes,  of  which  there  are  a  number  of  species,  are  symmetrical,  or 
nearly  so,  in  the  embryo  and  for  a  little  time  afterward,  so  that  at  first  they  swim 
like  any  other  fish.  The  swimming  bladder  is  defective,  however,  and  shortly  they 
tarn  to  one  side  and  lie  on  the  bottom,  generally  left  side  down,  —  though  some 
individuals  are  reversed.  In  this  position  the  left  (now  lower)  eye  travels  upward 
toward  the  other  side,  until  the  two  eyes  lie  side  by  side  on  the  right,  now  the 
upper,  side. 


416  TRANSMISSION 

species  of  highly  developed  organisms.  Is  this  the  "  raw  mate- 
rial "  out  of  which  new  species  shall  be  evolved  later  on  to  take 
the  place  of  what  is  now  so  rapidly  becoming  extinct  ?  It  is  a 
moving  panorama,  and  we  know  neither  the  beginning  nor  the 
end.  It  is  all  a  part  of  a  vast  plan  on  which  the  universe  is 
founded  by  the  Creator.  We  cannot  doubt  that  the  most  com- 
plex element  of  it  all  is  life,  nor  can  we  doubt  that  the  most 
characteristic  property  of  living  matter  is  its  progressive  devel- 
opment, bringing  to  light  new  activities  and  establishing  new 
relations  with  the  world  outside.  Whether  this  property  is  wholly 
internal  and  dynamic,  or  due,  at  least  to  some  extent,  to  outside 
influences,  —  this  is  the  chief  mystery. 

SECTION  IX  —  VARIATIONS  DUE  TO  CAUSES  NOT  AFFECT- 
ING THE  GERM  ARE   NOT  TRANSMITTED 

This  much  is  a  logical  conclusion.  This  much  is  fundamental 
and  axiomatic.  The  germinal  matter  is  the  only  material  that 
passes  over  from  generation  to  generation.  The  fertilized  germ 
is  the  only  heritage,  and  it  is  the  only  avenue  of  transmission. 
Whatever  faculties  or  endowments  the  individual  may  possess, 
he  can  transmit  only  those  which  can  find  lodgment  and  repre- 
sentation in  the  germ,  and  whether  the  causes  of  germinal 
changes  are  internal  or  external,  or  both,  no  variation  can  be 
transmitted  unless  it  affects  the  germ  or  unless  the  cause  that 
induced  the  variation  also  affected  the  germ. 

Variations  due  to  causes  internal  to  the  body  but  external  to 
the  germ  are  not  transmitted.  It  is  entirely  possible  that  certain 
variations,  either  of  structure  or  of  function,  may  arise  from 
irregularities  in  cell  division  during  development  due  to  local 
rather  than  to  germinal  causes.  For  example,  it  has  already 
been  noted  that  cells  may  at  any  time  divide  into  unequal  por- 
tions, or  into  three  instead  of  two  parts,  giving  rise  to  abnormal 
if  not  to  pathological  conditions. 

Almost  all  portions  of  the  body  are  subject  to  those  over- 
growths called  tumors,  and  while  it  is  not  yet  definitely  known 
whether  the  causes  of  abnormal  growth  are  external  or  internal 
to  the  organism,  they  certainly  are  not  located  in  the  germ. 


TRANSMISSION    OF   MODIFICATIONS  417 

The  probability  is  that  they  are  entirely  local,  sometimes  arising 
from  external  injuries,  as  in  galls,  and  thus  outside  the  present 
field  of  inquiry,  but  more  often  due  to  internal  disturbances  in 
the  cells  themselves  at  the  particular  point  where  the  abnormal 
functioning  appears. 

Modifications  due  to  external  causes  sometimes  transmitted, 
oftener  not.  The  effects  of  such  all-pervading  influences  as 
nourishment,  temperature,  chemical  action,  gravity,  etc.,  are 
not  felt  simply  by  the  external  parts,  but  on  the  contrary  they 
may  extend  to  the  innermost  parts  of  the  organism,  affecting 
the  constitution  and  the  activities  of  the  most  highly  specialized 
matter,  extending,  for  all  we  know,  to  the  very  germ,  in  which 
case  they  would  certainly  be  transmitted,  whereas  there  is  no 
ground  for  belief  in  the  transmission  of  influences  that  do  not 
affect  the  germ. 

Summary.  When  we  speak  of  the  transmission  of  a  modifi- 
cation we  mean  rather  the  transmission  of  a  character  as  modi- 
fied. Strictly  speaking,  a  character  will  be  transmitted  in  a 
modified  form  if  tJie  modification  affects  the  germ  ;  otherwise  it 
will  be  transmitted  in  an  unmodified  form,  for  the  germ  is  the 
only  hereditary  substance,  and  nothing  is  transmitted  except 
through  the  germ. 

*  A  modification  may  arise  from  causes  either  internal  or  exter- 
nal to  the  germ.  If  internal  it  of  necessity  affects  the  germ  and 
is  transmitted.  This  is  the  ordinary  cause  of  hereditary  varia- 
bility. If,  on  the  other  hand,  the  modification  arose  from  external 
causes,  the  germ  may  or  may  not  be  affected,  and  the  modifica- 
tion may  or  may  not  be  transmitted. 

There  is  much  reason  to  believe  that  many  modifications  of 
functional  activity  are  of  such  a  fundamental  nature  as  to  influ- 
ence the  germ  as  well  as  the  soma,  and  such  modifications 
would  be  transmitted  and  inherited  by  the  offspring. 

In  general,  the  great  effect  of  the  environment  is  to  influence 
development,  not  to  induce  new  characters.  The  environment 
does  not  decide  what  characters  shall  compose  the  individual, 
—  that  is  a  matter  of  straight  inheritance,  —  but  it  does  decide 
to  a  very  large  extent  what  degree  of  development  the  various 
racial  characters  shall  attain  in  particular  individuals.  The 


4l8  TRANSMISSION 

question  whether  extreme  development  tends  to  affect  the  germ 
and  to  become  inherited  is  a  question  beset  with  many  difficul- 
ties. The  greatest  obstacle  to  this  study  is  the  ever-present 
fact  of  selection,  which  rapidly  brings  about  a  close  correspond- 
ence between  organisms  and  their  surroundings.  No  reliable 
conclusion  can  be  drawn  until  this  influence  is  accounted  for 
or  eliminated. 

In  further  pursuance  of  this  study  we  now  pass  to  more  def- 
inite discriminations  as  to  type  and  to  more  exact  and  critical 
distinctions  concerning  variability  as  expressed  not  in  individuals 
but  in  numbers  sufficiently  large  to  be  fairly  indicative  of  the  race. 

ADDITIONAL  REFERENCES 

AN  EXAMINATION  OF  WEISMANNISM.    By  G.  J.  Romanes,    i  vol. 
DARWIN  AND  AFTER  DARWIN.    By  G.  J.  Romanes.    2  vols. 
DEVELOPMENT   AND   EVOLUTION.     By   J.    M.    Baldwin.     Science,   XVI, 

819-821. 
ENVIRONMENT    AND    ITS    EFFECT   ON    THE   TRANSMITTING  POWER  OF 

SEEDS.    By  W.  W.  Tracy.    Science,  XIX,  738-740. 
EXPERIMENTAL  ZOOLOGY.    By  T.  H.  Morgan.    Chapters  IV  and  V,  pp. 

43-61. 

FOUNDATIONS  OF  ZOOLOGY.    By  W.  K.  Brooks,    i  vol. 
HEREDITY   AND    INSTINCT.    By  J.  M.  Baldwin.    Science,   III,  439-44;, 

558-559- 
INHERITANCE  OF  ACQUIRED  CHARACTERS.    By  E.  D.  Cope.    Science,  V, 

633-634  ;  by  John  McFarland,  Ibid.,  935-945. 

INHERITANCE  OF  ACQUIRED  CHARACTERS.  (Examples.)  By  F.  H.  Her- 
rick.  Science,  VII,  280. 

INHERITANCE  OF  ACQUIRED  CHARACTERS.  By  D.  E.  Hutchens  (1904). 
Nature,  LXXI,  83. 

NATURE  OF  CANCERS  AND  ABNORMAL  GROWTHS,  AND  TRANSMISSIBILITY 
OF  SAME.  By  E.  B.  Bashford.  Proceedings  of  the  Royal  Society, 
London,  LXXIII,  66-67. 

RIGHT-  AND  LEFT-EYEDNESS.    By  G.  M.  Gould.    Science,  XIX,  591-594. 

THE  HEREDITY  OF  ACQUIRED  CHARACTERS.  Boston  Medical  and  Surgi- 
cal Journal,  CXXXVII,  427-428. 

USE-INHERITANCE.  Direction  of  Hair  in  Man  and  Animals  and  its  Appli- 
cation to  Darwinism.  By  W.  Kidd.  Science,  XV,  142-143;  also  in 
Science,  XX,  401-407. 


CHAPTER  XII 

TYPE  AND  VARIABILITY1 

Enough  has  been  shown  in  earlier  chapters  to  convince  the 
student  that  variability  is  an  inevitable  accompaniment  of  both 
reproduction  and  development,  and  therefore  that  variation  is  to 
be  expected  among  living  beings  everywhere. 

Before  anything  like  a  comprehensive  idea  of  transmission 
can  be  developed  therefore,  it  is  necessary  to  study,  not  indi- 
viduals, but  groups,  and  to  establish  definite  conceptions  as  to 
type  and  variability.  In  this,  as  in  any  other  critical  study  of  a 
race,  we  proceed  character  by  character,  and  are  careful  to 
include  enough  individuals  to  be  fairly  representative  of  the  race 
as  a  whole.2 

A  farmer  plants  an  ear  of  corn  say  ten  inches  in  length. 
What  he  gets  is  not  a  crop  of  ears  all  ten  inches  long,  but  a 
group  of  ears  ranging  in  length  all  the  way  from  perhaps  three 
or  four  inches  up  to  eleven  or  twelve,  or  even  a  little  more.  The 
same  principle  will  hold  if  the  ear  that  is  planted  is  nine  inches 
long  instead  of  ten,  except  that  the  distribution  will  be  different, 
lengths  running,  in  general,  slightly  lower;  that  is  to  say,  the 
length  of  ear  of  the  offspring  is  not  the  same  as  that  of  the 
parent,  but  it  constitutes  a  "distribution  "  extending  both  above 
and  below  that  length.  So  far  as  is  known,  this  principle  of  trans- 
mission holds  true  in  all  races  and  for  all  characters.  Stated  in 
more  general  terms,  we  may  say  that  the  offspring  as  a  whole  is 
not  the  same  as  the  immediate  parents,  but  that  it  constitutes  a 
distribution  extending  from  near  the  lower  to  approximately  the 
upper  limits  of  the  race.  This  suggests  at  once  the  idea  of  type 
and  that  deviation  from  type  which  ^ve  call  variability. 

1  See  Bulletin  No.  7/9,  Agricultural  Experiment  Station,  University  of  Illinois, 
by  the  author  of  this  text. 

2  Having  discovered  the  type  as  to  several  important  characters,  it  would  then 
be  possible  to  select  a  typical  individual. 

419 


420  TRANSMISSION 

SECTION  I  — TYPE 

What  now  is  our  conception  of  type  ?  If  ten-inch  ears  will 
not  produce  ten-inch  ears,  but  something  else,  and  not  only 
something  else  but  a  considerable  variety  of  lengths ;  and  if 
what  we  get  extends  both  above  and  below  the  parent,  then  we 
arrive  at  once  at  a  double  conception  as  to  type  ;  that  is  to  say, 
the  type  of  the  offspring  is  not  the  same  as  that  of  the  parent. 
The  type  of  the  parent  is  very  definite,  representing  an  ideal ; 
but  if  the  offspring  is  distributed  both  above  and  below  that 
ideal,  some  being  better  and  some  not  so  good,  then  a  close 
analysis  of  the  real  character  of  that  offspring  becomes  necessary 
in  order  to  make  any  just  comparison  between  the  two,  or  to 
arrive  at  any  adequate  conception  of  type  in  a  mixed  population, 
even  in  one  arising  from  a  selected  ancestry. 

A  concrete  case  will  serve  best  to  illustrate  the  principle 
involved.  In  the  year  1906  some  Learning  corn  was  raised  on 
good  ground  from  seed  ears  exactly  ten  inches  in  length.  A 
random  sample1  of  this  crop,  consisting  of  327  ears,  gave  the 
following  distribution  as  to  length  : 

One  ear  was  3.0  inches  long,  one  was  4.0  inches,  two  were 
5.0  inches,  three  were  5.5  inches,  nine  were  6.O  inches,  eight 
were  6.5  inches,  twelve  were  7.0  inches,  nineteen  were  7.5 
inches,  thirty-two  were  8.0  inches,  forty  were  8.5  inches, 
sixty-seven  were  9.0  inches,  sixty-three  were  9.5  inches, 
thirty -eight  were  10  inches,  twenty-one  were  10.5  inches,  eight 
were  n.o  inches,  two  were  11.5  inches,  and  one  was  12.0 
inches  long.2 

1  By  a  "  random  sample  "  is  meant  a  sufficient  portion  of  the  whole,  taken  so 
much  at  random  as  to  fairly  represent  the  entire  crop,  or  "population,"  as  the 
technical  phrase  goes. 

2  Measurements  might  be  taken  at  quarter  inches  with  a  seemingly  higher 
degree  of  accuracy,  but  repeated  trials  show  that  the  same  final  results  follow 
whether  measurements  are  taken  at  the  quarter  inch  or  at  the  half  inch.    The  main 
point  is  that  the  numbers  shall  be  sufficient  and  that  the  sample  shall  be  repre- 
sentative.   Judgment  must  dictate  as  to  the  accuracy  of  the  sample,  but  the  num- 
ber depends  upon  the   degree   of  reliability  desired.    This  matter  will  be  fully 
discussed  under  the  subject  of  probable  error,  but  experience  shows  that  in  studies 
with  corn  excellent  results  can  be  had  with  from  200  to  300  ears,  and  very  fair 
results  may  generally  be  had  with  half  that  number. 


TYPE   AND   VARIABILITY  421 

Put  in  tabular  form  as  it  appears  in  actual  work  we  have  the 
folio vving  : 1 


Length  of  Ears, 
or  Value,—  V 

3.0     / 

No.  of  Ears,  or 
Frequency,  —y 

1 

3.5 

0 

4.0     / 

1 

4.5 

0 

5.0     // 

2 

5.5     /// 

3 

6.0     W///// 

9 

6.5     fW  '  /// 

8 

7.0    /W  /W  // 

12 

7.5     /W  M  /W  //// 

19 

8.0    IW  M  W/  M  M/  W/  // 

32 

85    /W/M/H//H//ft/M//H/ft{/  ' 

40 

9.0    MM/ti/MMMWm/tt/MMM/tt/// 

fi7 

9.5    M  M  M  M  M  /tt/  M  M  /%/  M  M  M  /// 

A3 

10.0    M  M  /tt/  /M  M  M  /%//// 

38 

105   IMLMJULM-L 

21 

11.0    A//// 

8 

11.5    // 

8     J 

12.0    / 

1 

Here  we  have  a  "  frequency  distribution  "  representing  the 
entire  "  population,"  or  crop,  and  as  it  lies  spread  out  before 
the  eye  a  glance  is  sufficient  to  afford  considerable  information 
as  to  the  prevailing  type. 

It  will  be  noted  at  once  that  there  are  more  ears  of  9  inches 
than  of  any  other  length,  and  that  the  distribution  decreases  in 
both  directions,  but  unequally,  from  this  highest  frequency. 

The  mode.  This  highest  frequency,  or  most  common  length, 
shows  clearly  what  is  the  prevailing  type  in  the  crop,  as  distinct 
from  the  selective  type  of  10  inches  in  the  seed  ear,  and  it  is 
held  by  statisticians  and  by  students  generally  to  be  the  best 
obtainable  single  expression  for  type.  When  it  is  ascertained, 

1  This  is  the  most  convenient  form  in  which  to  make  the  original  record.  A 
mark  is  made  for  every  individual  examined,  and  the  additions  are  readily  made. 


422 


TRANSMISSION 


therefore,  we  know  at  once  wJiat  is  the  natural  type1  of  the  race 
or  variety  so  far  as  the  character  in  question  is  concerned,  arjfl 
when  this  is  determined  for  a  number  of  important  characters  we 
shall  have  a  good  knowledge  of  the  racial  type  as  a  whole.  Thus 
we  might  obtain  the  mode  for  circumference,  number  of  rows, 
weight  of  ear,  color  of  grain,  per  cent  of  cob,  or  any  other  desired 
character,  and  having  done  so  a  typical  ear  of  this  variety  could 
be  definitely  described.  We  thus  arrive  at  an  accurate  idea  of 
type  in  a  general  population,  and  of  its  definite  measurement. 

The  empirical  and  the  theoretical  mode.  It  is  evident  by  in- 
spection of  the  frequency  table  that  if  measurements  had  been 
taken  at  the  quarter  inch,  or  some  less  fraction,  the  highest  fre- 
quency would  have  fallen  not  at  the  nine-inch  point  but  slightly 
above  it,  for  the  next  frequency  above  (63)  is  greater  than  the 
next  one  below  (40) ;  that  is  to  say,  the  mode  is  to  some  slight 
extent  dependent  upon  the  scheme  of  measurements  adopted. 

Any  scheme  expressed  in  numbers,  either  whole  or  fractional, 
is  of  course  by  nature  discontinuous,  and  the  mode  arising  from 
such  a  scheme  is  at  best  only  an  approximation.  It  is  therefore 
called  the  empirical  mode.  If  all  possible  values  were  repre- 
sented, however,  as  is  done  whenever  the  theoretical  curve  is 
plotted  corresponding  to  the  frequency  distribution,  such  a  con- 
tinuous curve  will  find  the  true  or,  as  it  is  called,  the  "  theoretical " 
mode.  It  is  necessary  to  recognize  this  distinction,  although 
in  practical  breeding  operations  the  empirical  mode  arising 
from  convenient  measurements  is  sufficiently  accurate. 

The  coefficient  of  mode,  or  modal  coefficient.2  It  is  not  enough 
simply  to  determine  which  value  has  the  highest  frequency, 
even  though  this  gives  us  the  type ;  we  desire  to  know  also 
what  proportion  of  all  the  individuals  tends  to  drop  into  the  type 

1  It  is  evident  that  the  frequency  distribution  and,  therefore,  the  type  of  an 
adult  population  is  something  different  from  that  which  was  born  into  the  race. 
What  that  may  have  been  we  can  never  know.    Many  individuals  did  not  survive, 
and  the  development  of  all  was  influenced  by  environment.    The  final  result  as 
represented  in  adult  individuals  is  all  we  can  consider. 

2  The  writer  has  never  seen  this  expression  used.    It  is  of  little  consequence  in 
general    evolution,  but   is  of   much   significance   in   thremmatology,  where   the 
breeder  desires  to  know  what  proportion  of  his  animals  or  plants  conform   to 
type.     I  have,  therefore,  taken  the  liberty  of  using  it,  as  here,  —  "  the  coefficient 
of  mode,  or  modal  coefficient." 


TYPE   AND   VARIABILITY  423 

of  the  race.  This  is  easily  determined  in  the  form  of  a  rate 
per  cent  by  dividing  the  highest  frequency  by  the  total  Dumber 
of  variates.1  The  highest  frequency  in  this  case  is  67,  which  is 
over  20  per  cent  (20.4  +)  of  the  total  number  of  ears  measured. 
This  we  call  its  modal  coefficient  because  it  indicates  the  per- 
centage of  the  total  population  that  conforms  to  type  in  respect 
to  this  character.  The  modal  coefficient  of  some  other  variety 
might  be  quite  different,  showing  that  a  higher  proportion  of 
one  variety  may  conform  to  type  than  of  another ;  or,  what  is 
the  same  thing,  that  one  variety  may  be  more  constant  and 
truer  to  type.  The  modal  coefficient,  therefore,  is  an  index  of 
relative  conformity  to  type,  a  valuable  bit  of  knowledge  for 
purposes  of  selection. 

Modal  coefficient  partly  dependent  upon  the  scheme  of  measure- 
ments adopted.  If  these  measurements  had  been  taken  to  the 
quarter  inch  there  would  have  been  twice  as  many  frequencies 
and  each  would  have  been  represented  by  correspondingly  fewer 
ears.  The  highest  frequency,  therefore,  would  have  been  not  67 
but  approximately  half  that  number,  —  33  or  thereabouts, — 
and  the  modal  coefficient  would  have  been  not  20  per  cent  but 
near  10  per  cent.  This  being  the  case,  modal  coefficients  are  not 
directly  comparable  except  when  arising  from  the  same  system 
of  measurements,  or  after  the  coefficient  has  been  divided  by 
the  width  of  the  class  ;  thus,  20  -f-  \  equals  10  -+-  |. 

For  the  purpose  of  comparing  the  variability  of  races  we  use 
the  "  coefficient  of  variability,"  to  be  described  later.  The  modal 
coefficient  is  chiefly  valuable  for  comparing  one  type  with 
another  within  the  race,  which  is  all  that  is  required  in  ordinary 
breeding. 

Practical  value  of  the  frequency  distribution,  the  mode,  and 
the  modal  coefficient.  The  practical  importance  of  the  informa- 
tion afforded  by  these  values  must  be  apparent.  By  means  of 
the  frequency  distribution  the  breeder  is  enabled  at  any  time, 
when  he  can  secure  sufficient  numbers,  to  spread  out  before  his 
eyes  a  good  and  fair  representation  of  the .  whole  population  of 
the  variety  or  race  he  is  breeding,  with  respect  to  any  character 
which  he  can  measure  or  accurately  estimate. 

1  Hy  variates  is  meant  the  individuals  measured  (in  this  case  327  ears). 


424 


TRANSMISSION 


When  he  has  ascertained  its  mode  he  knows  what  is  the 
naturaktype,  for  mode  indicates  type ;  and  he  then  knows  by 
how  much,  if  any,  it  differs  from  the  type  1  which  he  has  chosen 
as  the  standard  for  selection.  By  this  he  may  judge  whether 
and  to  what  extent  he  is  operating  at  variance  with  nature. 

The  mean.  There  is  still  another  conception  of  type  as  to 
this  distribution,  and  that  is  the  average,  or  "  mean  "  as  it  is 
technically  called.  It  will  be  noted-  that  the  dis- 
tribution does  not  decline  uniformly  both  above 
and  below  the  mode ;  that  is  to  say,  there  are 
six  values  below  and  only  three  above, — from 
which  we  conclude  that  the  average  length  of  ear 
is  somewhat  different  from  the  most  usual  length. 
By  multiplying  each  separate  length  by  the  num- 
ber of  ears  of  that  length  and  adding  the  products 
(or,  what  is  tne  same  thing,  adding  together  the 
lengths  of  all  the  ears)  and  then  dividing  by  the 
total  number  of  ears,  we  find  the  average,  or 
mean  length,  to  be  8.83—  inches. 

Accordingly  we  have  the  following  for  the  de- 
termination of  the  mean  2  :  Multiply  each  value 
by  its  frequency,  add  the  results,  and  divide  the 
sum  by  the  number  of  individuals  3  or  variates. 

Applying  this  principle  to  the  case  in  hand  we 
have  the  result  seen  in  the  accompanying  table  :  4 


3-o  x 

3-5  x 
4-o  x 

4-5  x 
5-o  x 

5-5  x 
6.0  x 
6.5  x 

7-O  X  12  = 

7.5  x  19=  142.5 
8.o  x  32  =  256.0 
8.5  x  4°  —  34°-° 
9-o  x  67  =  603.0 
9-5  x  63  =  598-5 
IO.Q  x  38  =  380.0 

10-5  X  21  —  220-5 

1 1. ox  8-  88.0 

II.5  X   2  =  23.0 
I2.O  X   I  =   12. 0 


327  2887.0 

2887.0-4-327=8.83-, 


*  It  is  customary  to  drop  off  extremely  outlying  values  in 
the  distribution,  but  evidently  in  this  case  if  very  large  num- 
bers had  been  taken  these  blanks  would  have  been  filled  ;  that  is,  ears  of  3.5  inches 
and  4.5  inches  would  have  been  found  ;  hence  all  values  are  included  here. 

L  Here  is  another  conception  of  type.  The  ideal  of  the  breeder,  which  he 
accepts  as  his  standard,  is  a  kind  of  economic  or  business  type,  quite  distinct 
from  the  biological  type  indicated  by  the  mode.  The  purpose  of  all  breeding  is 
to  bring  the  two  as  close  together  as  possible. 

2  By  "  mean  "  is  here  meant  the  arithmetical  average,  which  is  the  average  most 
commonly  accepted  and  the  symbol  of  which  is  M.    For  a  discussion  of  different 
averages,  see  Appendix. 

3  The  algebraic  formula  would  be  Af=  LliGLJ  1512,  in  which 

n 

fafi'-'fr  are  the  frequencies,   l\,  }'»•••  Vr  the  respective  values,  and  //  the 
number  of  individuals  measured. 

4  In  this  table   V  stands  for  values,  or  magnitudes,  —  in  this  case  length,  — 
and  f  stands  for  frequency,  or  the  number  of  varieties  (ears)  of  each  separate 
measurement.     The  whole  column  under  /is  technically  known  as  a  "frequency 


TYPE   AND   VARIABILITY 


425 


Here  we  have  a  third  valuation  for  type  (8.83—),  represent- 
ing the  average,  as  distinct  from  9  of  the  highest  frequency, 
or  most  usual  length,  and  both  distinct  from  the  10  inches  of 
the  ear  planted. 

Practical  use  of  the  mean.  The  mean  gives  a  good  average 
value  of  the  character,  and  establishes  the  practical  or  com- 
mercial value  of  a  race  or  variety,  for  it  shows  what  it  will  do 
on  the  average.  It  is  not  always,  however,  a  good  index  of  the 
prevailing  type,  for,  as  often  happens,  the  variety  with  the 
higher  mean  may  have  the  lower  mode.  Neither  is  the  mean 
always  a  good  index  of  conditions  ;  for  example,  in  a  population 
of  one  thousand  paupers  and  one  millionaire  the  mean  wealth 
is  fair,  but  the  type  is  clearly  that  of  the  pauper. 

Here  are  three  separate  and  very  definite  conceptions  of 
type:  (i)  the  ideal,  which  is  used  in  selecting  the  parentage; 
(2)  the  prevailing  type  as  represented  by  the  highest  frequency 
or  most  usual  length  (the  mode) ;  and  (3)  the  average  length  as 
represented  by  the  mean." 

These  three  conceptions  of  type  —  the  ideal  type  of  the 
parent,  the  prevailing  type  of  the  offspring,  and  the  general 
average  of  the  offspring  —  have  distinct  applications  to  the 
practical  affairs  of  breeding.1  The  breeder  of  pedigreed  stock 
is  interested  primarily  in  the  ideal  and  in  the  mode,  or  highest 
frequency,  while  the  general  farmer  who  multiplies  or  raises  it 
for  the  open  market  is  most  interested  in  its  mean,  or  average 
production. 

SECTION    II  —  VARIABILITY,   OR   DEVIATION 
FROM  TYPE 

Having  established  definite  distinctions  as  to  type,  the  student 
of  transmission  should  next  form  equally  clear  conceptions  as  to 
deviation  from  type,  commonly  known  as  variability.2 

distribution,"  representing  an  entire  race,  spoken  of  as  the  "population."  The 
heading  fV  means  the  products  of  the  values  (lengths)  multiplied  by  the  corre- 
sponding frequencies. 

1  It  is  to  be  noted  that  the  generation  to  which  the  selected  parent  belonged 
had  also  its  own  mode  and  mean,  which  may  have  been  quite  different  from  those 
of  the  offspring. 

2  The  term  "  variability  "  should  not  be  understood  as  expressing  departure 
in  the  sense  of  wandering  from  a  fixed  standard.    Students  sometimes  gain  the 


426  TRANSMISSION 

In  the  study  of  variability  it  is  worse  than  useless  to  study  a 
few  scattered  individuals  here  and  there.  What  we  seek  is  a 
measure  of  what  may  be  called  the  average  tendency  to  deviate 
from  type.  Some  individuals  deviate  but  little,  others  more, 
and  still  others  very  much,  and  we  seek  a  measure  of  this  non- 
conformity to  type.  To  find  this  we  must  study  groups  of  in- 
dividuals sufficiently  large  to  be  representative  of  their  race. 
This  brings  us  back  to  the  frequency  distribution  and  what  it 
can  teach  as  to  variability.1 

impression  that  if  the  law  of  heredity  were  infallible  all  offspring  would  be  of  a 
common  type,  and  that  any  departure  from  the  type  of  the  race,  variety,  or  breed 
is  to  be  regarded  as  by  so  much  a  failure  of  heredity  and  a  concession  to  variation. 

The  truth  is  that  all  transmission  is  heterogeneous  in  the  sense  that  the  indi- 
viduals of  any  race,  whether  parents  or  offspring,  belong  not  to  a  fixed  type  but 
to  a  frequency  distribution  similar  to  the  one  now  under  discussion.  The  idea  of 
type  thus  arises  out  of  the  distribution,  and  it  constitutes  a  convenient  base  from 
which  to  reckon  deviation. 

The  chief  conception  to  rest  in  the  mind  of  the  student  at  the  present  stage  of 
matters  is  that,  whatever  the  parentage,  the  offspring  will  constitute  a  distribution 
extending  through  a  considerable  range,  and  that  the  parent  itself  also  belonged 
and  was  drawn  from  some  portion  of  a  frequency  distribution  not  very  different 
from  that  of  the  race  in  general. 

Variability  is,  therefore,  not  the  opponent  of  heredity  but  its  inevitable 
accompaniment  in  transmission,  and  our  problem  is  to  devise  methods  of  accu- 
rately measuring  and  expressing  its  range  and  extent  in  any  particular  instance. 

1  No  apology  is  made  for  introducing  the  so-called  statistical  method  of  study 
at  this  point ;  first,  because  it  is  the  only  reliable  method  of  attacking  problems 
in  transmission,  and  second,  because  this  method  is  everywhere  coming  into  use 
among  careful  students.  The  reader  is  urged,  and  the  student  should  be  required, 
not  to  evade  this  portion  of  the  subject  because  the  method  of  treatment  may 
happen  to  be  unfamiliar.  On  the  other  hand,  he  is  urged  to  familiarize  himself 
not  only  with  the  method  of  work  but  with  the  point  of  view  involved.  If  he  will 
do  this,  both  variability  and  later  on  correlation  and  heredity  in  general  will  come 
to  have  a  new  meaning,  and  one  far  more  rational  and  comprehensive  than  the 
hazy  notions  evolved  from  the  unsystematic  study  of  isolated  individuals.  The 
principles  involved  are  for  the  most  part  simple,  and  in  this  elementary  treatise 
every  effort  will  be  made  to  treat  the  subject  from  the  standpoint  of  the  non- 
mathematical  reader. 

For  the  convenience  of  those  who  may  care  to  pursue  a  little  further  some  of 
the  more  strictly  mathematical  conceptions  involved,  an  Appendix  has  been  pre- 
pared by  Dr.  H.  L.  Rietz,  of  the  mathematical  department  of  the  University  of 
Illinois. 

The  statistical  method  of  study  of  problems  in  heredity,  as  distinct  from  the 
strictly  biological,  was  introduced  by  Dr.  Francis  Gallon  of  England  (see  Natural 
Inheritance,  1889),  and  afterward  much  extended  by  Karl  Pearson  and  others 
(see  especially  Grammar  of  Science  and  Philosophical  Transactions  of  the  Royal 
Society).  It  is  now  coming  into  such  common  use  that  a  quarterly  journal 


TYPE  AND   VARIABILITY 


427 


DEVIATION  OF  327  EARS 
OF  CORN  FROM  THEIR 
MEAN  LENGTH  OF 
8.83  INCHES 


Again  the  concrete  serves  well  as  a  medium  for  teaching  a 
principle.  In  this  connection  we  refer  once  more  to  our  distri- 
bution of  327  ears,  and  note  that  every  ear  in  the  lot  deviates 
somewhat  from  the  mean  of  8.83  inches.  The  range  and  extent 
of  this  deviation  are  shown  in  the  following  table,  column  D, 

The  practical  question  now  is  to  reduce 
this  column  of  deviations  to  a  single  ex- 
pression denoting  the  variability  of  the 
population  of  which  this  distribution  is 
representative.  Manifestly,  when  this  is 
done,  the  variability  of  this  distribution 
can  be  compared  directly  and  exactly  with 
that  of  any  other,  and  at  the  present  or 
any  future  time.  Two  methods  of  pro- 
cedure are  possible  in  thus  securing  a  kind 
of  general  expression  for  the  average 
amount  of  deviation,  giving  rise  to  two 
similar  but  slightly  different  values, 
namely,  the  average  deviation  and  the 
standard  deviation. 

The  average  deviation.  If  each  devi- 
ation (column  D)  represented  an  equal 
number  of  ears,  this  single  expression 
could  be  readily  derived  by  adding  the 
deviations  and  dividing  by  the  total 
number.  But  these  deviations  do  not 
represent  equal  numbers  of  ears.  The 
deviation  —5.83,  for  example,  represents  but  one  ear,  while  no 
less  than  twelve  ears  deviated  1.83  inches  below  the  mean  and 
two  deviated  2.67  inches  above,  with  others  unevenly  distributed. 

Manifestly  each  deviation  should  first  be  multiplied  by  the 
number  of  ears  involved,  as  in  the  succeeding  table  : x 

(Biometrikd)  is  devoted  to  the  reports  of  statistical  studies  in  evolution,  technically 
known  as  "  biometry." 

1  When  the  deviation  is  to  be  obtained  in  this  way  the  minus  sign  is  disregarded. 

*  D  indicates  the  deviation  of  the  several  groups  from  the  common  mean  of 
the  race,  8.83  inches.  Thus,  for  example,  the  first  ear  deviates  the  difference 
between  3  inches  and  8.83  inches,  or  5.83,  which,  being  below  the  mean,  is  written 
with  the  negative  sign  ;  also  the  21  ears  10.5  inches  long  deviate  10.5—8.83,  or  1.67 
inches  from  the  mean,  and  being  above  the  mean,  we  write  it  positive. 


V 

f 

/?* 

3-o 

I 

-5.83 

3-5 

o 

-  5-33 

4-o 

I 

-4.83 

4-5 

0 

-4-33 

5-° 

2 

-3-83 

5-5 

3 

-  3-33 

6.o 

9 

-  2.83 

.6-5 

8 

-2-33 

7-o 

12 

-1.83 

7-5 

19 

—  1.33 

8.o 

32 

-0.83 

8.5 

40 

-o-33 

9-o 

67 

0.17 

9-5 

63 

0.67 

IO.O 

38 

1.17 

10.5 

21 

1.67 

II.O 

8 

2.17 

"•5 

2 

2.67 

12.0 

I 

3-  17 

327 

428 


TRANSMISSION 


/     I> 

i  x  5.83 

0  x  5.33 

1  x  4-83 
o  x  4-33 

2  x  3.83 

3  x  3-33 

9  x  2.83 
8  x  2.33 

12  X  1.83 

19  x  1.33 
32  x  0.83 
40  x  0.33 
67  x  0.17 
63  x  0.67 
38  x  1.17 

21   X   1.67 

8  x  2.17 

2  X  2.67 

_}_  x  3-J7 
327 


Df 

=  5.83 
=  0.00 

=  4.83 

=    o.oo 

=  7.66 

=  9-99 
=  25-47 
=  18.64 
=  21.96 
=  25.27 
=  26.56 
=  13.20 

=  "-39 
=  42.21 
=  44.46 
=  35-°7 
=  !7-36 
=  5-34 

=_JLLZ- 
318.41 


The  result  of  this  calculation  is  that  the 
total  deviation  of  327  ears  from  their  average 
length  is  318.41  inches,  some  above  and  some 
below  the  mean.  If  now  we  divide  318.41  by 
327,  the  number  of  ears  involved,  we  have 
0.97+  inches,  which  is  a  good  expression  of 
the  average  deviation  of  this  particular  popu- 
lation. If  another  variety  should  give  a  larger 
quotient,  we  should  conclude  it  to  be  more 
variable.  In  this  manner  we  may  reduce  the 
variability  of  a  whole  population  to  a  single 
expression. 

Standard  deviation.  Mathematicians  have 
another  method  of  calculating  variability.  It 
differs  from  the  one  just  discussed  in  only  one 
detail ;  namely,  the  deviations  are  squared 
before  multiplication  by  their  respective  fre- 
quencies, as  in  the  table  which  follows  : 


V 

/ 

D 

n** 

D-  /t 

3-° 

I 

-  5-83 

33-9889 

33.9889 

3-5 

O 

-  5-33 

28.4089 

00.0000 

4.0 

I 

-4-83 

23.3289 

23.3289 

4-5 

O 

-  4-33 

18.7489 

00.0000 

5-° 

2 

-3-83 

14.6689 

29-3378 

3 

-  3-33 

11.0889 

33.2667 

60 

9 

-2.83 

8.0089 

72.0801 

6-5 

8 

-  2.33 

5.4289 

43-43  i  2 

7.0 

12 

-1.83 

3-3489 

40.1868 

7-5 

19 

1.7689 

33.6091 

8.0 

32 

-0.83 

0.6889 

22.0448 

8-5 

40 

-  o-33 

0.1089 

4.3560 

9.0 

67 

0.17 

0.0289 

1-9363 

9-5 

63 

0.67 

0.4489 

28.2807 

1  0.0 

38 

1.17 

1.3689 

52.0182 

10.5 

21 

1.67 

2.7889 

58.5669 

II.O 

8 

2.17 

4.7089 

37.6712 

"•5 

2 

2.67 

7.1289 

14.2578 

I2.O 

1 

10.0489 

10.0489 

327 

S  538.4103  \ 

*  The  column  marked  /**  is  secured  by  squaring  the  various  deviations,  thus 
eliminating  the  minus  sign.  For  example,  —  5.83  X  —  5.83  =  33.9889. 

t  The  column  marked  D^f  is  obtained  by  multiplying  the  squared  deviations 
each  by  its  respective  frequency.  For  example,  8.0089  x  9  —  72.0801. 

\  The  Greek  capital  sigma  (2)  is  the  usual  sign  of  summation  in  mathematics. 


TYPE   AND   VARIABILITY  429 

Dividing  538.4103  by  327  after  the  manner  of  finding  the 
average  deviation,  we  have  the  quotient  1.6465  ;  but  as  the 
deviations  have  all  been  squared  during  the  operation  it  is 
necessary  to  extract  the  square  root  of  this  number  in  order  to 
arrive  at  the  correct  value.  The  square  root  of  1.6465  is  1.28  +, 
and  this  is  the  so-called  standard  deviation  of  the  mathema- 
tician, the  universal  sign  for  which  is  the  Greek  letter,  small 
sigma  (a). 

Hence,  to  find  the  standard  deviation,  we  have  the  rule  :  Find 
the  deviation  of  each  frequency  from  the  mean ;  square  each 
deviation,  and  multiply  by  its  corresponding  frequency  ;  add  the 
products,  divide  by  the  total  number  of  variates,  and  extract 
the  square  root.1 

Shortening  the  method.  The  large  decimals  can  be  avoided, 
and  the  process  of  finding  both  the  mean  and  the  standard 
deviation  can  be  very  much  shortened,  by  assuming  as  a  mean 
the  nearest  probable  measurement  as  determined  by  inspection 
of  the  frequency  distribution,  and  afterward  making  a  suitable 
correction.  For  example,  in  the  present  instance,  we  should 
judge  by  inspection  that  the  mean  cannot  be  far  from  9.0.* 
This  we  infer  from  the  fact  that  the  distribution  reduces  both 
ways  from  this  point  and  quite  evenly.  Proceeding  with  this 
assumption,  denoting  our  "guess"  by  G  and  reckoning  devia- 
tion provisionally  from  this  point,  we  have  the  result  as  seen 
in  the  table  on  the  following  page. 

Considering  first  the  mean  :  In  column/(F—  G)  we  findxthat 
after  multiplying  the  deviations  from  our  assumed  mean  (9.0) 
by  their  respective  frequencies,  the  sum  of  the  negative  products 
(—  181.0)  exceeds  the  sum  of  the  positive  products  (125.0)  by 
56.0 ;  that  is,  the  algebraic  sum  of  the  products  is  —  56.0. 
Our  assumed  mean  is  therefore  too  high  by  the  amount  of 
-  56.0  -1-327!=  —  o.  171.  We  then  reduce  our  assumed  mean 

1  Expressed  in  symbols  the  formula  is  <r  —  \ _• 

H 

*  The  advantage  of  assuming  this  value  from  which  to  reckon  deviation  lies  in 
the  fact  that  it  is  exact  and  contains  but  one  decimal,  while  the  true  mean  has  at 
least  two  decimal  places,  making  relatively  large  numbers. 

t  We  divide  by  the  total  number  (327)  because  we  are  dealing  with  a  column 
of  products  arising  from  the  introduction  of  the  frequencies. 


430 


TRANSMISSION 


by   this   amount  (9.0  —  0.171=8.829)  and  arrive   at  the  true 
mean  8.83  — .* 

Considering  next  the  standard  deviation  :  In  column/(  V—  <7)2 
we  have  548.00  as  the  sum  of  the  products  of  the  several  fre- 
quencies into  their  respective  deviations  from  the  assumed  mean, 
derived  on  the  same  plan  as  when  working  from  the  true  mean 


ir 

/ 

V-G 

f(l'-G) 

(V-G? 

f(v-G? 

3-° 

I 

-6.0 

-    6.0 

36.OO 

36.00 

3-5 

O 

-  5-5 

0.0 

30^5 

00.00 

4.0 

I 

-  5-o 

-    5-o 

25.00 

25.00 

4-5 

O 

-  4-5 

o.o 

2O.25 

oo.oo 

5-° 

2 

-  4.0 

-    8.0 

1  6.00 

32.00 

5-5 

3 

-3-5 

-  10.5 

12.25 

36.75 

6.0 

9 

-  3-° 

-  27.0 

9.00 

81.00 

6.5 

8 

-  2-5 

—   20.0 

6.25 

50.00 

7.0 

12 

—  2.O 

-   24.0 

4.00 

48.00 

7-5 

*9 

-  i-5 

-   28.5 

2.25 

42.75 

8.0 

32 

-    1.0 

-  32.0 

I.OO 

32.00 

8.5 

40 

-o-5 

—   2O.O 

0.25 

IO.OO 

9.0 

67 

o.o 

o.o       —  181.0 

o.oo 

oo.oo 

9-5 

63 

o-5 

3!-5 

0.25 

15-75 

1  0.0 

33 

I.O 

38.0 

I.OO 

38.00 

10.5 

21 

«-5 

3'-5 

2.25 

47-25 

II.O 

8 

2.0 

16.0 

4.00 

32.00 

I'-S 

2 

2-5 

5.0 

6.25 

12.50 

I2.O 

I 

3-o 

3.0           125.0 

9.00 

9.00 

327 

Difference,  —  56.0 

S  548.00 

D.  Dividing  by  the  total  number  (327},  we  have  548.00  -^-,327  = 
1.6758,  corresponding  to  the  quotient  538.4103  -s-  327  =  1.6465 
of  the  previous  calculation  when  working  from  the  true  mean. 

The  correction  made  in  the  mean  was  — o.  171;  but  as  we  are 
now  dealing  with  second  powers  it  seems  but  natural  that  this 
amount  should  be  squared  before  it  can  be  taken  from  the  quo- 
tient 1.6758,  an  operation  that  can  be  fully  justified  by  strictly 
mathematical  proof.  The  square  of  — o. 1 71  is  0.029241,  or  0.0292 + . 

*  On  the  other  hand,  should  the  sum  of  the  positive  deviations  exceed  the  sum 
of  the  negative  deviations  it  would  indicate  that  our  assumed  value  is  too  small, 
and  we  should  add  the  correction  in  order  to  arrive  at  the  true  mean. 


TYPE  AND   VARIABILITY  431 

We  have  therefore  as  a  correction  on  account  of  the  true  mean 
1.6758  —  0.0292+  =  1.6466. 

This  agrees  very  nearly  with  the  value  1.6465  previously 
found,  but  this  shorter  method  is  the  more  accurate,  because 
fewer  decimals  have  been  lost.  The  square  root  of  1.6466  is 
1.28+,  the  standard  deviation  sought,  agreeing  perfectly  with 
the  former  value  and  derived  by  a  very  much  shorter  method. 

The  student  will  note  that  the  difference  in  the  two  methods 
is  essentially  this  :  in  the  latter  we  deal  only  with  deviations, 
while  in  the  former  entire  values  are  involved.  It  is  true  that 
deviations  are  taken  from  an  assumed  mean,  but  the  correction 
is  accurately  made,  and  the  whole  operation  can  be  carried 
forward  not  only  with  smaller  numbers  but  also  without  the 
loss  of  decimals  necessarily  involved  in  the  more  direct  but  far 
more  laborious  and  on  the  whole  less  exact  method  first  given. 
The  first  method  is  useful  for  expounding  the  principles  in- 
volved, but  the  later  is  far  preferable  for  actual  use,  not  only  on 
account  of  its  brevity,  but  on  account  of  its  increased  accuracy 
as  well. 

Average  deviation  and  standard  deviation  contrasted.  These 
two  expressions  for  variability  rest  upon  the  same  arithmetical 
principle,  but  the  latter  has  decided  mathematical  advantages 
over  the  former  for  many  purposes  and  is  the  one  universally 
used  by  mathematicians.  The  only  advantage  in  the  average 
deviation  lies  in  the  simpler  calculation,  as  neither  squares  nor 
roots  are  involved.  With  the  shortened  method  of  finding  the 
standard  deviation,  however,  this  advantage  is  slight. 

It  makes  little  difference  which  is  used  in  practice,  provided 
the  same  method  is  always  employed.  The  results  obtained  differ 
considerably  (0.97+  as  compared  with  1.28+).  The  standard 
deviation  is  always  larger  than  the  average  deviation  because  of 
the  squaring  of  the  several  deviations.  It  thus  exaggerates  the 
wider  departures  from  type  as  compared  with  the  methods 
employed  in  finding  the  average  deviation.  This  being  true, 
results  obtained  by  the  two  processes  can  never  be  compared ; 
that  is,  when  dealing  with  values  designed  to  express  variability 
we  must  always  know  whether  average  deviation  or  standard 
deviation  is  mpant. 


432  TRANSMISSION 

The  breeder  may  choose  either  method,  but  having  once 
chosen,  all  his  records  must  be  made  in  the  same  way.  In- 
asmuch as  the  standard  deviation  has  distinct  mathematical 
advantages  over  the  simple  average  deviation,  and  inasmuch  as 
it  is  the  one  commonly  employed  in  mathematical  literature,  it 
is  the  one  that  will  always  be  employed  in  this  text.  When, 
therefore,  a  measure  of  variability  is  mentioned  it  will  be  the 
standard  deviation  and  not  the  average  deviation  that  is  meant.1 

Meaning  of  standard  deviation.  The  standard  deviation  is  a 
good  measure  of  variability  for  the  character  in  question  and 
the  race  involved.  It  therefore  affords  a  reliable  basis  for  com- 
paring the  variability  of  one  race  with  that  of  another  as  to  the 
character  under  consideration,  or  of  one  character  with  that  of 
another  either  in  the  same  or  in  different  races. 

In  ascertaining  the  standard  deviation  the  mean,  or  average, 
of  the  race  was  taken  as  the  basis,  and  all  deviation  was  reckoned 
from  that.  It  is  manifest,  however,  that  if  the  mode  be  taken 
as  a  basis,  and  deviation  reckoned  from  this,  following  the  same 
methods  as  for  determining  the  standard  deviation,  a  somewhat 
different  value  will  result.  Whenever,  as  in  most  cases,  the 
mode  does  not  coincide  with  the  mean,  this  will  represent  the 
deviation  from  the  prevailing  type,  which  is  often  of  more  prac- 
tical importance  to  the  breeder  than  the  deviation  just  described, 
especially  to  the  breeder  who  proposes  to  deal  with  individuals 
selected  with  reference  not  to  the  mean  but  to  the  prevailing 
type. 

In  the  same  manner  the  breeder  may  calculate  the  deviation 
from  his  own  ideal  type  or  standard  and  in  this  way  assess  the 
deviation,  not  from  the  present  mean  or  type  but  from  the  one 
he  hopes  to  establish.  In  this  way  he  is  able  to  keep  accurately 
informed  from  year  to  year  as  to  the  progress  he  is  making  and 
the  degree  of  success  that  is  following  his  selections. 

The  writer  has  never  seen  either  of  these  determinations 
used,  but  they  are  especially  valuable  to  the  breeder  who  desires 
to  know  how  a  certain  variety  deviates  on  the  average  from  its 

1  In  the  section  on  "  Probability  Curve  "  (Appendix)  it  will  be  shown  that  the 
standard  deviation  is  on  the  whole  preferable  from  the  purely  mathematical 
standpoint. 


TYPE  AND  VARIABILITY 


433 


own  type  or  even  from  his  standard  of  selection,  as  well  as  to 
know  how  it  deviates  from  its  own  mean. 

I  have  therefore  recommended  their  use,  calling  the  one 
deviation  from  mode  and  the  other  deviation  from  standard, 
and  earnestly  suggest  their  constant  employment  by  the  breeder 
as  a  means  of  acquainting  himself  with  the  true  nature  of  the 
variety  he  is  attempting  to  improve ;  for  improvement  consists 
often  in  changing  the  type  as  well  as  in  bringing  a  larger  propor- 
tion of  the  population  to  conform  either  to  the  natural  or  to  the 
accepted  standard.1  To  do  this  he  should  make  these  determina- 
tions year  by  year,  and  keep  the  results  as  a  history  of  the  vari- 
ety or  breed  as  it  behaves  with  him  under  selection. 

Practical  meaning  of  standard  deviation.  Inasmuch  as  the 
standard  deviation  is  an  index  of  variability  whether  from  mean 
or  from  type,  it  expresses  accurately  the  tendency  of  the  variety 
to  wander,  so  far  as  the  character  in  question  is  concerned.  It 
affords,  therefore,  a  basis  of  comparison  of  one  variety  with 
another,  or  with  itself  at  some  future  time.  However,  one 
standard  deviation  ordinarily  cannot  be  compared  directly  with 
another  for  two  reasons  :  first,  one  mean  may  be  very  much 
larger  than  the  other ;  and  second,  the  two  may  be  of  entirely 
different  units,  as  inches  and  pounds,  in  which  case  direct 
comparison  is  impossible. 

Coefficient  of  variability.  We  seek,  therefore,  an  abstract 
expression  combining  the  idea  both  of  standard  deviation  and 
of  type.  Such  an  expression  is  known  as  the  "  coefficient  of  vari- 
ability," and  is  found  as  follows  :  Divide  the  standard  deviation 
by  the  mean  as  a  base,  and  the  result  will  be  an  excellent  index 
of  variability  appearing  in  the  form  of  a  rate  per  cent.2 

Thus,  for  the  case  in  question,  we  have  1.28  -s-  8.83  =  0.145, 
indicating  the  variability  of  this  population  to  be  over  14.5  per 
cent  of  its  own  mean.  Here  we  have  a  mathematical  expression 
for  comparing  variability  on  a  perfectly  abstract  basis,  and  by 
this  means  we  can  compare  the  variability  of  this  population 

1  "  Standard,"  as  here  used,  refers  to  the  scale  of  points,  or  that  which  the 
breeder  is  trying  to  establish.  It  is  his  standard  for  selection. 

standard  deviation         <r 

-  The  formula  is  C  = or  — . 

mean  M 


434  TRANSMISSION 

with  that  of  any  other  race,  plant  or  animal,  and  for  any  charac- 
ter of  which  accurate  measurements  can  be  taken  and  a  fre- 
quency distribution  be  constructed.1 

Practical  application  of  the  coefficient  of  variability.  The 
value  of  this  term  lies  in  the  fact  that  it  affords  an  accurate 
means  of  comparing  directly  the  variability  of  one  frequency 
distribution  with  that  of  another,  no  matter  what  the  character,  - 
whether  in  the  same  or  different  individuals,  or  between  similar 
or  unlike  species.  Thus,  by  this  means  we  may  compare  the  vari- 
ability of  the  length  of  an  ear  of  corn  with  that  of  its  weight ; 
the  variability  of  its  circumference  with,  that  of  its  number  of 
rows,  or  with  that  of  any  other  measurable  character. 

We  can  also,  in  this  way,  compare  the  variability  of  ears  of 
corn  with  that  of  their  stalks  ;  with  that  of  the  length  of  horse's 
legs,  of  what  they  can  pull,  or  of  the  rate  at  which  they  can 
travel ;  with  that  of  the  height  of  men,  their  weight,  length  of 
arms,  measurements  of  the  head,  —  indeed,  with  that  of  any 
object,  living  or  non-living,  that  possesses  variable  characters 
that  can  be  accurately  measured,  whether  by  feet,  inches, 
pounds,  or  by  any  other  unit  that  can  be  devised.2 

By  means  of  this  coefficient  the  breeder  may  not  only  ascertain 
whether  one  character  is  more  variable  than  another,  but  by 
taking  this  coefficient  frequently,  as  annually  for  the  same  variety 
or  under  different  conditions,  he  can  know  the  variability  of  the 
same  character  as  influenced  by  time  or  circumstances. 

In  general  these  determinations  enable  the  breeder  to  know 
which  way  his  varieties  are  drifting,  or  whether  they  are  standing 

1  Clearly,  if  the  mode  or  the  standard  of  selection  has  been  used  as  a  base  in 
calculating  the  deviation,  then  the  same  value  should  be  used  as  a  base  in  calcu- 
lating the  coefficient ;  thus  it  is  possible  to  secure  a  coefficient  of  variability  from 
any  desired  type  as  well  as  from  the  mean. 

2  The  coefficient  of  variability  has  been  worked  out  for  a  large  number  of 
characters  in  man,  as  is  shown  in  the  following  table  (see  Vernon,  Variation  in 
Animals  and  Plants,  p.  24). 

Nose  length 9.49  Head  breadth 2.78 

Nose  breadth 7.57  Upper  arm  length 6.50 

Nose  height 15.20  Forearm  length 3.85 

Forehead  height 10.40  Upper  leg  length 5.00 

Under  jaw  length 4.81  Lower  leg  length 5.04 

Mouth  breadth 5.18  Foot  length 5.92 

Head  length 2.44 


TYPE  AND  VARIABILITY  435 

still  in  spite  of  vigorous  selection ;  whether  in  his  selection  he 
is  operating  with  or  against  nature ;  whether  the  type  is  becom- 
ing a  little  more  "  fixed  "  or  whether  the  tendency  is  more  and 
more  to  scatter ;  whether  the  mean  or  general  average  of  excel- 
lence is  approaching  or  receding  from  the  desired  type  ;  whether, 
as  time  passes,  variability  is  lessened  or  increased ;  whether,  as 
the  result  of  selection,  new  values  are  coming  in  at  the  upper 
end.  In  short,  by  these  calculations  he  may  know  whether  he  is 
making  real  progress,  or  is  only  dabbling  in  the  whirl  of  vari- 
ability that  is  inevitable  with  all  living  things,  without  influ- 
encing at  all  the  trend  of  the  race.  It  is  needless  to  say  that 
much  of  this  latter  sort  of  ineffective  breeding  is  going  on  all 
about  us  everywhere.  The  statistical  method  is  the  only  known 
method  of  securing  accurate  knowledge  of  type  and  variability  ; 
for  type  is  not  simply  what  we  desire,  but  it  is  what  we  actually 
get,  and  any  breeder  is  working  in  the  dark  who  does  not  know 
the  real  nature  of  the  whole  population  of  the  race  he  breeds. 

SECTION   III  —  PRACTICAL  HINTS  ON  THE  TAKING  AND 
GROUPING  OF  MEASUREMENTS 

It  is  highly  improbable  that,  in  measuring  any  part  of  an 
organism,  a  perfectly  accurate  measure  is  obtained.  It  may  be 
very  easy  to  measure  the  length  of  an  object  accurately  to  i  inch, 
or  to  o.i  inch,  or  even  to  o.oi  inch,  if  the  ruler  is  sufficiently 
accurate ;  but  finally,  in  trying  to  measure  to  as  high  a  degree 
of  accuracy  as  possible,  we  come  to  a  point  where  our  ruler 
fails  us.  Again,  the  object  measured  may  be  of  such  a  nature 
that  it  is  futile  to  try  to  take  measurements  beyond  a  certain 
degree  of  accuracy.  For  instance,  it  would  be  useless  to  try  to 
measure  the  length  of  an  ear  of  corn  to  o.oi  inch.  Similarly,  in 
weighing  substances,  it  is  possible  with  a  good  balance  to  take 
measurements  to  ounces  or  to  tenths  of  milligrams  if  extreme 
accuracy  were  demanded  ;  but  finally,  in  striving  after  accuracy, 
the  balance  fails  us,  and  we  must  grant  that  it  is  highly  improb* 
able  that  the  weight  which  we  record  is  perfectly  accurate. 

While  we  thus  see  that  we  cannot  attain  absolute  accuracy  in 
any  measurements,  yet  thremmatology  is  no  exceptional  field  in 


436  TRANSMISSION 

this  respect,  and  experience  has  shown  that  measurements  can  be 
easily  taken  of  sufficient  accuracy  to  insure  very  reliable  results. 

For  obtaining  the  frequency  distribution  of  a  population  with 
respect  to  some  measurable  character,  it  is  impracticable  to  lay 
down  specific  rules  in  regard  to  the  accuracy  of  measurements. 
This  must  be  settled  largely  by  experience  and  common  sense. 
It  may,  however,  be  said  here  that  in  measuring  a  large  popu- 
lation, under  the  free  action  of  the  laws  of  probability,  substan- 
tially as  many  measurements  will  be  taken  too  large  as  are 
taken  too  small.  Hence  slight  errors  in  measurements  do  not 
appreciably  disturb  the  mean  and  variability  of  the  population, 
because  they  tend  to  offset  each  other. 

Scheme  of  measurement.  Reverting  to  the  frequency  dis- 
tribution obtained  from  measurements  of  corn,  it  will  be  noted 
that  this  population  is  distributed  in  classes  or  groups  which 
differ  by  a  half  inch  in  length.  For  the  purpose  of  forming  this 
frequency  table  there  would  then  be  no  object  in  taking  the 
measurements  closer  than  the  nearest  half  inch.  This  raises  the 
question  of  the  inclusiveness  of  a  class  in  grouping  a  population  ; 
that  is,  Should  these  measurements  have  been  taken  at  the 
quarter  inch  or  perhaps  at  the  even  inch  ?  Here,  again,  no  hard 
and  fast  rule  can  be  laid  down ;  but  it  may  be  said  that  in 
general,  and  for  the  best  results,  the  class  range  should  be  made 
just  large  enough  for  some  variates  to  appear  in  each  class, 
except,  possibly,  in  a  few  near  the  extremes  of  the  range  of 
variability  when  the  total  population  is  not  very  large. 

Sometimes  the  best  unit  for  measurement  and  grouping 
will  be  evident,  but  frequently  some  preliminary  work  is  neces- 
sary in  order  to  decide  it.  For  example,  in  beginning  the 
statistical  work  with  corn  we  at  first  took  measurements  to  the 
quarter  inch,  with  groupings  accordingly,  but  found  no  results 
different,  either  as  to  mean  or  variability,  from  those  obtained 
when  measurements  were  taken  to  the  half  inch,  and  but  slightly 
different  from  those  taken  at  the  even  inch.  Accordingly  we 
are  using  the  half-inch  measurements  for  extreme  accuracy  and 
the  even  inch  for  rougher  work. 

Much  judgment  must  be  used  in  deciding  upon  the  scheme 
of  measurements  to  be  adopted  and  the  groupings  to  be  made. 


TYPE  AND   VARIABILITY  437 

If  the  unit  of  measurement  be  large,  say  two  inches  for  corn, 
the  individual  values  will  not  be  accurate  ;  the  groups  will  be 
large,  but  so  far  apart  that  the  empirical  mode  will  have  but 
little  meaning.  If,  on  the  other  hand,  the  units  of  measure  be 
too  minute,  say  tenths  of  inches,  the  work  of  calculation  will 
be  vastly  increased,  and  while  the  empirical  mode  will  be  more 
accurate,  yet  the  distribution  will  not  be  "  smooth,"  as  the 
technical  phrase  goes  ;  that  is,  some  of  the  groups  near  the 
extremes  may  not  be  filled. 

The  scheme  must  be  so  chosen  and  the  groupings  so  made  as 
to  furnish  a  uniform  distribution,  with  fairly  smooth  results 
when  the  frequency  is  platted  in  the  form  of  a  curve.  The 
method  of  platting  frequency  distributions  and  dealing  with 
them  as  "  curves  of  frequency  "  will  be  shown  in  the  Appendix.1 


SECTION  IV  — PROBABLE  ERROR 

Mention  has  already  been  made  of  certain  inaccuracies  in 
measurements  and  groupings  of  a  population.  Attention  is  now 
called  to  another  source  of  error  which  arises  from  using  a 
limited  number  to  represent  the  total  population.  From  all 
these  sources  slight  errors  are  inevitable.  We  have  no  means  of 
determining  the  exact  error,  but  after  the  work  has  been  done  we 
may  find  a  measure  of  accuracy.  This  measure  of  accuracy  is 
called  the  "  probable  error." 

Whatever  the  source  of  error,  the  exact  discrepancy  in  a 
result  which  depends  upon  measurements  can  never  be  ascer- 
tained. However,  the  so-called  "  probable  error"  does  give  a 
measure  of  accuracy  which  indicates  whether  we  should  expect 
a  large  or  small  error  in  a  determined  value.  In  other  words,  it 
indicates  the  degree  of  confidence  which  we  should  place  in 
results  obtained  by  statistical  methods. 

1  In  general  this  may  be  done  by  laying  off  the  measurements,  as  inches,  half 
inches,  pounds,  etc.,  on  a  horizontal  line,  and  the  numbers  of  individuals  in  the 
distribution  as  verticals,  connecting  the  points  by  a  continuous  curve.  As  num- 
bers differ  greatly  in  different  cases,  it  is  best  to  reduce  them  all  to  the  basis  of 
100,  and  express  all  values  in  percentages.  If  this  is  done,  then  all  curves  of  the 
same  measurement  are  comparable. 


438  TRANSMISSION 

The  real  nature  of  probable  error  and  the  methods  for 
deducing  the  formulas  for  its  calculation  will  be  covered  in 
the  Appendix,  which  is  devoted  especially  to  mathematical 
methods  and  conceptions,  but  enough  should  here  be  said  to 
give  the  student  an  intelligent  idea  of  what  is  meant  by  probable 
error  and  to  acquaint  him  with  the  bare  formulas  for  its  calcu- 
lation as  to  the  values  here  under  discussion. 

The  probable  error  (denoted  by  ±  E)  is  a  pair  of  divergencies 
lying  one  above  and  the  other  below  the  value  determined,  and 
of  which  we  can  say  with  confidence  that  there  is  an  even  chance 
that  the  true  value  lies  between  these  limits.1  These  numbers 
are  numerically  equal,  but  one  is  regarded  as  plus,  the  other  as 
minus  (±^),  and  the  two  define  a  range  within  which,  out  of  a 
very  large  number  of  determinations,  at  least  half  the  true  values 
would  be  found.  This  being  the  case,  we  may  say  of  any  single 
determination  that  the  chances  are  even  that  any  error  involved 
will  not  fall  outside  the  limits  set  by  ±  E.  It  is  obvious,  there- 
fore, that  the  smaller  the  probable  error  the  narrower  this  range, 
the  greater  confidence  we  should  place  in  our  determination,  and 
the  smaller  are  the  chances  of  a  large  error  having  been  made. 

The  expression  "  probable  error"  may  be  misleading.  It  is 
not,  as  might  be  supposed  from  the  words,  the  most  probable 
error.  The  most  probable  value  is  our  determination  and  the 
most  probable  error  is  zero.  Neither  does  the  probable  error 
fix  the  limits  of  error,  but  it  is  an  extremely  good  measure  of 
accuracy  in  that  it  fixes  a  range  above  and  below  the  determined 
value  such  that  the  chances  are  even  that  the  true  value  lies 
within  this  range. 

Thus,  if  a  series  of  calculations  results  in  a  final  number  27.4, 
with  a  probable  error  of  ±.12,  it  means  that  out  of  a  great 
number  of  cases  the  true  value  of  one  half  will  lie  between 
27.52  (27.4  +  . 1 2)  and  27.28  (27.4  — .12). 

If  another  calculation  involving  larger  numbers  or  more  ac- 
curate methods  should  result  in  the  same  value,  27.4,  but  a 
probable  error  of  only  ±  .04,  then  the  true  value  has  an  even 
chance  of  lying  between  27.44  and  27.36,  which  is  a  very 

1  There  is,  of  course,  also  an  even  chance  that  the  true  value  lies  outside  the 
same  limits. 


TYPE  AND   VARIABILITY 


439 


narrow  margin,  giving  us  much  confidence  in  the  determination, 
with  only  a  small  chance  of  being  wide  of  the  truth. 

Of  course  the  error  in  a  determination  has  also  an  even 
chance  of  lying  outside  the  limits  set  by  the  probable  error  (E), 
but  the  following  table  will  show  that  it  is  very  unlikely  that 
the  error  is  many  times  as  great  as  E.  Thus  the  chances  that 
the  true  value  lies  within  the  range  set  by  ±E,  ±  2  E,  etc.,  are 
as  follows  : 1 

±  E  the  chances  are  even 
±  2  E  the  chances  are  4.5  to  i 
±  3  £"the  chances  are  21  to  i 
±  4  E  the  chances  are  142  to  i 
±  5  E  the  chances  are  1310  to  i 
±  6  E  the  chances  are  19,200  to  i 
±  7  E  the  chances  are  420,000  to  i 
±  8  -£"  the  chances  are  1 7,000,000  to  i 
±  9  E  the  chances  are  about  1,000,000,000  to  i 

It  is  extremely  improbable,  therefore,  that  an  error  will  be 
many  times  as  large  as  the  probable  error.  For  instance,  it  is 
practically  certain  that  the  error  is  not  as  large  as  9  E,  since 
the  table  shows  that  the  chances  are  about  a  billion  to  one  in 
favor  of  its  being  smaller  than  9  E. 

Thus  by  giving,  along  with  any  result,  the  calculated  probable 
error,  the  reader  may  know  what  degree  of  confidence  is  to  be 
placed  in  the  results. 

For  a  graphic  illustration  of  the  meaning  of  ±  E,  suppose  in 
the  following  figure  the  line  AB  represents  our  determination, 
and  the  lines  ab  and  a'b'  the  location  of  -f-  E  and  —E. 


*B' 

Now  this  means  that  if  AB  is  not  the  true  location  of  the  value 
in  question,  the  chances  are  even  that  this  location  is  not  outside 
the  limits  set  by  the  lines  ab  and  a'b'  representing  ±  E. 

1  C.  B.  Davenport,  Statistical  Methods,  p.  14. 


440  TRANSMISSION 

If  now  we  set  other  lines  like  the  following  at  ±  2 
ai   a  A  a1  a2 


*!   b  B  V  P 

then  we  know  from  the  table  that  the  chances  are  4.5  to  I 
that  the  true  position  of  AB  is  not  outside  the  lines  a1l^1  and  a2lP, 
each  removed  twice  the  probable  error  from  the  determination. 
Probable  error  of  mean.  The  probable  error  of  the  mean  is 
based  upon  the  standard  deviation,  as  we  notice  by  the  following 
formula  : l  standard  deviation 

^nean  =  ±  0.6745        /  ,  ,  . 

Vnumber  of  variates 
or  EM  =  db  0.6745  ~~/=' 

Substituting  for  the  case  in  hand,  we  have 

1.28 


V327 

The  student  cannot  fail  to  notice  the  overwhelming  influence 
of  numbers  in  controlling  the  value  of  E,  or  to  realize  that  if 
the  number  of  determinations  should  become  infinite,  E  would 
become  zero. 

Probable  error  of  standard  deviation.  According  to  methods 
of  deduction,  to  be  discussed  later,  the  probable  error  of  any 
determination  for  standard  deviation  is  found  by  the  follow- 
ing process  :  divide  the  standard  deviation  by  the  square  root 
of  twice  the  number  of  variates  and  multiply  the  result  by 


In  the  case  in  point  we  have  1.28  as  the  standard  deviation 
with  327  variates.    Substituting  these  numbers  in  the  formula, 

we  have  1<2g 

E^  =  ±  0.6745  =  ±  0.034  — . 

V2  x  327 

1  See  C.  B.  Davenport,  Statistical  Methods,  p.  15.    The  method  by  which  the 
constant  0.6745  is  obtained  will  be  explained  in  the  Appendix. 

2  The  formula  for  probable  error  of  standard  deviation  is 

Eff  =  ±0.6745-^. 


v  2  n 
See  C.  B.  Davenport,  Statistical  Methods,  p.  16. 


TYPE  AND   VARIABILITY 


441 


If  another  distribution  should  give  a  smaller  E,  we  should  con- 
clude that  more  confidence  could  be  reposed  in  this  second 
determination  than  in  the  first. 

Obviously  ±£  will  decrease  as  the  standard  deviation  de- 
creases or  as  the  numbers  examined  increase  (see  formula).  Our 
numbers  are  relatively  small  (327)  and  our  probable  error  is 
relatively  high,  though  it  constitutes  but  an  insignificant  frac- 
tion of  the  determination  (1.28). 

Probable  error  of  coefficient  of  variability.  When  the  coeffi- 
cient of  variability  (C)  is  small  (10  per  cent  or  less)  its  probable 
error  is  found  by  dividing  the  coefficient  of  variability  by  the 
square  root  of  twice  the  number  of  variates  and  multiplying  by 
±  0.6745  ;  that  is,  by  the  same  formula  as  the  one  just  given, 
only  substituting  coefficient  of  variability  for  standard  devia- 
tion.1 When  the  coefficient  is  larger  than  10  per  cent  we  use 
a  slightly  more  complicated  formula.2 

Since  the  variability  in  question  (14.5)  is  greater  than  10  per 
cent  we  employ  the  more  extended  formula  and  obtain  the 
following  : 


c=±  0.6745 


The  student  will  find  on  trial  that  for  these  values  the  two 
methods  give  results  but  slightly  different. 

Deviation  and  probable  error  illustrated.  This  whole  matter 
of  deviation  and  probable  error  is  well  illustrated  in  shooting 
at  a  mark.  Some  of  the  shots  will  strike  the  bull's-eye  and 
others  will  strike  at  various  distances  from  the  center,  some 
going  wild.  Obviously  the  better  the  shooting  the  closer  will 
the  shots  be  clustered  about  the  bull's-eye.  The  distance  of 
each  shot  from  the  center  would  be  its  deviation  from  the 
mark  and  the  mean  of  all  the  deviations  of  the  marksman  A 
would  represent  the  average  of  his  deviations. 

f* 

1  Formula  Ec  =  ±  0.6745  —  —  • 


=  ±  0.6745  —  —  I  i  +  2  /—  J       .      See   C.   B.    Davenport,    Statistical 
Methods,  p.  1  6.         ^  L 


442 


TRANSMISSION 


If  a  circle  be  drawn  about  the  center  with  a  radius  equal  to 
the  average  deviation  of  A,  this  circle  will  fairly  well  represent 
his  marksmanship ;  that  is  to  say,  the  average  distance  of  all  his 
shots  from  the  center  is  the  same  as  if  they  all  lay  on  this  circle. 
If  the  marksmanship  of  B  is  not  so  good  as  that  of  A,  his  average 
is  greater  and  the  circle  correspondingly  larger.1 

Now  neither  of  these  circles  is  an  absolute  index  of  the  marks- 
manship of  either  A  or  B,  unless  an  infinite  number  of  shots 
has  been  made ;  that  is  to  say,  if  only  a  few  shots  have  been 
fired,  the  probability  of  error  is  great  if  we  assume  these  circles 
to  be  fully  representative  of  the  marksmanship,  because  there 
is  practical  certainty  that  succeeding  shots  will  be  either  better 
or  worse  ;  indeed,  there  is  always  a  chance  that  the  next  may  be 
a  lucky  shot  and  lower  the  deviation,  or  a  wild  one  and  raise  it. 

We  should  therefore  conceive  of  two  other  circles  lying 
neighbor  to  each  of  those  representing  the  calculated  deviations. 
These  are  represented  in  the  cut  by  the  light-line  circles  and 
give  a  graphic  meaning  to  the  probable  error.  They  are  drawn 
so  that  if  the  heavy  circles  do  not  accurately  represent  A's  and 
B's  marksmanship  then  the  chances  are  even  that  the  true 
position  of  the  circle  representing  A's  marksmanship,  for  exam- 
ple, lies  somewhere  between  the  light  lines  representing  the 
probable  error  of  the  computation.  The  chances  are  of  course 
also  even  that  it  lies  beyond  these  limits,  either  within  or  outside. 
Obviously,  the  smaller  the  probable  error  the  greater  the  confi- 
dence to  be  placed  in  the  calculated  deviation.  The  student  is 
cautioned  here  that  in  this  illustration  the  "  probable  error" 
refers  not  to  A's  or  B's  failure  to  hit  the  target,  but  to  our 

1  The  question  may  be  raised  as  to  whether  there  is  not  a  better  measure  of 
marksmanship  than  the  average  departure  of  the  shots  from  the  bull's-eye.  For 
instance,  with  the  bull's-eye  as  a  center,  we  may  describe  circles  through  each  of 
the  shots  of  A,  and  construct  a  circle  with  the  average  area  of  these  circles  for 
its  "area.  This  circle  may  then  be  selected  as  a  measure  of  A's  marksmanship 
instead  of  the  circle  above  discussed.  The  radius  of  this  circle  can  be  obtained 
by  taking  the  square  root  of  the  mean  square  of  the  deviations  from  the  bull's- 
eye.  It  is  not  important  for  us  to  discuss  here  the  relative  merits  of  these  two 
methods  of  measuring  marksmanship,  but  it  is  important  that  we  recognize  that 
the  method  explained  in  the  text  is  based  upon  what  we  may  well  call  "  average 
deviation  from  an  ideal,"  while  that  suggested  in  this  footnote  may  well  1;e  called 
"  standard  deviation  from  an  ideal." 


TYPE   AND  VARIABILITY 


443 


calculation  in  assuming  the  circles  to  represent  the  deviation  of 
each,  when  only  a  limited  number  of  shots  had  been  fired. 

It  is  this  deviation  and  not  our  probable  error  that  is  to  be 
taken  as  expressing  error  in  marksmanship,  for  with  an  infinite 
number  of  shots  our  E  would  disappear,  but  the  error  in  marks- 
manship or  the  deviation  of  A  or  B  would  never  disappear.  With 
infinity  it  would  have  an  exact  and  fixed  value,with  E  =  o. 

It  is  obvious  that  the  deviations  above  alluded  to  are  devia- 
tions from  an  "  ideal  "  (the  center  of  the  target)  which  is  compar- 
able to  the  selection  type  in  practi- 
cal breeding.  It  is  obvious,  too, 
that  these  heavy  circles  represent 
the  means  of  all  the  shots  fired  by 
the  two  marksmen,  but  they  do  not 
represent  their  distribution.  That 
is  to  say,  A,  for  example,  might 
have  put  most  of  his  shots,  or  all 
of  them  for  that  matter,  at  a  uni- 
form distance  from  the  bull's-eye, 
none  hitting  the  center  and  none 
going  wild;  in  other  words,  his 
shooting  might  have  been  very 
uniform,  but  neither  very  good 
nor  very  bad,  owing  either  to  bad 
marksmanship  or  to  a  badly  sighted 
gun.  Now  it  is  conceivable  that 
another  marksman,  C,  should  succeed  in  making  an  average 
identical  with  that  of  A,  but  in  a  very  different  manner,  —  some 
of  the  shots  hitting  the  bull's-eye  and  some  going  wild.  These 
two  men,  then,  do  shooting  of  an  entirely  different  class  the  one 
from  the  other,  that  is,  make  a  very  different  distribution  even 
though  they  win  the  same  mean.  If  now,  from  this  mean  (repre- 
sented by  the  heavy  circles),  we  calculate  standard  deviation 
with  respect  to  all  the  shots  fired,  we  then  have  a  conception  of 
deviation  corresponding  exactly  to  that  of  the  ordinary  standard 
deviation ;  namely,  deviation  from  the  mean  of  all  the  variates. 
Thus  we  illustrate  both  deviation  from  mean  and  deviation  from 
an  ideal,  together  with  the  probable  error  involved. 


eB 


FIG.  44.  Let  the  heavy  lines  A  and 
B  represent  the  calculated  marks- 
manship of  A  and  B  respectively ; 
then  the  light  lines  peA  and  peB 
will  represent  the  probable  errors 
in  the  assumption  that  lines  A  and 
B  represent  truly  the  marksman- 
ship of  A  and  B 


444 


TRANSMISSION 


SECTION    V  —  COMPARATIVE     TYPE     AND     VARIABILITY 

FOR  DIFFERENT  CHARACTERS  IN  THE  SAME 

POPULATION 

If  a  variety  of  characters  in  the  same  population  be  critically 
studied  it  will  be  found  that  each  has  its  own  type  and  variability. 
For  example,  in  the  population  arising  from  the  ten-inch  ears 
already  discussed  it  was  found  that  other  characters  varied  as 
follows  : 

TYPE  AND  VARIABILITY  FOR  FOUR  CHARACTERS  OF  CORN  GROWN  FROM 
SEED  EARS  TEN  INCHES  LONG 


MEAN,  INCHES 
OR  OUNCES 

STANDARD  DEVIA- 
TION, INCHES  OR 
OUNCES 

COEFFICIENT  OF 
VARIABILITY, 
PER  CENT 

Length  of  ear 

8  829  ±  o  048 

I  287  -4-  o  O7J. 

14  57  -4-  O  7Q 

Circumference  of  ear  .  . 
Weight  of  ear  ..... 
Number  of  rows  .... 

7.047  ±  0.021 
12.75     ±0.12 

20.09    ±  o.  1  1 

0.568  ±  O.OI4 
3.163  ±  O.O86 
2.82O  ±  0.071 

i^oo  ^  ^-jy 

8.O6  ±  O.22 

24.82  ±  0.68 
14-03  ±  o-39 

From  this  we  see  that  each  separate  character  takes  its  own 
type  and  variability.  For  example,  corn  is  much  more  variable 
as  to  weight  (24.82  per  cent)  than  as  to  any  other  character 
measured.  This  is  to  be  expected,  because  weight  is  to  some 
extent  the  resultant  of  both  length  and  circumference  and  would 
thus  partake  of  the  variability  of  both.  But  we  note  also  that 
this  corn  at  least  was  much  more  variable  as  to  length  than  as  to 
circumference  (14.53  Per  cent  as  compared  with  8.06  per  cent). 

Again  we  note  that  these  ears  are  much  more  variable  as  to 
number  of  rows  than  as  to  circumference,  by  which  we  infer 
that  the  width  of  the  kernels  is  far  from  uniform,  else  the  two 
would  move  together. 

This  raises  the  whole  question  of  the  relation  or  bond  between 
different  characters,  a  subject  to  be  discussed  in  the  succeeding 
chapter  on  "  Correlation."  It  is  sufficient  here  to  remark  that 
the  typical  ear  of  this  crop  of  corn  is  8.829  inches  long,  7.047 
inches  in  circumference,  has  20.09  rows  of  kernels,  and  weighs 
12.75  ounces.  If  we  should  pick  such  an  ear  it  could  stand  as 


TYPE  AND   VARIABILITY  445 

the  actual  type  of  this  crop,  though   the  different  characters 
involved  would  vary  differently  from  this  type  or  mean. 

SECTION   VI  —  EFFECT   OF   SELECTION  UPON  TYPE 
AND  VARIABILITY 

The  whole  purpose  of  selection  is  to  influence  type.  In  the 
minds  of  some  it  is  also  to  reduce  variability.  The  real  effect  of 
selection  is  well  brought  out  in  data  (see  table,  page  446)  from 
Dr.  Hopkins's  experiments  1  in  endeavoring  to  influence  chemical 
composition  of  corn  by  the  method  of  selection.  It  is  to  be 
noted  that  all  four  strains  sprung  from  the  same  original  stock 
(163  ears),  and  that  each  seed  selection  was  made  from  the 
highest  (or  lowest)  ears  within  the  several  strains ;  that  is,  the 
high-oil  stock,  for  example,  originated  from  those  ears  show- 
ing the  highest  oil  content  in  the  original  stock,  and  was 
developed  by  successive  selection  of  the  highest  oil  ears,  always 
within  the  high-oil  stock,  and  similarly  for  the  other  strains. 

Discussion  of  data.  A  critical  study  of  the  columns  of  means 
shows  a  steady  rise  in  the  means  of  both  high-protein  and  high- 
oil  strains  and  a  corresponding  decline  in  low-protein  and 
low-oil  strains,  indicating  a  prompt  response  to  selection.  An 
inspection  of  the  columns  of  standard  deviations  and  coefficients 
of  variability,  however,  reveals  the  fact  that  the  variability 
is  practically  unchanged.  This  agrees  with  the  mathematical 
theory,  to  be  developed  later,  namely,  that  the  effect  of  selection 
is  to  shift  the  type  but  not  greatly  to  reduce  variability. 

The  peculiarity  of  this  sort  of  selection  is  that  it  is  progres- 
sive ;  that  is  to  say,  with  each  response  to  selection  a  new 
standard  is  set  up  still  more  difficult  to  meet  than  was  the 
old  one.  Under  these  conditions  of  continuously  advancing 
standards  and  with  rapidly  advancing  types,  in  only  two  out  of 
the  four  cases  was  the  variability  apparently  reduced,  and  this 
whether  we  regard  the  standard  deviation  or  the  coefficient  of 
variability.  This  power  of  response  to  the  demands  of  an  ad- 
vancing standard  of  selection  is  immensely  suggestive  and  will 
be  considered  further  under  "  Heredity." 

1  See  Bulletin  Xo.  119,  University  of  Illinois  Agricultural  Experiment  Station. 


446 


TRANSMISSION 


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TYPE  AND   VARIABILITY 


447 


SECTION  VII  — INDIRECT  EFFECTS  OF  SELECTION  UPON 
TYPE  AND  VARIABILITY 

In  the  table  just  given  we  noted  only  the  direct  effects  upon 
the  character  undergoing  selection.  It  now  remains  to  consider 
how  rigid  selection  of  one  character  may  affect  other  and  pre- 
sumably correlated  characters.  To  this  end  we  construct  a 
table  showing  the  physical  characters  of  the  four  strains  of 
corn  now  under  discussion,  remembering  that  these  strains  all 
developed  from  the  same  original  stock  and  that  selection  was 
confined  to  the  chemical  characters,  protein  and  oil,  leaving  the 
physical  and  physiological  characters  free  to  take  care  of 
themselves. 

INDIRECT  EFFECTS  OF  SELECTION  :  RESULTS  OF  SEVEN  YEARS'  SELEC- 
TION FOR  CHEMICAL  COMPOSITION  UPON  PHYSICAL  CHARACTERS. 
ALL  FOUR  STRAINS  DEVELOPED  FROM  THE  SAME  ORIGINAL  STOCK  l 


VARIETY 

LENGTH  OF  EAR 

CIRCUMFERENCE 

i 

3 

3 

4 

5 

6 

Mean 

Stand.  Dev. 

Coef  .  Var. 

Mean 

Stand.  Dev. 

Coef.  Var. 

A.  High-protein  .  . 
B.  Low-protein    .  . 
C.  High-oil    .... 
D.  Low-oil  

7.21  ±  0.04 
7.80  *  0.04 
6.87  ±  0.04 
7.48*0.04 

1.27  ±0.03 
i.  54  d=  0.03 
i.  39  ±0.03 
1.30*0.03 

17.6  ±0.4 
19.7*0.4 

20.2  ±0.4 
17.4*0.4 

5.76*0.01 

6.51  ±0.02 

6.05  ±  o.oi 

6.65  ±  O.O2 

0.44  *  o.oi 
0.61  ±0.01 
0.53  ±0.01 
0.59  ±  o.oi 

7.6*0.2 
9.4*0.2 
8.8  *  0.2 

8.9  ±  O.2 

VARIETY 

NUMBER  OF  Rows 

WEIGHT  OF  EARS 

7 
Mean 

8 
Stand.  Dev. 

9 
Coef.  Var. 

10 

Mean 

II 
Stand.  Dev. 

13 

Coef.  Var. 

A.  High-protein  .  . 
B.  Low-protein    .  . 
C.  High-oil     .... 
D.  Low-oil  

1  3.  72  ±0.03 
14.17  ±0.06 
15.65  ±0.06 

12.  80  ±0.05 

i  .85  ±  0.02 
i  .94  *  0.04 
2.08*0.04 
1.77*0.04 

13.5*0.2 
13.7  ±0.3 
13.3  ±0.3 
13-8  ±0,3 

7.53  ±  0.04 
9.66  ±0.10 
7.79  ±  0.07 
9.84  ±  0.08 

2.50*0.03 
3.30  ±  0.07 
2.43  ±0.05 
2.87  ±  0.06 

33.2*0.4 
34-2  *  0.7 
31.2  ±0.6 
29.2  ±  0.7 

Discussion  of   data.    A   critical   study  of  this   table   reveals 
some  significant  facts  concerning  the  indirect  effects  of  selection 

1  See  Bulletin  No.  7/9,  University  of  Illinois  Agricultural  Experiment  Station. 


448  TRANSMISSION 

upon  characters  other  than  those  under  special  consideration. 
Such  a  critical  study  develops  the  fact  that  these  four  strains 
differing  in  protein  and  in  oil  content  have  developed  also  into 
four  distinct  strains  regarding  the  purely  physical  characters,  — 
length,  circumference,  etc. 

1.  High  and  loiv  protein.    The    ear    of    the    former  is    the 
shorter  (column  i),  and  the  smaller  standard  deviation  and  co- 
efficient of  variability  show  it  to  be  less  variable  as  to  length 
(columns  2  and    3).    It  is  also  smaller  in  circumference  (col- 
umn 4),  with  a  less  number  of  rows  (column  7),  and  lighter  in 
weight  (column  10).    It  is  also  less  variable  in  every  respect, 
both  relatively  (columns  2,  5,  8,  and   n)  and  absolutely  (col- 
umns 3,  6,  9,  and  12). 

2.  High  and  low  oil.    In  the  same  manner  we  learn  that  the 
high-oil  ear  is  a  shorter  and  a  smaller  ear  than  the  low-oil,  but 
that  it  is  more  variable  as  to  length  and  less  variable  as   to 
circumference  (columns  i  to  6).  The  low-oil  ear  is  rapidly  becom- 
ing a  twelve-rowed  variety,  with  a  lower  deviation  than  any 
other  (column  8).    It  is  the  heaviest,  though  not  the  longest,  of 
the  four  selected  strains. 

3.  The  four  selected  strains.    Of  these  four  strains  developed 
from  the  same  original  stock,  the  low-protein  ear  is  the  longest 
and  the  high-oil  the   shortest.     The   high-oil  is  also  the  most 
variable  as  to  length  (column  3). 

The  low-oil  is  the  largest  and  the  high-protein  is  the  smallest 
in  circumference.  The  latter  is  also  the  least  variable  and  the 
low-protein  is  the  most  variable  as  to  circumference. 

The  high-oil  corn  has  the  largest  number  of  rows,  with  the 
lowest  variability,  and  the  low-oil  the  fewest  rows,  with  the 
least  standard  deviation  but  the  greatest  coefficient  of  variability. 

The  low-oil  is  the  heaviest  and  the  high-protein  the  lightest 
ear,  but  the  low-protein  is  the  most  variable  as  to  weight. 

It  will  be  noted  that  these  differences  are  the  natural  results  of 
selecting,  not  for  these  particular  characters,  but  for  chemical 
content.  They  are  therefore  the  indirect  effects  of  selection, 
and  bring  up  again  the  whole  subject  of  correlation,  which  will 
be  treated  further  in  a  later  chapter. 


TYPE   AND   VARIABILITY 


449 


SECTION  VIII  — STUDIES  IN  TYPE  AND  VARIABILITY 

OF  THE  SAME  VARIETY  OF   CORN  RAISED  UNDER 

DIFFERENT  CONDITIONS  AS  TO  FERTILITY 

The  effect  of  the  conditions  of  life  upon  variability,  as  distinct 
from  mere  development  of  the  mass,  is  well  illustrated  in  the 
behavior  of  a  single  variety  of  corn  (Learning)  grown  under 
different  conditions  as  to  fertility.  This  was  the  crop  of  1906 
upon  land  that  had  been  in  pasture  for  eighteen  years  previous 
to  1895,  in  a  three-year  rotation  of  corn,  oats,  and  clover  from 
that  time  till  the  present,  with  the  fertility  treatment  indicated 
in  the  tables  (pages  450  and  45  i)  since  the  year  1901. 

Discussion  of  data.  As  to  weight  of  ear,  it  will  be  noted  (see 
tables,  pages  450  and  451)  that  the  mode  and  mean  correspond 
very  closely  to  yield ;  that  is,  that  increased  yield  is  mainly  due 
to  heavier  ears.  This  is  inevitable  from  the  uniform  method  of 
planting  with  two  stalks  to  the  hill.  In  respect  to  variability, 
however,  we  can  detect  little  difference  except  in  the  last  plot, 
which  was  planted  with  three  stalks  to  the  hill. 

In  respect  to  length  and  circumference  of  ear  it  is  noticeable 
that  the  higher  yields  are  accompanied  by  the  longer  and  larger 
ears  for  the  reasons  given  above.  The  most  significant  fact  in 
the  table  is  that  corn  is  far  more  variable  as  to  length  than 
as  to  circumference,  but  that  neither  is  especially  affected  by 
fertility.  » 

A  general  correspondence  between  circumference  and  number 
of  rows  is  evident,  showing  a  tendency  to  constancy  as  to  size 
of  kernel,  but  again  variability  is  not  greatly  different  for  the 
different  yields.  So  far  as  this  instance  can  be  accepted  as  a 
safe  criterion,  we  may  deduce  the  following  principles  : 

1.  That  type  is   directly  and  largely  dependent  upon  food 
supply. 

2.  That    variability    is   not    greatly    influenced    by   specially 
favorable  conditions  of  life,  tending  to  become  less  rather  than 
greater  as  all   individuals  are  afforded   ideal  opportunities  for 
development. 


450 


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41       41       41        41        41       41       41       41       41       41 

S-o^n    g^s^^vS'S-a 

vO         •^•ON.iOOOO          roiH         «         O- 

9POK 

OO\OOO\OOOOOOCOOOOvO 

CIRCUMFERENCE  OF  EARS 

*•       >, 

^             ^.      ^      -too 

Coefficiei 
of 
Variabilil 

o      d      d      d      d      o"      d      d      d      d 
41       41       41       41       41       41       41       41       41       41 

NvO          N          OOO          "2          8xr°^N 

•E  § 
II 

•O^lOvQ           ^^CON           ^-00 

qqqooooooo 
o      o      o      d      d      o"      d      d      d      d 

41       41       41       41       41       41       41        41       41       41 

W  fl 

d      d     d      o      d      d     d      d      d      d 

§ 

q       q       o       q       q       q       q       o5      q       o 
o      d      d      d      d      d      d      d      d      d 
4I414I414I4I4I4I4I4I 

?  5   ?l^5SaSi 

3poW 

vd       xO        vd       vd       >0        vd       vd       >d       VC        vd 

Coefficient 
of 
Variability 

d      d      d      d      d      d      d      d      d      d 
41       41       41       41       41       41       41       41       41       41 
q>«       1000*100?       JON       oo^ 

NNNNMHiir^'wN 

in 

K 

W 
h 

0 

Standard 
Deviation 

d      d      d      d      d      d      d      d      d      d 
4I4I4I4I414I4I4I4I4I 

H 

i 

o(?o      0*0^0      o      H      9*     ? 
d      d      d      d      d      d      d      d      d      d 

M.vi  i  ?  ii  f  i 

txtxtxr«.t^oooo       t^oo       t^ 

3porc 

t^oooo       t^oooo       o«ooodoo* 

M3JIK.1JVJ    X01J 

o       o       goo1!       crl)       8^2 

452  TRANSMISSION 

SPECIAL  EXERCISES 

The  student  should  have  extensive  practice  in  making  frequency  distri- 
butions of  different  species  and  in  working  out  standard  deviations  and 
coefficients  of  variability.  He  will  thus  not  only  become  familiar  with  the 
methods  of  work,  but  he  will  acquire  new  conceptions  of  the  whole  subject 
of  variability  and  type.  The  teacher  should  require  the  student  at  this 
point  to  make  original  studies  on  his  own  account,  and  to  prosecute  the 
work  until  he  becomes  entirely  familiar  both  with  the  methods  and  with  the 
conceptions  involved. 


ADDITIONAL  REFERENCES 

THE  GRAMMAR  OF  SCIENCE.    By  Karl  Pearson.    Chapter  X. 
VARIATION  IN  ANIMALS  AND  PLANTS.    By  H.  M.  Vernon.    Chapter  I. 


CHAPTER  XIII 

CORRELATION 

When  studying  variability  in  its  simplest  form  we  take  the 
characters  separately  and  determine  how  each  behaves  with 
reference  to  itself  alone ;  that  is,  with  reference  to  its  own 
range  and  type. 

SECTION   I  — MEANING  OF  CORRELATION 

As  the  study  proceeds,  however,  and  is  extended  to  other 
particulars,  it  will  be  noted  that  certain  characters  tend  to  rise 
and  fall  together,  as  if  connected  by  some  causative  relation,  — 
for  example,  length  and  weight  of  ears,  or  size  and  strength  of 
horses ;  while  others  appear  to  vary  quite  independently  of  one 
another,  as  stature  and  intellectual  power  in  man,  or  color  and 
feeding  quality  in  animals. 

The  whole  subject  of  correlation  refers  to  that  interrelation 
between  separate  characters  by  which  they  tend,  in  some  degree 
at  least,  to  move  together.  This  relation  is  expressed  in  the 
form  of  a  ratio.  Thus,  if  an  increase  of  one  character  is  always 
followed  by  a  corresponding  and  proportional  increase  in  a  re- 
lated character,  the  correlation  is  said  to  be  perfect  and  the 
ratio  is  I.  On  the  other  hand,  if  an  increase  in  one  character 
is  followed  by  a  corresponding  and  proportional  decrease  in  a 
related  character,  the  correlation  is  said  to  be  negative  and  the 
ratio  is  —  i,  or  perfect  negative  correlation.  Still  again,  if  the 
characters  in  question  are  absolutely  indifferent  the  one  to 
the  other,  the  correlation  is  said  to  be  zero,  indicating  mere 
association  under  the  law  of  independent  probability,  without 
causative  relation  of  any  kind. 

Examples  of  perfect  correlation  are  furnished  by  such  obvious 
relations  as  those  between  the  power  of  sight  and  the  presence 
of  eyes  ;  the  giving  of  milk  and  the  presence  of  an  udder  ;  the 

45.3 


454  TRANSMISSION 

presence  of  sunlight  and  the  fixing  of  carbon ;  and  by  such 
other  relations  as  are  involved  in  direct  causation. 

On  the  other  hand,  such  a  relation  as  deafness  among  teleg- 
raphers or  blindness  among  civil  engineers  or  locomotive  drivers 
is  unknown,  because  the  conditions  are  such  that  the  characters 
in  question  are  mutually  exclusive. 

In  general,  however,  correlation  falls  somewhere  between  —  i 
and  unity,  and  on  one  side  or  the  other  of  the  zero  point ;  that  is, 
a  degree  of  relationship  exists  which  is  neither  absolute,  denot- 
ing direct  causation,  nor  negative,  signifying  mutual  exclusion. 
For  example,  a  high  degree  of  correlation  exists  between  length 
of  cob  and  weight  of  ear.  It  does  not  amount  to  unity,  however, 
for  the  circumference  also  contributes  to  weight. 

Most  results  in  living  organisms  are  the  effect  of  mixed 
causes,  and  for  this  reason  correlations  are  more  complicated 
than  may  at  first  appear.  For  example,  many,  if  not  most,  good 
cows  have  a  capacious  "  barrel"  and  a  roomy  udder,  and  men 
have  been  led  to  assume  a  perfect  correlation  between  these 
special  characters  and  milk  production;  whereas  the  truth  is 
that  the  correlation,  though  high,  is  something  less  than  unity, 
because  good  cows  are  known  with  small  barrels  and  with  incon- 
spicuous udders.  Here  is  a  real  need  for  accurate  methods  of 
determining  what  degree  of  correlation  actually  exists.  The 
average  man  asks  whether  or  not  two  characters  are  correlated, 
and  expects  a  positive  answer  Yes  or  No ;  whereas  the  question 
should  be,  To  what  extent  do  the  two  characters  appear  together? 
expecting  for  an  answer  a  fraction  lying  somewhere  between 
zero  and  unity,  say  perhaps  40  to  60  per  cent,  as  in  correlation 
of  length  to  weight  of  ear. 

The  student  must  distinguish  clearly  between  correlation  and 
mere  association.  For  example,  we  might  ask  the  question  whether 
black  pigs  are  more  subject  to  cholera  than  are  pigs  of  other 
colors.  The  first  step  would  be  to  establish  a  ratio  between  the 
number  of  diseased  pigs  and  pigs  in  general.  This  ratio  would 
now  express  the  chances  that  a  particular  pig,  irrespective  of 
color,  will  be  afflicted  with  this  disease,  —  that  is,  by  that  opera- 
tion of  independent  probability  which  we  call  chance.  If  now 
we  find  upon  inquiry  that  under  the  same  conditions  the  ratio 


CORRELATION 


455 


of  cholera  subjects  to  black  pigs  is  higher  than  the  ratio  to  pigs 
in  general,  then  we  should  conclude  that  an  actual  positive  corre- 
lation exists  between  the  black  color  and  this  particular  disease. 
On  the  other  hand,  if  this  ratio  should  be  below  the  ratio  of 
pigs  in  general,  then  we  should  conclude  that  black  pigs  are 
less  susceptible  to  this  disease  than  are  pigs  of  other  colors,  and 
that  a  negative  correlation  exists,  assuming  always  equal  oppor- 
tunities for  infection.  This  is  the  only  correct  method  of  study, 
and  it  would  not  be  safe  to  conclude  that  black  pigs  are  pecul- 
iarly susceptible  simply  because  most  of  the  pigs  that  died  under 
our  observation  happened  to  be  black,  for  black  pigs  are  more 
numerous  in  the  cholera  belt  than  all  others  combined,  and 
under  probability  alone  their  absolute  mortality  must  be  higher. 
When  expressed  in  the  form  of  a  ratio,  however,  the  truth  comes 
to  the  surface.1 

Similarly  we  may  ask  the  question  whether  different  species 
of  plants  or  animals  tend  to  attract  or  repel  each  other  when 
thrown  together  in  the  same  territory.  Here  again  the  first 
step  is  to  find  the  ratio  of  association  under  free  operation  of 
independent  probability,  —  a  ratio  based  on  the  relative  numbers 
of  individuals  of  the  species  in  question  and  the  extent  of  terri- 
tory, first  where  no  opportunity  for  association  is  possible,  and 
second,  where  such  association  is  possible.  If  the  two  ratios 
differ,  then  we  infer  that  some  degree  of  correlation  exists. 

SECTION   II  —  CALCULATION   OF  COEFFICIENTS  OF 
CORRELATION 

When  the  presence  or  absence  of  the  characters  in  question 
is  absolute,  as  red  or  black  hair,  presence  or  absence  of  horns, 
then  the  correlation  is  expressed  by  a  single  ratio,  as  we  have 
seen.  But  most  cases  are  not  of  this  extreme  simplicity ;  for 
example,  it  is  said  that  white  cats  are  deaf.  If  now  all  white 
cats  are  deaf,  then  the  correlation  between  albinism  and  loss  of 
hearing  power  is  absolute,  and  is  expressed  by  the  coefficient  i. 

1  Perhaps  it  ought  to  be  remarked  that  this  illustration  is  taken  purely  at 
random,  as  no  studies  have  been  made  as  to  the  relation  between  color  and  this 
particular  disease. 


456 


TRANSMISSION 


Suppose,  however,  that  out  of  1000  cats  taken  at  random 
20  are  white,  10  are  deaf,  and  6  are  both  white  and  deaf. 
Is  there  correlation  ?  Now,  according  to  this  assumption,  the 
probability  of  a  cat  being  deaf  without  respect  to  color  is 
10-^-1000,  or  i  to  100;  but  the  probability  of  a  white  cat 
being  also  deaf  amounts  to  6  -j-  20,  or  -fa,  showing  a  high  corre- 
lation between  albinism  and  deafness. 

But  to  derive  an  exact  expression  for  this  correlation  is  not 
so  simple  as  it  might  seem.  According  to  the  conditions  which 
we  have  already  laid  down,  and  in  consistency  with  other  phases 
of  the  problem  of  correlation  in  general,  any  expression  which 
we  may  adopt  as  an  efficient  measure  of  this  correlation  should 
be  such  a  formula  as  will  become  zero  when  the  two  characters 
are  indifferent  to  each  other  ;  will  become  i  when  the  two  move 
together  perfectly  ;  and  will  become  —  i  when  they  are  mutually 
exclusive. 

Yule1  has  given  an  elegant  measure  of  this  association,  or 
correlation,  which  satisfies  these 
conditions.  To  develop  this  for- 
mula he  arranges  the  population 
as  in  the  accompanying  diagram 
with  respect  to  the  characters 
in  question  (deafness  and  color). 

Then  the  measure  of  associ- 
ation between  deafness  and  the  white  color  is  expressed  by 

(6  x  976) -(4  X  14)  = 

(6  x  976) +  (4  X  14) 
In  general,  if  we  have  a  popu- 
lation arranged  with  reference  to 
the  presence  or  absence  of  two 
characters,  M  and  N,  in  num- 
bers a,  b,  c,  d>  the  arrangement 
would  stand  the  same  as  above, 

and  the  formula  would  be 


CATS 

WHITE 

NOT  WHITE 

Deaf 

6 

4 

Not  deaf 

14 

976 

M  PRESENT 

M  ABSENT 

N  PRESENT 

a 

* 

N  ABSENT 


If  care  be  taken  to  arrange 
ad  +  be 

the  table  so  that  be  shall  be  numerically  less  than  ad,  then  the 


Philosophical  Transactions  of  the  Royal  Society,  CXIV,  257-319. 


CORRELATION 


457 


correlation    is    positive.     Whenever  ad  and   be  become    equal 

the  formula  becomes  -          -  =  o,  or  no  correlation  ;  whenever 
ad  +  be 

b  or  c  becomes    zero,    then    the   formula    becomes   --  =  i    or 

ad 

perfect    positive    correlation ;   and   whenever  a  or  d  becomes 

zero,  then  the  formula  becomes  =  —  i ,  or  perfect  negative 

correlation. 

This  is  the  simplest  formula  proposed  that  will  meet  the 
necessary  conditions  of  the  case.  Pearson  l  has  proposed  several 
others  that  are  much  more  complicated,  and  that  differ  slightly 
as  to  results.  Strange  as  it  may  seem,  the  problem  is  a  com- 
paratively new  one,  though  the  question  involved  is  fundamental 
and  very  old.  Though  other  methods  are  in  use  for  special 
cases  we  may  safely  use  Yule's  formula  for  all  ordinary  cases 
of  association  where  the  question  is  simply  as  to  presence  or 
absence,  without  involving  considerations  of  degree ;  that  is  to 
say,  when  the  question  is  whether  or  not  the  cats  are  deaf, 
without  reference  to  degrees  of  deafness  ;  whether  or  not  the 
patient  has  smallpox,  without  reference  to  the  severity  of  the 
attack. 

When,  however,  the  question  is  one  of  possible  correlation 
between  characters  present  in  varying  degrees,  as  size,  weight, 
amount  of  milk,  etc.,  the  problem  would  seem  at  first  thought 
to  be  far  more  difficult ;  but  in  truth  it  has  been  much  more  com- 
pletely worked  out  than  the  preceding  question. 

For  example,  what  is  the  correlation  between  length  and  cir- 
cumference in  ears  of  corn  ?  In  general,  long  ears  are  also  large 
ears,  but  many  can  be  found  that  are  long  and  slender,  many 
that  are  short  and  small,  and  still  others  that  are  short  and  large. 
In  other  words,  the  two  characters,  length  and  circumference, 
are  so  related  that  the  two  maxima  may  appear  together,  the 
two  minima  together,  the  maximum  length  and  the  minimum 
circumference  and  vice  versa,  and  all  grades  between.  What 
now  is  the  correlation  ?  To  answer  a  question  thus  complicated 
we  construct  what  is  called  a  correlation  table. 

1  Philosophical  Transactions  of  the  Royal  Society,  CXCV,  1-47. 


458  TRANSMISSION 

.SECTION   III— THE   CORRELATION  TABLE 

To  determine  the  degree  of  correlation  between  any  two 
characters  in  any  race,  a  so-called  "  correlation  table  "  is  con- 
structed out  of  the  measurements  of  the  two  characters  as  found 
in  a  large  number  of  individuals,  one  character  being  recorded 
in  columns  and  the  other  in  rows.  Two  records  are  thus  made 
of  the  same  individual,  one  for  each  character.  Such  a  table, 
when  finished,  consists  of  a  double  system  of  arrays,  each 
dependent  on  the  other,  and  from  whose  means  and  standard 
deviations  the  mutual  relationships  can  readily  be  worked  out. 

Knowing  this  relationship  and  the  value  of  one  of  the  char- 
acters we  are  enabled  to  calculate  the  corresponding  mean  value 
of  the  other.  The  advantages  of  this  for  purposes  of  selection  are 
obvious.  The  method  is  best  illustrated  by  an  actual  example. 

For  instance,  it  is  evident  that  the  weight  of  ears  in  corn  de 
pends  partly  upon  their  length  and  partly  upon  their  circumfer- 
ence. To  what  extent,  for  example,  does  it  depend  upon  length  ? 

In  order  to  answer  this  question  definitely  a  large  number  of 
ears  taken  at  random  are  both  weighed  and  measured,  and  the 
data  are  arranged  in  tabular  form  as  described  above,  appearing 
as  follows  : 

CORRELATION  BETWEEN  WEIGHT  AND  LENGTH  OF  EAR 
(LEAMING  CORN) 

WEIGHT  OF  EARS  IN  OUNCES 


7. 

•        3        4 

2 

5 

6 

7 

8 

9 

IO 

11         12         13 

M 

IS 

16     17      18      ig     20     21 

4 

T 

4. 

I        C         C 

T 

4-5 
c. 

6     5 

2       4 

4 
7 

I 

• 



c.c 

2       Q 

I  c 

14. 

A 

I 

6 

I        2 

12 

1  6 

M 

J  1 

6 

j 

6.5 

7- 

I 

6 

2 

1  1 

2 

2 

12 
4 

II 

18 

20 

7 

8 

12 
12 
IQ 

6 

12 

I 

ii      4      i 

21     II        6 

17     ''''     17 

6 

* 

I 

I       

8.5 

j 

I 

1  2 

-5 

23  30  ->6 

"6 

j 

q. 

I 

7 

IO     '''J     1$ 

•>  4 

I  "*      I       ^        I 

Q.C 

1W    *J    J.) 
41  J.     I  Q 

°Q 

j  7 

10    i      3            ii 

IO. 

I 

i      i     8 

iS 

IO 

6    a      -» 

fj 

I  I. 

I 

I 

7251 

2         I 

II.  S 

I 

CORRELATION  459 

Arrays  of  a  correlation  table.  In  this  table  each  ear  is 
recorded  in  the  proper  square  to  represent  both  its  weight  and 
its  length.  This  being  the  case,  all  the  ears  of  the  same  weight 
that  are  also  of  the  same  length  are  recorded  together  in  the 
same  square.  This  means  that  the  various  rows  are  frequency 
distributions  of  weight  with  respect  to  length  (as  i,  6,  n,  26, 
11,  8,  6,  i,  the  frequency  distribution  corresponding  to  the 
length  6.5  inches),  and  all  the  columns  are  frequency  distributions 
of  length  with  respect  to  weight.  Such  frequency  distributions 
with  respect  to  a  correlated  character  are  technically  known  as 
"arrays."  The  entire  table,  therefore,  may  be  looked  upon  as 
made  up  of  two  systems  of  parallel  arrays  with  respect  to  the 
two  characters  in  question.  They  are  in  no  respect  different  from 
any  other  frequency  distributions ;  and  their  means,  standard 
deviations,  variability,  and  other  determinations  are  calculated 
by  the  same  methods  as  given  in  the  last  chapter. 

SECTION   IV  — THE   CORRELATION   COEFFICIENT 

A  mere  inspection  of  the  correlation  table  just  given  suggests 
that,  in  general,  short  ears  are  light  ears,  and  that  long  ears  are 
heavy  ears  ;  but  what  we  seek  is  a  statistical  constant  which 
will  be  a  measure  of  this  correlation,  and  which  indicates  to 
what  extent  the  weight  of  ears  can  be  predicted  from  their 
lengths.  The  coefficient  of  correlation  is  such  a  constant,  and 
when  determined  it  will  be  denoted  by  r. 

A  discussion  of  the  mathematical  theory  of  correlation  will 
be  given  in  the  Appendix,  but  it  should  be  said  here,  as  before, 
that  the  coefficient  always  takes  some  value  between  +  i  and 
-i.  If  r==+  i,  there  is  said  to  be  perfect  positive  correla- 
tion; that  is,  the  two  characters  are  causally  connected.  If 
r  —  —  i  there  is  perfect  negative  correlation;  that  is,  they 
are  mutually  exclusive.  If  no  correlation  exists,  r  =  o^.  indicat- 
ing the  two  characters  as  being  indifferent  to  each  other  and 
moving  independently.  In  nearly  all  cases  some  actual  correla- 
tion exists,  and,  in  a  general  way,  we  may  say  that  the  correla- 
tion should  be  judged  by  the  value  which  r  takes  between  zero 
and  unity. 


460  TRANSMISSION 

Method  of  finding  correlation  coefficient.  The  method  of  cal- 
culating the  correlation  coefficient  (r)  is  exhibited  in  connection 
with  the  table  on  page  461,  showing  a  representative  case,  for 
convenience  continuing  the  same  correlation  table  already  con- 
structed. Though  the  method  is  somewhat  complicated  it  is 
given  in  full. 

It  is  highly  important  to  get  at  once  a  general  conception  of 
this  table  and  of  the  method  of  procedure.  All  the  computa- 
tions shown  except  those  involved  in  the  column  headed  2P 
have  to  do  only  with  finding  the  means  and  standard  deviations 
of  the  population  with  respect  to  the  two  characters  in  question, 
according  to  the  method  fully  treated  in  the  last  chapter ;  that 
is  to  say,  the  columns  of  figures  headed  *  fL,  fL  VL,  DL,  DL2, 
fif>L>  f-m  firVir*  DM  D>*>  fu'Di?  are  all  self-explanatory  to 
any  one  familiar  with  the  meaning  of  ordinary  algebraic  symbols, 
and  who  knows  how  to  find  the  variability  of  a  population  by  the 
methods  already  given. 

There  remains  the  column  of  figures  headed  2P,  which  it 
seems  worth  while  to  explain  in  detail  and  which  is  the  only 
special  feature  in  the  determination  of  the  correlation  coefficient. 
Each  number  in  this  column  represents  the  sum  of  the  products 
of  the  corresponding  length  and  weight  deviations  for  every 
individual  in  the  horizontal  array  to  which  the  number  belongs. 

To  show  how  these  numbers  are  computed,  select,  for  example, 
the  horizontal  array  marked  10,  and  we  shall  show  how  to  find 
the  number  431.0. 

In  this  case 

10  —  7.8,  the  mean,  =  2.2  =  DL  of  row  10. 
Then 

2.2  [i  (-  0.7)  +  i  (0.3)  +  3  (1.3)  +  8  (2.3)  +  18  (3.3) 

+  10  (4.3)  +  6  (5.3)  +  4  (6.3)  +  2  (7.3)]  =  431-0. 

All  other  numbers  of  the  column  headed  2P  are  found  in  the 
same  way,  and  the  total  is  written  symbolically  as  *2DLDn,? 

1  Read  "/"sub  /r,"  meaning  the  frequency  of  weights ;  "/sub  w  Fsub  /^"mean- 
ing the  frequency  of  weights  multiplied  by  the  value  in  weights  ;  "/sub  /,,"  mean- 
ing the  frequency  of  length,  etc. 

'2  The  real  significance  of  !LP  is  best  shown  by  the  expression  SZ? /./?// ,  that 
is,  the  sum  of  the  products  of  both  deviations  of  all  the  individuals  in  the  table. 
It  is  written  in  various  ways,  but  always  with  the  above  meaning. 


CORRELATION 


461 


CORRELATION  OF  WEIGHT  OF  EARS  RELATIVE  TO  LENGTH  OF  EARS 
(LEAMING  CORN)  1 


WEIGHT  OF  EARS  IN  OUNCES 

O      U 


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NOTATION  : 


2432.9  4947.2 

M^—  7.85-  ±0.03 
•  • 
<rL=2-45 

<TL  =  i.  57  ±0.02 


*•! 


£  993(i.57)(3-°3) 

o         ^=^45(_i-^ooo. 

II  V« 

^   ^    correlation  coefficient 

^         O.  =  O.  87  dr.  0.005 

•H     7 — ^.'=^6.03  ± '0.02 

^    t^  =  regression  of  weight 

II     ||  relative  to  length 

q*Noqi/)N.vqq>>oqi-i     M  "&  £  r — :_  0.38  ±0.005 

=  regression  of  leng'.h 

relative  to  weight 
/L=  class  frequencies  of  total  population  with  respect  to  length. 
^  L  =  value  or  measurement  corresponding  to  a  given  frequency  with  respect  to  length 
M^=  mean  length  of  ears. 

.£>L=  deviation  of  ear  lengths  from  mean  length. 
0*L=  standard  deviation  of  length  of  ears. 

fw=  class  frequencies  of  total  population  with  respect  to  weight. 
•  rqf*f  value  corresponding  to  a  given  frequency  with  respect  to  weight. 
-^/w=  mean  weight  of  ears. 
•D\iv=  deviation  of  weight  from  mean  weight. 
<TL=  standard  deviation  of  weight  of  ears. 
r=  coefficient  of  correlation. 

r     u      coefficient  of  regression  of  weight  witli  respect  to  length. 


We  have  retained  ;i  minimum  of  decimal  places  in  this  table  in  order  to  save  space. 


462  TRANSMISSION 

The  value  of  r  is  found  by  means  of  the  formula 


Systematic  arrangement  of  work.  The  whole  process,  which 
seems  somewhat  complicated,  is  after  all  quite  simple.  To 
recapitulate,  it  amounts  to  multiplying  the  figures  in  each  square 
by  both  their  own  deviations  (that  is,  by  their  deviation  as  to 
length  and  their  deviation  as  to  weight),  and  then  adding  all  the 
results  and  dividing  by  the  whole  number  (of  ears)  multiplied 
by  the  product  of  the  two  standard  deviations.  (See  formula 

r  =  ~^~^JK')   In  performing  the  actual   work,  however,   it  is 

highly  important  to  have  a  systematic  scheme  for  carrying  out 
the  computations  in  order  to  avoid  confusion  in  the  somewhat 
complicated  details.  It  has  seemed  desirable,  therefore,  to 
present  the  matter  in  the  form  of  a  detailed  description  of  the 
various  steps  involved. 

•First  step.  Having  given  the  correlation  table  of  the  popula- 
tion, we  first  add  the  frequencies  in  the  arrays  with  respect  to 
both  characters  ;  that  is,  add  the  numbers  in  columns  and  rows 
of  the  table.  This  gives  two  frequency  distributions  of  the  total 
population,  —  the  one  with  respect  to  length  of  ears  (/,),  and  the 
other  with  respect  to  weight  of  ears  (/^). 

The  one  with  respect  to  length  has  the  frequencies  4,  5,  14, 
16,  19,  53,  64,  70,  75,  98,  114,  134,  142,  100,  53,  26,  5,  i. 

The  one  with  respect  to  weight  has  the  frequencies  4,  22,  27, 
50,  47,  71,  75,  71,  75,  88,  107,  114,  112,  65,  37,  8,  13,  4,  2,  i. 

Second  step.  For  each  of  these  frequency  distributions 
(column  fL  and  row  /„,)  the  means  and  the  standard  deviations 
must  be  calculated.  The  method  of  making  these  calculations 
is  the  same  as  the  one  used  for  mean  and  standard  deviations 
in  general.  It  has  already  been  fully  explained,  and  therefore 
need  not  be  repeated  here.  A  systematic  arrangement  of  the 
work  is  shown  in  connection  with  the  table.  The  results  are  : 

mean  length  =  M,  =  7.85 
standard  deviation  in  length  =  o-7  —  1.57 

mean  weight  =  Mlt-  =  10.65 
standard  deviation  in  weight  =  a-,,.  =  3.63,          f' 


CORRELATION  463 

Third  step.  This  is  the  only  part  of  the  work  that  is  really 
new.  In  doing  the  second  step  we  found  the  deviations  of 
the  classes  from  the  mean  length  and  mean  weight.  These  are 
recorded  under  DL  and  Diy.  For  example,  in  row  i  we  find 
that  4  ears  were  each  3  inches  long ;  that  is  to  say,  they 
deviated  — 4.8  inches  from  the  mean  length  taken  at  7.8  in- 
stead of  7.85  in  order  to  save  labor.  We  next  take  the  num- 
ber in  each  square  of  the  correlation  table  and  multiply  it  by 
the  corresponding  deviations  both  in  weight  and  in  length, 
thereby  securing  a  product  which  is  the  result  of  the  full  num- 
ber of  variates  involved  and  of  their  deviation  in  respect  to 
both  characters. 

For  example,  where  the  column  headed  9  ounces  and  the 
row  labeled  6.5  inches  cross  each  other  occurs  the  number 
8,  which  indicates  that  8  ears  of  the  population  weighed  9 
ounces  and  were  6.5  inches  long.  In  other  words,  these  8 
ears  each  deviate  —  1.7  ounces  (row  D^,  column  9)  from  mean 
weight  of  ears,  and  —  1.3  inches  from  the  mean  length  (column 
Z>7,  row  6.5).  Hence  for  this  number  8  we  form  the  product 
8(—  i-7)(—  1.3)  =  +  17.68.  Without  regard  to  labor,  we  should 
find  such  a  product  for  each  number  in  the  correlation  table. 
If  now  all  these  products  be  added  and  the  result  divided  by 
the  product  of  the  two  standard  deviations  into  the  number  of 
variates  in  the  total  population,  we  shall  obtain  the  correlation 
coefficient,  or  the  index  of  correlation  which  we  seek. 

The  systematic  way  of  carrying  out  this  work  is  to  record  the 
results  of  this  operation  for  each  horizontal  array  under  the 
heading  2P,  and  then  add  these  results  for  the  arrays  to  obtain 
the  final  result  4947.2,  which  is  symbolically  indicated  by 
^DLD^  or  summation  DLD^. 

To  illustrate  the  method  of  calculation  a  few  of  the  products 
recorded  in  column  ^P  will  be  shown. 

For  example,  with  7.8  as  the  mean  length  and  10.7  as  the 
mean  weight,  we  have  for  the  array  corresponding  to  length 

4  inches, 

-8.7  x  3 


-  7.7  x  5 
—  3.8  x  —  6.7  x  5 

-  5-7  x  i 


This  gives  394.4. 


464  TRANSMISSION 

For  the  array  corresponding  to.  5  inches, 


-  7.7   X   2 

-6.7  x  4 


This  gives  297.6. 


-  2.8  x  -  5.7  x  7 
-4.7  x  2 
-3-7  x  4 

Treat  all  arrays  in  a  similar  manner,  and,  finally,  divide  the 
sum  of  all  the  products  thus  obtained  (that  is  4947.2)  by  the 
product  of  the  two  standard  •  deviations  and  the  number  of 
variates,  being  careful  always  to  preserve  the  full  distinction  as 
to  plus  and  minus  signs.  This  gives 

r  =  — ^—       —  =  0.87,  the  correlation  coefficient. 

993  (i-5 7)  (3-63) 

The  mathematical  derivation  of  this  coefficient  as  a  measure 
of  correlation  involves  too  much  mathematics  to  be  given  here. 
It  may  be  noticed  from  the  common-sense  standpoint,  however, 
that  it  seems  to  be  a  good  measure  of  correlation.  To  appre- 
ciate the  meaning  of  this  coefficient,  it  should  be  recalled  that 
we  take  the  products  of  both  deviations  for  every  individual  in 
the  table,  add  these  products,  and  divide  the  result  by  the 
number  of  individuals.  This  gives  the  average  of  all  the 
products  of  both  deviations.  We  then  divide  this  average 
product  of  the  individual  deviations  by  the  product  of  the  two 
standard  deviations,  thus  securing  an  expression  whose  value  is 
influenced  by  the  deviation  of  both  characters  with  reference 
each  to  the  other. 

It  requires  but  little  mathematical  insight  to  see  that  if  the 
correlation  is  positive  and  considerable,  positive  values  of  the 
two  characters  correspond  and  negative  values  correspond  ;  and 
further,  that  all  the  products  of  deviations  are  positive.  This 
makes  for  a  large  correlation  coefficient.  On  the  other  hand,  if 
no  correlation  exists,  for  any  value  of  one  character  we  may 
expect  in  the  long  run  equal  and  opposite  deviations  of  the 
other  character,  which  makes  the  sum  of  products  of  deviations 
very  small.  This  common-sense  examination  indicates  the  real 
nature  of  the  correlation  coefficient. 

Fourth  step.  Find  the  probable  errors  in  the  determined  values. 
Those  in  the  means  and  standard  deviations  are  computed  by 


CORRELATION  465 

formulas  stated  in  the  last  chapter.    For  the  probable  error  in 
the  correlation  coefficient  use  the  formula 


V;/ 

Use  of  correlation  coefficient.  The  correlation  coefficient  is  a 
good  index  of  the  mutual  relation  that  exists  between  the  char- 
acters in  question.  If  it  is  low,  it  indicates  that  they  do  not 
depend  very  much  upon  each  other;  if  it  is  high,  it  indicates 
that  they  are  in  some  'way  closely  related ;  and  if  it  rises  to 
unity,  this  relation  amounts  to  causation,  —  that  is,  one  is  the 
cause  of  the  other,  or  else  they  are  the  joint  effect  of  the  same 
causes.  The  practical  advantage  of  this  knowledge  for  purposes  of 
selection  is  obvious,  especially  when  one  character  is  easily  seen 
and  readily  examined  and  the  other  is  not.  An  application  of  the 
correlation  table  would  correct  many  popular  delusions  on  this 
subject,  as,  for  example,  the  selection  of  cows  by  the  escutcheon. 

Shorter  method  for  calculating  r,  the  coefficient  of  correlation. 
There  is  derived  in  the  Appendix  a  formula  which  gives 

the  same  numerical  value  for  r  as — -  already  used ;  and 

n  <TL<TW 

while  its  algebraic  expression  is  a  little  more  complicated,  it  is 
much  better  adapted  to  numerical  calculation,  as  it  avoids  the 
use  of  decimals  until  almost  the  end  of  the  work.  In  this  respect 
it  is  similar  to  the  shorter  method  presented  for  calculating  the 
standard  deviation.  If  applied  to  the  case  of  the  length  and 
weight  of  ears  of  corn  the  formula  is 


/V     r  r  \_L_ 

n  C/-    ">,*,, 


where  £)/,  Dnl  are  deviations  from  our  guess  at  the  means  instead 
of  deviations  from  the  mean  itself  as  DL  and  Dw\  and  CL  and  C,r 
are  the  corrections  applied  to  the  guesses  at  the  mean  length 
and  weight  respectively  as  used  in  the  shorter  method  of  finding 
standard  deviation. 

In  other  words,  we  find  the  standard  deviation  by  the  shorter 
method  explained  on  page  429.  Then,  in  forming  the  sum  of 
products  of  deviations,  we  measure  the  deviations  from  the 
guess  instead  of  measuring  them  from  the  means,  and  divide  as 


466  TRANSMISSION 

before  by  the  product  of  the  number  of  variates  and  the  two 
standard  deviations.  Finally  we  subtract  from  this  result  the 
products  of  the  two  corrections  to  our  guesses  in  finding  means, 
after  dividing  that  product  by  the  product  of  the  standard  devi- 
ations of  the  two  systems  of  variates. 

We  shall  present  on  page  467  an  illustration  of  this  shorter 
method,  using  for  the  purpose  the  correlation  between  length 
and  circumference  of  ears  of  Learning  corn.  In  this  GL  and  Gc 
are  the  guesses  at  the  class  mark  nearest  to  the  mean  of  the 
population  as  to  length  and  circumference  respectively. 

Let  ML  and  Mc  be  the  mean  length  and  circumference  respec- 
tively, and  CL  and  Cc  the  corrections  to  GL  and  Gc  which  give 
ML  and  J/0  so  that  ML  =  GL  +  CL  and  Mc=  Gc+  Cc. 

Also  let  DL  and  Dc'  represent  deviations  of  class  marks 
from  the  guesses  GL  and  Gc  respectively. 

Unless  one  carries  through  a  large  number  of  decimal  places 
the  method  previously  discussed  is  not  only  very  laborious  but 
it  is  much  less  accurate  than  the  shorter  method  here  described. 


SECTION  V  — THE   REGRESSION   COEFFICIENT 

From  the  correlation  coefficient  and  the  standard  deviations 
with  respect  to  two  characters  it  is  easy  to  obtain  what  is  known 
as  the  regression  coefficient.  To  obtain  the  regression  coefficient 
of  the  weight  of  ears  relative  to  their  lengths,  multiply  the 
coefficient  of  correlation  by  the  standard  deviation  of  weight, 
and  divide  the  product  by  the  standard  deviation  of  length. 

This  gives,  for  the  regression  of  weight  relative  to  length, 

°v 
r  —  =  2.03. 

*L 

Similarly,  the  regression  of  length  relative  to  weight  is 

r*>- 

°v 

Use  of  the  regression  coefficient.  The  regression  coefficient  is 
useful  for  prediction ;  that  is  to  say,  if  we  know  the  deviation 
of  one  character  from  its  mean,  this  coefficient  will  enable  us  to 


CORRELATION 


467 


CORRELATION  STUDY  (LEAMING  CORN  CROP,  1905) 


CIRCUMFERENCE.     £0=6.3 


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468  TRANSMISSION 

predict  what  will  probably  be  the  deviation  of  the  correlated  char- 
acter from  its  mean.  Thus,  suppose  we  select  ears  which  deviate, 
say  two  inches,  from  the  mean  length  of  ears  ;  that  is,  which  are 
two  inches  above  the  average  :  the  regression  coefficient  (2.03) 
of  weight  relative  to  length  indicates  that  we  should  expect  such 
ears  to  be  about  4.06  ounces  from  the  mean,  that  is  2  X  2.03. 
To  be  more  general,  if  we  select  ears  which  have  any  deviation 
x  from  the  mean  length,  we  should  expect  their  deviations  in 
weight  to  center  about  a  value  2.03  x  from  the  mean  weight  of 
ears  for  the  whole  population. 

The  regression  coefficient  is  thus  a  fixed  ratio  between  devia- 
tions of  correlated  characters,  so  that,  knowing  how  much  one  of 
the  characters  differs  from  its  mean  in  any  unit  of  measurement, 
say  inches,  we  are  enabled  to  predict  how  much  the  associated 
character  departs  from  its  mean  in  its  unit  of  measurement,  say 
in  pounds.  Thus  if  a  regression  coefficient  of  weight  upon  stat- 
ure is,  say  2.17,  we  know  that  any  departure  from  the  mean 
stature  will  be  followed  by  a  departure  2.17  times  as  great  in 
respect  to  weight,  using  in  both  cases  the  same  units  as  were 
used  in  calculating  the  coefficient ;  for  example,  feet  and  pounds, 
inches  and  ounces,  or  even  inches  and  pounds,  if  these  were  the 
units  actually  used  in  computing  the  regression  coefficient. 

SECTION  VI  — STUDIES  IN  SPEED  RECORDS  OF 
TROTTERS 

Studies  were  made  of  13,879  trotters  possessing  records  of 
2  :  30  or  better,  in  order  to  learn  their  distribution  as  to  speed, 
and  the  possible  correlation  of  speed  with  color,  and  more  par- 
ticularly with  sex  (see  tables,  pages  469  and  470). 

The  data  were  taken  for  each  quarter  second,  and  the  record 
made  a  scroll  over  forty  feet  long.  The  matter  is  here  con- 
densed to  differences  of  one  second  in  order  to  bring  it  into 
suitable  space. 

The  original  record  showed  two  strange  peculiarities.  Almost 
invariably  the  largest  number  of  records  was  found  on  the  first 
quarter  second  after  the  even  minute,  as  20^,  21^,  etc.  ;  that  is 
to  say,  the  records  were  not  evenly  spread,  or,  as  mathematicians 


CORRELATION 


469 


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470 


TRANSMISSION 


say,  they  were  not  "  smooth,"  and  if  the  curve  were  platted  there 
would  be  an  unaccountable  "  hump  "  at  each  quarter  second. 

The  second  peculiarity  had  reference  to  the  last  record,  2  :  30. 
By  the  principle  just  stated  this  number  should  have  been  about 
70  per  cent  of  the  number  recorded  at  2  :  29^.  On  the  contrary, 
it  was  very  much  greater.  On  the  principle  running  through 
the  rest  of  the  records  we  should  predict  the  number  at  2  :  30  to 
be  about  727,  whereas  the  number  actually  recorded  is  1097, 
showing  conclusively  that  some  370  horses  had  been  admitted 
to  the  2  :  30  list  that  really  belonged  at  2  :  30^  or  slower ;  all  of 
which  shows  how  statistical  studies  bring  to  the  surface  as  noth- 
ing else  will  the  natural  irregularities  of  observations  or  whatever 
abnormal  facts  connect  themselves  with  our  investigations.  The 
table  on  page  469  is  suggestive  in  many  ways. 

RELATION  OF  SEX  AND  COLOR  TO  SPEED  AS  EXPRESSED  IN 
RATE  PER  CENT 


2:30  AND  BELOW 

2  :  15-2  :  16  AND  BELOW 

2:10-2:11  AND  BELOW 

DESCRIPTION 

Number 

Per  Cent 

Number 

Per  Cent 

Number 

Per  Cent 

Sex 

Stallions  .... 

4493 

32.0 

330 

36.0 

68 

39-o 

Geldings  .... 

3,866 

28.0 

224 

24.0 

42 

24.0 

Total  Males  .  . 

8.359 

6o.O 

554 

6o.O 

no 

63.0 

Mares    

5,520 

40.0 

361 

39-o 

66 

37-o 

Total    .... 

13.879 

9i5 

176 

Color 
Bay  . 

7,^76 

c->  o 

CO2 

CCQ 

Q2 

52  O 

Black 

i  762 

IO  O 

yt* 

IOI 

5>»y 

1  1  O 

2  C 

*•*» 

Brown  

1,885 

11  O 

I  20 

14  O 

9y 

24 

Mo 

Chestnut  .... 
Dun 

2,220 
60 

16.0 

O  A. 

126 
2 

14.0 
O  O 

25 

14.0 
O  O 

Gray 

7C2 

6.0 

46 

r  o 

4.O 

Roan  

224. 

I   r 

I  7 

y*f 

I   C. 

2  O 

••3 

*J 

1O 

Total    .... 

I3»879 

915 

I76 

From  the  table  above  it  appears  that  there  is  little  relation 
between  speed  and  either  sex  or  color.    It  is  true  that,  as  we 


CORRELATION  47 1 

read  across  the  table,  we  see  that  the  percentage  of  females  falls 
slightly  as  we  get  into  high  speeds,  but  the  fall  is  very  slight. 
The  percentages  as  to  color  vary  but  slightly,  except  in  black, 
which  decidedly  increases  with  high  speed,  and  in  gray,  which  as 
decidedly  falls  off. 

Applying  Yule's  formula  to  the  study  of  these  figures,  let  us, 
for  example,  take  the  bay  color  and  inquire  as  to  the  measure 
of  correlation  between  this  color  and  high  speed : 

Total  number  of  bays 7>376 

Number  of  bays  at  or  below  2  : 15-2  : 16 502 

Total  number  of  performers 13,879 

Total  number  of  performers  at  or  below  2  : 15-2 : 16      ,    „       915 
Number  not  bays  at  or  below  2  : 15-2 : 16  is  915  —  502  =  413 
Number  of  bays  above  2  : 15-2  : 16  is  7376  —  502  =  6874 
Number  not  bays  above  2:15-2  : 16  is  13,879 -(7376  +  413)  =  6090 

Arranging  these  values  according  to  Yule's  formula,  we  have 


BAY 

NOT  BAY 

2  :  15-2  :  16 

OR   BELOW 

502 

413 

ABOVE  2:15 

6874 

6090 

This  gives  as  a  measure  of  the  association  of  the  bay  color 
and  speed, 

6090  x  502  -  6874  x  413  =  ,  Q     g 
6090  x  502  +  6874  x  413 

While  this  result,  0.038,  shows  that  the  bays  have  furnished 
slightly  more  than  their  share  of  the  high-speed  trotters,  it  is 
doubtful  whether  this  coefficient  is  large  enough  to  enable  us  to 
assert  any  decided  correlation. 

In  much  the  same  way  exhaustive  studies  should  be  made  in  all 
lines  of  breeding,  and  at  any  expense  of  time  and  labor,  in  order 
that  we  may  possess  ourselves  of  reliable  information  in  regard 
to  as  many  details  as  possible  concerning  the  relations  of  notable 
characters  in  our  most  valuable  races. 


472  TRANSMISSION 

Summary.  Correlation  is  generally  a  relative  matter,  and 
impressions  are  exceedingly  deceptive.  Nothing  but  actual  cal- 
culation will  show  the  extent  to  which  characters  really  move 
together,  and  the  importance  of  this  knowledge  is  ample  recom- 
pense for  all  the  labor  involved.  As  will  be  seen  later,  the  same 
methods  give  us  the  only  reliable  measure  of  heredity. 

SPECIAL  EXERCISES 

Again  let  the  student  actually  do  the  work  of  finding  correlation  coeffi- 
cients until  he  acquires  facility  in  operation  and  a  distinct  conception  of 
what  is  involved. 

ADDITIONAL  REFERENCES 

CORRELATION  IN  RYE.    Experiment  Station  Record,  XIII,  241,  641. 
CORRELATION  IN  THE  PARTS  OF  CORN.    By  A.  A.  Brigham,  Gottingen. 

Experiment  Station  Record,  VIII,  486. 

CORRELATION  IN  WHEAT.    Experiment  Station  Record,  IX,  553. 
CORRELATION  MATHEMATICS.    Science,  XXII,  309-312. 
CORRELATION  OF  CHARACTERS  IN  CORN.  (German.)  Experiment  Station 

Record,  XVI,  461. 
CORRELATION  OF  SEEDS  AND  COLOR  OF   FRUIT.    Experiment  Station 

Record,  XI,  932-936. 
CORRELATION  OF  THE  MENTAL  AND  PHYSICAL  CHARACTERS  IN  MAN. 

By  Alice  Lee  and  Karl  Pearson.    Proceedings  Royal  Society,  LXXI, 

106-114. 
CORRELATION  THEORY.    Science,  XXI,  32-35. 


CHAPTER   XIV 

HEREDITY 

"  Heredity "  refers  to  the  distribution  of  racial  characters 
among  individuals  of  successive  generations.  On  the  principle 
of  heredity  all  successful  breeding  operations  depend,  and  the 
practical  breeder  needs  to  know  all  that  is  to  be  known  concern- 
ing the  manner  in  which  succeeding  generations  are  built  up  out 
of  those  characters  which  constitute  the  heritage  of  the  race. 

To  define  "  heredity "  as  the  direct   and   personal   relation 
between  the  individual  parent  and  the  individual  offspring  is 
not  only  to  restrict  its  meaning  within  too  narrow  limits  but  to 
destroy  its  significance  to  the  breeder  and  deceive  him  as  to 
the  actual  facts  of  transmission  during  descent.    "  Heredity  "      \ 
properly  refers  to  the  group  that  constitutes  the  parentage  and     . 
the  related  group  that  constitutes  the  offspring. 

All  investigations  show  that  both  groups  vary  greatly  among 
themselves,  and  to  predict  about  where,  within  the  racial  range, 
an  individual  will  fall  as  compared  with  its  personal  parent,  — 
this  is  the  object  of  a  critical  study  of  heredity,  and  the  constant 
aim  of  the  practical  breeder.  There  is  no  hope  that  the  offspring 
will  be  like  the  parent,  except  in  a  very  general  sense,  but  to 
predict  how  near  it  is  likely  to  approach  the  parent,  —  this  is 
something  that  requires  not  only  the  widest  knowledge  of  the 
ancestry  but  the  most  accurate  understanding  possible  of  the  facts 
and  principles  of  heredity.  It  is  the  purpose  now  to  inquire  some- 
what specifically  into  some  of  these  general  facts  and  principles, 

SECTION   I  — HOW  CHARACTERS  BEHAVE  IN 
TRANSMISSION 

The  particular  characters  that  associate  themselves  together, 
constituting  a  race,  variety,  or  breed,  have  separate  histories  as 
the  generations  come  and  go.  Each  has  an  identity  and  a  history 

473 


474  TRANSMISSION 

of  its  own,  and  each  establishes  and  maintains,  apparently,  fairly 
definite  relations  to  certain  of  its  associates  (correlation),  while 
with  reference  to  others  it  seems  indifferent  if  not  independent. 

Individuals  inherit  differently.  All  individuals  of  the  same 
race  possess  the  same  characters,  but  in  different  proportions, 
and  no  two  individuals,  even  from  the  same  parents,  are  alike. 
Some  portion  of  this  difference  is  of  course  due  to  development 
according  to  the  conditions  of  life,  yet  all  evidence  goes  to  show 
that,  after  full  allowance  is  made  for  this  factor,  natural  differ- 
ences exist  that  can  be  due  only  to  inheritance. 

That  each  individual  is  in  possession  of  all  the  characters  of 
the  race  is  evidenced  by  the  fact  that  his  descendants  possess 
them  and  that  he  transmits  far  more  characters  than  are  de- 
veloped sufficiently  to  be  noticeable  in  his  own  personality. 

Latent  characters.  Thus  characters  may  be  present,  but 
undeveloped,  or  "  latent."  Galton  asserts  that  latent  charac- 
ters are  "not  very  numerous";1  but  it  is  certain  that  many 
characters  may  remain  undeveloped  through  life  and  yet  be 
transmitted  perfectly.  Familiar  examples  are  the  occasional 
secretion  of  milk  by  the  male  sex,  already  alluded  to,  and 
the  transmission  of  the  milking  quality  by  bulls  as  well  as 
by  cows.  All  things  considered,  it  is  safe  to  say  that  the  visi- 
ble and  fully  developed  characters  of  an  individual  constitute 
but  a  small  proportion  of  his  real  possessions.  Especially  may 
this  be  said  of  a  highly  differentiated  race. 

Inheritance  not  limited  to  sex.  It  has  been  a  favorite  saying 
that  certain  characters  are  transmitted  to  one  sex  but  not  to  the 
other.  There  is  no  evidence  of  any  such  limitations  to  inherit- 
ance. The  limitations  of  sex  may  and  do  prevent  the  develop- 
ment of  many  characters  that  we  know  to  be  potentially  present, 
so  far  as  inheritance  is  concerned,  because  they  can  be  trans- 
mitted. In  this  respect  the  relation  of  the  male  mammal  to  milk 
secretion  is  not  different  from  that  of  the  female  that  has  never 
yet  borne  young.  The  faculty  is  latent,2  or  undeveloped,  in  both 

1  Galton,  Natural  Inheritance,  p.  187. 

2  The  term  "  latent "  is  unfortunate.    It  conveys  too  strongly  the  sense  of 
lurking.    "Undeveloped"  is  the  sense  that  ought  to  attach  to  this  unfortunate 
term  that  has  now  been  used  too  long  to  be  dislodged. 


HEREDITY  475 

cases.  They  differ  only  in  the  fact  that  with  the  female  the 
development  is  easily  brought  about,  while  in  the  male  it  is 
difficult  and  in  most  cases  impossible.1 

Belated  inheritance.  It  is  well  known  that  all  characters  do 
not  develop  contemporaneously.  Thus  the  sexual  characters 
become  developed  just  before  full  stature  is  attained,  and  with 
the  failure  of  the  primary  sexual  characters  with  advancing  age 
comes  the  development  of  many  of  the  peculiarities  of  the  other 
sex.  Then  it  is  that  the  hen  crows,  the  human  female  grows 
more  hair,  and  the  voice  of  the  male  becomes  effeminate.  The 
term  "  belated  inheritance,"  though  fixed  in  our  literature,  is 
unfortunate.  It  is  belated  development  that  is  meant.  Inheritance 
comes  only  at,  or  rather  before,  birth  ;  but  development  is  con- 
ditioned upon  many  factors,  —  among  which  age  and  sex  are 
important,  but  not  the  principal,  considerations. 

Blended  and  exclusive  inheritance.  Perhaps  the  first  and 
most  noticeable  fact  is  that  some  characters  blend  when  brought 
together  by  transmission,  while  others  remain  distinct,  being 
apparently,  mutually  exclusive.  Thus  skin  color  in  man  blends 
readily,  the  cross  between  white  and  negro  being  nearly  always 
of  some  shade  intermediate  between  those  of  the  parents,  — 
almost  never  spotted.2  In  Shorthorn  cattle  and  in  Jerseys  the 
colors  frequently,  if  not  generally,  blend,  while  in  the  Holstein- 
Friesian  they  always  remain  distinct.  In  horses  the  blend  is 
common,  but  in  hogs  it  is  practically  unknown,  so  that  in  a 
litter  of  pigs  from  a  black  and  a  white  parent  the  colors  will 
remain  distinct  ;  some  may  be  black,  some  white,  and  others 
spotted,  but  none  will  be  roans  or  grays. 

The  same  distinction  holds  as  to  characters  generally.  Some- 
times the  offspring  will  be  intermediate  between  the  parents, 
showing  a  blend  ;  and  again  it  will  resemble  one  or  the  other, 
or  else  exhibit  traces  of  both,  each  distinct  and  separate. 

For  example,  so  far  as  the  matter  has  been  studied,  the  blend 
is  most  perfect  as  to  stature,3  and  probably  as  to  size  in  general, 
but  eye  color  does  not  readily  blend,4  nor  do  "tempers"5  or 

1  The  student  is  reminded  that  milk  secretion  among  males  is  not  unknown. 

8  The  spotted  skin  is  not  absolutely  unknown  among  humans,  however. 

3  Gallon,  Natural  Inheritance,  p.  89.  *  Ibid.  p.  145.  5  Ibid.  p.  233. 


476  TRANSMISSION 

"  tastes."  This  being  true,  we  are  often  disappointed  in  trying 
to  modify  or  tone  down  a  vicious  disposition  by  mating  with 
one  of  milder  temper,  the  progeny  tending  to  follow  the  average 
of  the  race,  or  else  to  be  as  vicious  as  the  objectionable  parent. 

Particulate  inheritance,  —  inheritance  by  type,  or  bit  by  bit. 
Characters  are  often  so  closely  associated  (correlated)  as  to 
move  in  company,  so  that  whole  groups  of  characters  appear 
and  disappear  together,  even  when  there  is  little  or  no  known 
causative  relation  between  them.  Whether  this  is  merely  acci- 
dental association  of  characters  not  mutually  exclusive,  and  certain 
to  happen  occasionally  under  the  law  of  chance,  or  whether  it 
is  due,  rather,  to  some  deeper-lying  principle,  is  perhaps  uncer- 
tain ;  but  it  is  surely  true  that  man,  for  example,  runs  in  types, 
and  whoever  has  traveled  much,  or  has  enjoyed  a  fairly  exten- 
sive acquaintance,  has  met  many  people  of  no  blood  relationship, 
in  places  widely  separated,  who  yet  were  clearly  of  the  same 
type,  and  whose  similarity  became  more  evident  upon  closer 
acquaintance.1 

Clearly,  characters  are  not  altogether  independent  one  of 
another,  and  often  the  greatest  difficulty  is  encountered  in 
breaking  up  a  group,  some  members  of  which  are  desirable  and 
others  objectionable.  So  inheritance  is  often  "  bit  by  bit,"  as  if 
the  unit  of  transmission  were  larger  and  more  complex  than  the 
single  character ;  as  if  a  kind  of  permanent  partnership  were  in 
force.  The  biological  basis  of  all  this,  if  it  really  exists,  will 
probably  remain  for  a  long  time  hidden,  but  coefficients  of 
correlation  afford  at  least  a  method  for  determining  the  degree 
and  the  persistence  of  this  copartnership. 

Polymorphism  and  sexual  dimorphism.  Many  races,  instead 
of  showing  all  intermediate  gradations  from  one  extreme  to  the 
other,  in  respect  to  size  for  example,  or  color,  or  any  other 
character  or  association  of  characters,  will  exhibit  two,  three, 
or  more  forms  or  types,  so  different  and  distinct  as  often  to  be 

1  In  practical  breeding  operations  the  greatest  need  exists  for  exact  knowledge 
of  correlated  characters.  The  methods  given  in  the  preceding  chapter  enable  the 
student  to  determine  quantitatively  the  real  extent  of  correlation,  and  breeders 
should  prosecute  most  industriously  the  study  of  this  subject,  until  they  are  well 
informed  as  to  the  real  relations  of  all  valuable  characters  of  domesticated 
animals  and  plants. 


HEREDITY  477 

mistaken  for  distinct  species.  In  other  words,  their  variations 
are  not  continuous  but  discontinuous. 

Thus  the  earwig  is  of  two  distinct  types  as  to  size  (dimorphism), 
and  many  insects  exist  in  three  different  forms, — larva,  pupa, 
and  imago,  —  the  crawling  or  worm  form,  the  resting  stage,  and 
the  winged  form.1 

Sex  in  general  means  dimorphism,  for,  almost  invariably, 
marked  differences  exist  between  males  and  females  of  all 
species.  Sometimes,  as  in  most  mammals,  the  males  are  the 
larger,  but  often  the  opposite  is  true,  as  in  the  case  of  many 
birds  and  insects.  External  differences  other  than  size,  how- 
ever, are  certain  to  distinguish  the  sex  by  a  number  of  non-sexual 
characters. 

Dimorphism  in  improved  breeds.  Most  of  our  improved  breeds 
exhibit  more  than  one  type  entirely  aside  from  considerations 
of  sex.  For  example,  the  Hereford  is  remarkably  constant  in 
color,  but  there  are  two  distinct  types  as  to  form.  One  is  heavily 
built  and  long-bodied,  with  deep  flanks  and  straight  thighs ;  the 
other  is  smaller  and  shorter,  with  less  depth  behind  and  a 
tendency  to  rounded  buttocks.  The  fore  quarters  are  not  differ- 
ent in  the  two  types,  but  the  differences  behind  are  marked 
and  the  types  do  not  readily  blend.  The  breed  appears  to  be 
almost,  if  not  entirely,  dimorphic. 

Among  the  Shorthorns  we  have  no  less  than  half  a  dozen 
types  that  do  not  readily  mix.  The  pure  white  is  distinct  in  con- 
formation, as  is  the  Duchess  roan,  the  Cruickshank  roan,  the 
cherry  red,  the  dark  mahogany  red,  and  the  Cruickshank  red. 

The  Percheron  horse  is  dimorphic  both  as  to  color  and  as  to 
form.  Whether  it  will  always  remain  so,  or  will  finally  blend 
into  a  common  type  as  to  color  and  conformation,  time  only 
will  tell.  The  same  is  true  of  the  Jersey  and  the  Holstein- 
Friesian  cattle,  the  Berkshire  hogs,  and  the  Shropshire  sheep. 

All  widespread  and  most  newly  developed  breeds  are  polymor- 
phic, —  the  first  from  the  external  influences  and  different  stand- 
ards of  selection,  the  second  from  recently  associated  dissimilar 

1  Excellent  material  on  seasonal  dimorphism  of  butterflies  may  be  found  in 
Weismann,  Studies  on  the  Theory  of  Descent,  I,  i-ioo;  and  on  polymorphism  in 
insects,  Ibid.  II,  401-481. 


478  TRANSMISSION 

characters  (see  Mendel's  law).  Whether,  in  good  time,  they 
will  blend,  or  will  remain  distinct,  giving  rise  to  polymorphic 
forms  within  the  breed,  is  an  important  question  in  which  the 
breeder  is  always  deeply  interested.  If  the  polymorphism  can 
be  removed,  he  of  course  desires  to  do  it ;  if  not,  he  must  make 
the  best  of  it  and  cease  wasting  time  over  the  unattainable. 

In  all  such  cases  the  breeder  is  to  satisfy  himself  as  quickly 
as  possible  whether  the  polymorphism  is  temporary  or  perma- 
nent ;  and  if  it  be  permanent,  he  will  do  well  to  choose  the 
type  he  is  to  breed,  and  abandon  the  effort  to  blend  it  with 
another,  —  in  other  words,  he  must  be  content  to  secure  his 
results  gradually,  by  selection. 

SECTION   II  — STATISTICAL  METHODS  OF  STUDY  OF 
HEREDITY 

Until  recently  no  phase  of  evolution  has  been  so  badly  studied 
as  heredity.  The  common  mistake  has  been  to  note  a  few 
remarkable  individuals  and  exceptional  instances,  and  from 
these  attempt  to  deduce  the  "  laws  of  descent."  In  this  way 
popular  conceptions  of  heredity  have  grown  up,  many  of  which 
are  exceedingly  erroneous,  not  to  say  fantastic. 

We  have  only  recently  learned  that  studies  and  conclusions 
based  upon  individual  instances  are  worse  than  useless  because  of 
the  extreme  range  of  variability,  and  that  to  determine  the  facts 
of  heredity  with  any  degree  of  reliability,  we  must  study  the  race  as 
a  whole,  and  not  simply  the  separate  individuals  that  compose  it. 

All  this  means  that  the  laws  of  descent  are  to  be  discovered 
by  a  critical  study,  not  of  individuals,  but  of  entire  populations, 
or  at  least  of  proportions  of  populations  sufficiently  large  to  be 
safely  representative. 

Unfortunately,  the  application  of  the  statistical  method  to  the 
study  of  this  subject  is  comparatively  new,  and  as  it  is  extremely 
laborious,  the  accumulation  of  a  large  mass  of  material  will  of 
necessity  be  a  somewhat  slow  process.1 

1  Galton  was  the  first  to  apply  present-day  methods  to  the  study  of  heredity, 
but  Pearson  and  others  followed,  and  a  considerable  literature  is  accumulating, 
to  which  important  additions  are  being  rapidly  made.  The  quarterly  journal 
Riometrika  is  devoted  to  the  study  of  this  subject  by  the  statistical  method. 


HEREDITY 


479 


Unfortunately  again,  the  first  and  most  exhaustive  studies 
were  made  outside  of  our  field,  and  mostly  in  that  of  human 
characters,  so  that  the  best  material  for  the  study  of  heredity 
lies  in  this  field.  But  later  studies,  in  wider  fields,  lead  us 
confidently  to  believe  that  the  same  general  principles  control 
transmissions  everywhere,  in  all  races  and  with  all  characters. 
Accordingly  the  writer  will  employ  any  studies  that  have  been 
made,  in  whatever  fields,  that  offer  valuable  material  either  for 
elucidating  principles  or  for  illustrating  methods  of  study.  The 
fullest  data  of  all  are  those  collected  by  Galton,  dealing  princi- 
pally with  stature,  and  they  will  be  freely  employed  for  both 
purposes. 

SECTION   III— THE  REGRESSION   TABLE 

As  already  seen  (chap,  xii),  when  a  representative  popula- 
tion of  any  race  is  arranged  in  the  form  of  a  frequency  distribu- 
tion we  are  able  to  deduce  exceedingly  accurate  expressions  for 
variability. 

If  now  this  distribution  be  separated  and  assorted  according 
to  parentage,  we  shall  have  a  series  of  distributions,  each  of 
similar  parentage,  the  whole  presenting  the  best  facilities  possi- 
ble for  the  study  of  heredity.  Such  a  tabular  arrangement  con- 
stitutes what  is  called  a  "  regression  table,"  and  inasmuch  as 
all  regression  tables  present  the  same  general  features,  we  look 
upon  them  with  confidence  as  affording  reliable  data  for  the 
study  of  this  most  important  but  otherwise  most  difficult  and 
apparently  self-contradictory  subject. 

In  all  regression  tables  a  scale  of  values  (measurements, 
weights,  numerals,  or  other  valuation)  is  provided  at  one  side 
for  the  parents,  and  a  corresponding  scale  along  the  top  for  the 
offspring,  or  vice  versa.1 

The  offspring,  considered  as  adults,  is  then  distributed,  each 
individual  being  recorded  opposite  the  value  representing  his 

1  Obviously  the  parental  measurements  may  be  arranged  along  the  top  and 
those  of  the  offspring  at  the  side.  Every  observer  follows  his  fancy  in  this 
respect,  and  as  a  matter  of  fact  the  tables  are  made  in  both  ways.  The  writer 
has  become  more  accustomed  to  the  one  described  in  the  text,  and  for  no  other 
reason  prefers  to  arrange  the  parental  values  at  the  side. 


480 


TRANSMISSION 


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HEREDITY  48 1 

parent  and  in  the  column  representing  his  personal  value  as  to 
the  character  under  question.  When  completed,  such  a  table 
will  show  the  number  of  offspring  of  each  particular  value,  and 
also  the  kind  of  parents  from  which  they  sprung. 

In  whatever  direction  its  parts  are  read,  such  a  table  consists 
of  frequency  distributions  whose  means  and  standard  deviations 
may  be  determined  by  the  methods  already  given.  The  horizontals 
show  the  distribution  of  offspring  of  like  parents,  the  verticals 
show  the  range  of  parents  capable  of  producing  like  offspring, 
and  the  totals  represent  the  respective  generations. 

One  of  the  first  tables  of  this  kind  published,  and  one  of  the 
best  for  our  present  purposes,  is  the  one  on  the  preceding 
page,  from  Gal  ton,  based  on  his  studies  of  the  stature  of  Eng- 
lish people.1 

1  See  Gallon,  Natural  Inheritance,  p.  208. 

In  this  table  the  heights  were  taken  in  small  fractions,  but  recorded  in  i-inch 
groups.  For  instance,  all  measurements  falling  between  66  and  67  inches  he 
recorded  as  66.5.  In  attempting  to  do  this  for  the  sons,  however,  he  noticed  "a 
strong  bias  in  favor  of  the  integral  inches."  Hence  he  adopted  for  these 
measurements  66.2,  67.2,  etc.,  instead  of  66.5,  67.5,  etc.  As  a  matter  of  fact, 
it  makes  little  difference  what  scale  is  adopted,  provided  the  same  plan  is  always 
observed  in  the  matter  of  discarding  or  of  recording  fractions. 

One  slight  inaccuracy  for  the  individual  in  the  long  run  offsets  another,  and  as 
a  whole  such  adjustments  do  not  interfere  with  results.  Trial  calculations,  too, 
will  show  that  measurements  taken  an  inch  apart  give  substantially  the  same 
results  as  when  taken  a  half  inch  or  a  quarter  inch  apart. 

In  this  table  the  heights  of  the  adult  children  are  compared  with  the  heights 
of  the  mid-parents ;  that  is,  with  the  average  height  of  the  father  and  the  mother 
after  multiplying  the  mother's  height  by  1.08,  because  women  are,  on  the 
average,  one  twelfth  shorter  than  men.  All  female  heights  are,  therefore,  "  trans- 
formed "  and  recorded  as  male  heights.  This  custom  is  observed  in  all  statistical 
studies  involving  sex  ;  that  is,  the  female  values  are  reduced  to  their  "  male  equiv- 
alents," so  that  sex  differences  are  eliminated  from  the  mid-parent,  or,  more  prop- 
erly speaking,  everything  is  reckoned  in  terms  of  males. 

Early  in  his  studies  the  question  arose  whether  the  mid-parental  height  is  a 
safe  basis  ;  that  is  to  say,  whether  the  child  of  one  tall  and  one  short  parent  is,  in 
general,  the  same  as  the  child  of  two  parents  whose  heights  are  equal,  but  whose 
average  height  is  the  same  as  the  average  height  of  the  tall  and  the  short  parent ; 
in  other  words,  would  the  children  of  a  70-  and  a  64-inch  parent  (average  67  inches) 
be  the  same  as  one  of  two  parents  each  of  whom  is  67  inches  in  height  ? 

After  the  study  of  many  cases  Galton  found  no  difference.  He  therefore  con- 
cluded that  a  perfect  blend  takes  place  in  respect  to  stature,  and  that  the  mid- 
parental  height,  after  making  due  allowance  for  sex  differences,  may  be  safely 
taken  as  the  true  height  of  the  mid-parent  for  purposes  of  heredity  studies  (see 
Natural  Inheritance,  pp.  88-90).  We  have  since  learned  that  for  extreme  accuracy 


482 


TRANSMISSION 


It  is  not  likely  that  all  characters  behave  precisely  as  does 
stature,  —  indeed,  it  is  known  that  they  do  not ;  but  all  studies 
go  to  show  that  characters  of  every  kind  obey  the  same  general 
laws  in  descent,  and  all  regression  tables  that  have  ever  been 
prepared  exhibit  the  same  general  features.1  This  table,  there- 
fore, while  primarily  for  the  study  of  stature,  may  be  considered 
as  typical  of  regression  tables,  and  deductions  made  from  it, 
agreeing  as  they  do  with  those  made  from  all  other  similar 
tables,  whatever  the  race  or  the  character,  may  be  safely 
accepted  as  %  exhibiting  fundamental  laws  in  heredity.  Because 
all  regression  tables  afford  the  same  deductions,  they  may  be 
stated  in  the  form  of  general  principles  as  outlined  in  the 
following  sections. 

SECTION  IV  — LIKE  PARENTS  BEGET  UNLIKE  OFFSPRING 

AND,  CONVERSELY,  LIKE  OFFSPRING  MAY  BE 

BEGOTTEN  BY  UNLIKE  PARENTS 

In  this  table  the  heights  of  the  parents  are  in  the  rows  b  to  m, 
and  those  of  the  children  (as  adults)  in  the  columns  2  to  15.  It 
will  be  seen  at  once  that  the  offspring  of  parents  of  any  given 

slight  modifications  are  necessary  on  account  of  the  parental  ancestry,  but  such 
corrections  are  not  necessary  for  present  purposes. 

Gallon  calls  attention  to  an  error  in  the  first  row  of  children  and  mid-parents, 
saying  that  an  error  was  introduced  somewhere  in  the  original  tables,  which  cannot 
now  be  corrected.  "  It  is  obvious  that  four  children  cannot  have  five  mid-parents," 
he  says,  but  the  numbers  are  so  small  as  to  be  generally  discarded,  and  hence  the 
table  is  reproduced,  error  and  all.  He  adds  :  "  The  bottom  line  (fourteen  children 
with  one  mid-parent),  which  looks  suspicious,  is  correct "  (Natural  Inheritance, 
p.  208). 

In  calculations  generally  the  extremes  (above  72.5  or  73.2,  or  below  64.5  or 
63.2)  are  discarded  because  the  numbers  are  small  and  because  exact  measure- 
ments are  not  given.  In  calculating  the  general  mean,  however,  two  values  have 
been  determined,  one  without  the  extremes,  the  other  by  including  the  extremes, 
assuming  that  measurements  above  73.2  averaged  74.2,  above  72.5  averaged  73.5, 
below  64.5  averaged  63.5,  and  below  62.2  averaged  61.2.  The  assumption  is 
entirely  gratuitous,  but  it  affords  a  basis  for  using  the  extremes,  although,  as  is 
noticed,  it  makes  but  slight  difference  in  the  results. 

1  Regression  tables  may  be  prepared  for  any  character  that  can  be  measured, 
weighed,  counted,  or  in  any  way  accurately  determined.  It  only  happens  that 
studies  in  human  stature  have  been  the  most  complete  of  any,  and  are,  therefore, 
used  here. 


HEREDITY  483 

height  are  not  the  same,  but,  on  the  other  hand,  that  they  con- 
stitute a  distribution  beginning  below  the  parentage,  and  extend- 
ing to  a  considerable  distance  above  it,  with  the  largest  number 
of  individuals  near  the  middle  of  the  distribution,  close  to  but 
not  identical  with  parental  height. 

Thus  the  68  children  of  22  parents  70.5  inches  high  (row  e) 
are  distributed  from  below  62.2  to  above  73.2  inches,  a  range  of 
ii  inches,  with  the  greatest  number  (18)  slightly  below  the 
parental  height  (70.5).  Any  other  row  taken  at  random  will  show 
the  same  distribution  in  the  stature  of  the  offspring.  Heredity, 
therefore,  involves  something  besides  the  influence  of  the  imme- 
diate parent,  which,  according  to  all  studies,  seldom  exceeds  50 
per  cent  of  the  total  influence  of  the  ancestry,  leaving  the  other 
half  to  be  accounted  for  by  ancestors  farther  back.1 

Not  only  is  it  true  that  like  parents  produce  unlike  offspring, 
but  the  converse  is  also  true,  —  that  like  offspring  may  result 
from  unlike  parents.  Take  any  column  of  the  table  at  random, 
as  column  10,  containing  the  distribution  of  the  167  children  of 
the  uniform  height,  69.2  inches.  These  men  of  even  height 
were  produced  by  parents  ranging  in  stature  all  the  way  from 
72.5  inches  down  to  less  than  64.5  inches,  —  a  range  of  8 
inches.  To  be  sure,  the  parental  height  that  produced  the 
greatest  number  (48)  was  68.5  inches,  not  far  from  the  common 
height  of  the  offspring  (row  o,  column  16)  and  almost  exactly 
the  average  height  of  all  the  parents  (row  o,  column  17),  but 
the  critical  study  of  this  and  all  the  other  columns  will  clearly 
show  that  the  same  kind  of  offspring  may  be  produced  by 
greatly  different  parents. 

These  facts  show  clearly  that  two  sires  or  dams  of  equally 
favorable  appearance  may  have  sprung  from  very  different 
ancestry.  They  both  belong  to  a  distribution  covering  a  con- 
siderable range,  and  if  our  selection  is  to  be  effective  we  need 
to  know  everything  possible  of  the  entire  group  to  which  the 
prospective  parent  belongs,  or  at  least  be  intelligent  as  to  the 
portion  of  the  distribution  from  which  he  is  drawn. 

1  Every  individual  of  bisexual  parentage  has  a  total  of  2046  ancestors  within 
ten  generations.  Whether  these  ancestors  represent  that  many  different  individ- 
uals, or  whether  some  are  oft-repeated,  depends  upon  the  closeness  of  breeding. 


484  TRANSMISSION 

SECTION    V  —  REGRESSION.     IN     GENERAL,     THE    OFF- 
SPRING   IS  MORE   MEDIOCRE  THAN    THE  PARENTS; 
THAT  IS,  WHATEVER  THE  PARENTAGE,  THE  OFF- 
SPRING   EXHIBITS   A   STRONG    TENDENCY    TO 
REGRESS  TOWARD  THE  MEAN  OF  THE  RACE 

A  glance  at  any  regression  table  shows  an  uneven  distribu- 
tion of  the  population,  with  the  largest  numbers  near  the  middle 
of  the  table,  exhibiting  a  strong  tendency  to  cluster  about  the 
center.  Not  only  is  this  so,  but  if  arty  parental  row  (c  to  m)  be 
carefully  studied,  the  following  points  will  be  noted  : 

1.  The  mean  or  average  heights  of  the  children  (column  18) 
are  in  no  case  the  same  as  the  heights  of  the  parents.    Compare 
column  1 8  with  column  i. 

2.  When  the  parental  height  is  above  the  mean  of  the  race, 
that  is  to  say  68.5  inches  and  upward  (c  to  g),  then  the  mean 
height  of  the  children  is  something  less  than  the  height  of  the 
parent  (see  any  row  from  c  to  g). 

3.  But  when  the  parental  height  is  below  the  mean  of  the 
race,  — 67.5  inches  and  less  (h  to  m),  —  then  the  mean  of  the 
children  is  greater  than  the  height  of  the  parent  (see  any  row 
from  h  to  m). 

To  illustrate  :  in  row  e  are  recorded  the  heights  of  the  68 
children  of  22  mid-parents  70.5  inches  high.  In  column  18  we 
see  that  the  mean  height  of  these  68  children  was  69.5  inches, 
or  a  height  one  inch  beloiv  the  parentage,  and  by  that  much 
nearer  the  general  mean  of  the  race.  Again,  in  row  k  are 
recorded  the  various  heights  of  the  66  children  of  1 2  mid-parents 
65.5  inches  tall.  In  column  18  we  see  that  the  mean  or  average 
height  of  these  66  children  was  not  65.5  inches,  as  in  the  case 
of  the  parents,  but  66.8  inches,  or  1.3  inches  greater,  and  by  that 
much  nearer  the  general  mean  of  the  race  than  were  the  heights 
of  their  parents. 

This  principle  of  regression,  or,  as  it  is  sometimes  called,  the 
"drag  of  the  race,"  represents  the  "pull"  of  the  ancestors 
beyond  the  immediate  parents.  By  this  we  see  that,  on  the 
whole,  offspring  are  less  exceptional  than  their  parents  ;  or, 


HEREDITY  485 

stated  in  general  terms,  that  the  tendency  is  toward  mediocrity, 
and  that  offspring  are,  on  the  whole,  more  mediocre  than  their 
parents.  This  is  so  because,  in  the  absence  of  selection,  the  two 
thousand  or  more  near-by  ancestors,  all  exercising  some  influ- 
ence, were,  altogether  likely,  about  an  average  lot,  and  their 
pull  is  strong  toward  mediocrity.  With  rigid  selection  the  aver- 
age could  be  greatly  raised,  making  the  pull  higher ;  but  this 
results  simply  in  raising  the  level  of  mediocrity,  and  the  principle 
would  still  hold  ;  for  it  is  beyond  hope  or  expectation  that  these 
two  thousand  or  more  ancestors  could  #//be  held  at  a' high  level. 
This  is  why  breeders  generally  find  many  disappointments  in 
breeding  from  exceptional  individuals, — their  offspring  cannot, 
on  the  average,  be  equal  to  themselves. 

On  the  other  hand,  the  offspring  of  the  inferior  parent  is 
helped  by  the  principle  of  regression,  which  in  this  case  acts  as 
a  "  boost  "  instead  of  a  "  drag,"  J  and  we  hear  of  such  a  parent 
that  he  "  breeds  better  than  himself,"  -  all  of  which  is  a  credit 
to  the  ancestors  if  not  to  the  individual.  However,  the  children 
of  tall  parents,  while  not  so  tall  as  their  parents,  are  yet  taller 
than  the  children  of  short  parents,  giving  rise  to  the  peculiar 
form  of  the  regression  table  known  as  its  "  skew." 

This  principle  of  regression  through  the  influence  of  the 
ancestry  beyond  the  immediate  parent,  and  the  essential  medi- 
ocrity of  the  offspring  as  compared  with  the  parent,  are  then 
well  established.  This  is  not  from  any  inherent  superiority  in 
parents  or  inferiority  in  offspring,  but  from  the  fact  that  medi- 
ocrity is  the  common  condition  of  the  bulk  of  the  race. 

No  remedy  for  regression.  Nothing  but  long-continued  selec- 
tion can  ease  the  race  from  the  drag  of  regression,  and  even 
then,  and  always,  the  offspring  are  still  subject  to  the  pull  of  a 
new  but  higher  mediocrity. 

1  This  principle  is  the  salvation  of  the  "  submerged  fraction  "  of  humanity,  and  it 
is  the  principal  reason  why  so  many  successful,  even  self-made  men,  spring  from 
unpromising  parents.  It  is  entirely  possible  when  the  ancestry  has  been  only 
recently  submerged ;  it  is  hardly  possible  when  there  is  a  long  line  of  criminal  or 
defective  ancestors. 

A  distinction  is  to  be  made,  on  the  one  hand,  between  the  children  of  poor  and 
honest  parents  who  lack  advantages  but  whose  blood  lines  may  be  excellent,  and, 
on  the  other  hand,  those  whose  ancestors  have  been  submerged  for  generations ; 
very  few  of  these  rise  to  prominence,  or,  indeed,  can  rise. 


486  TRANSMISSION 

This  mediocrity  is,  therefore,  a  thing  always  to  be  reckoned 
with  by  the  breeder  who  hopes  to  attain  uniform  success  with 
improved  strains.  He  cannot  free  himself  from  its  influence. 
We  shall  see  that  its  pull  is  not  less  than  50  per  cent.  The  fail- 
ure to  know  this  fact,  and  the  willingness  to  rest  the  case  with 
the  immediate  parents  and  to  assume  that  "  like  father  like  son  " 
is  the  way  of  heredity,  or  to  accept  purity  of  blood  (pedigree)  as 
synonymous  with  uniformity  of  type,  —  this  is  the  one  fertile 
cause  of  the  greatest  failures  in  stock  breeding.  The  only  sure 
basis  of  uniform  success  lies  in  a  uniformly  excellent  ancestry 
for  at  least  five  or  six  generations  back.1  Then  the  "  drag  of 
the  race"  will  become  a  friend  and  not  an  enemy  of  improve- 
ment ;  but,  no  matter  how  excellent  the  ancestry,  it  can  never 
equal  the  exceptional  parent.  In  order  to  make  the  most  of  him, 
therefore,  this  drag  should  be  reduced  to  a  minimum. 

SECTION  VI  — THE  MEASURE  OF  HEREDITY 

Now  this  regression  is  the  pull  of  the  ancestry  back  of  the 
parent,  and  it  is  the  best  argument  for  the  fact  that  inheritance 
is  partly  from  the  race  and  not  exclusively  from  the  immediate 
parent.  Clearly,  we  need  a  measure  of  the  degree  of  resemblance 
between  the  offspring  and  the  immediate  parent,  so  that  we  may 
know  how  much  to  credit  to  the  parent  and  how  much  to  credit 
to  the  back  ancestry  through  regression.  Such  a  measure  of 
resemblance  between  mid-parent  and  offspring  will  be  a  good 
measure  of  heredity,  and  it  is  called  the  coefficient  of  heredity. 

The  coefficient  of  heredity.  Fortunately  this  involves  no  new 
conceptions  and  no  new  methods.  The  regression  table  is  noth- 
ing more  nor  less  than  a  special  form  of  correlation  table  in  which, 
instead  of  involving  two  characters  in  the  same  set  of  individuals, 
we  seek  the  correlation  between  two  sets  of  related  individuals 
with  respect  to  the  same  character. 

Thus,  in  the  table  of  statures,  we  have  in  fact  a  correlation 
table  between  mid-parents  and  sons  with  respect  to  stature,  and 
its  correlation  coefficient  (r)  2  is  for  them  a  coefficient  of  heredity. 

1  See  Law  of  Ancestral  Heredity,  sect,  xiv  of  this  chapter. 

2  The  coefficient  of  correlation  is  everywhere  denoted  by  the  letter  r. 


HEREDITY  487 

The  coefficient  of  heredity  is  therefore  nothing  more  nor  less  than 
the  correlation  coefficient  (r)  obtained  from  a  regression  table 
in  which  two  sets  of  individuals  related  by  descent  are  tabulated 
with  respect  to  the  same  character.  The  methods  of  rinding 
the  coefficient  of  heredity  are  precisely  the  same  as  those  already 
described  for  finding  the  coefficient  of  correlation ;  indeed,  the 
correlation  coefficient  of  a  regression  table  is  the  coefficient  of 
heredity. 

It  is  manifest  that  this  correlation  table  may  be  constructed 
not  only  between  mid-parents  and  offspring,  but  between  fathers 
and  sons,  between  grandfathers  and  grandsons,  between  mothers 
and  sons  (or  daughters),  between  uncles  and  nephews,  between 
brothers  and  sisters,  between  brothers  and  brothers,  and,  indeed, 
between  persons  connected  by  any  ties  of  consanguinity  what- 
ever, direct  or  indirect.  In  each  case  the  correlation  coefficient 
becomes  a  good  measure  of  hereditary  resemblance. 

If  a  regression  table  be  constructed  between  fathers  and 
mothers,  a  correlation  would  still  be  found,  though  the  two  are 
united  by  no  blood  lines  except  those  common  to  the  race  in 
general.  Such  correlation  comes  entirely  through  selection,  and 
its  coefficient  (r)  is  commonly  called  the  coefficient  of  cross 
heredity  or  "  assortative  mating."  It  is  a  good  measure  of  the 
degree  of  selection  involved  in  mating. 

The  table  on  the  next  page  gives  some  of  the  coefficients  of 
heredity  that  have  been  determined  for  different  relatives. 

Pearson  remarks  :  "  We  see  that  on  the  average  the  intensity 
of  parental  correlation  is  about  0.3  to  0.5  ;  of  grand  parental, 
about  0.15  to  0.3;  and  of  fraternal,  about  0.4  to  0.6, —  the 
latter  correlation  being  somewhat  reduced  when  the  fraternity 
consists  of  members  of  opposite  sexes." 

Regression  coefficient.  The  regression  coefficient  here  is 
computed  exactly  the  same  as  the  regression  coefficient  from 
any  other  correlation  table,  and  it  has  the  same  uses,  namely  for 
prediction  ;  that  is  to  say,  for  example,  knowing  the  deviation  of 
a  group  of  mid-parents  from  their  mean,  what  deviation  shall 
we  expect  on  the  part  of  their  offspring  ? 

The  use  of  the  word  "  regression"  in  the  term  "regression 
coefficient  "  is  likely  to  lead  to  confusion.  We  must  not  assume 


488  TRANSMISSION 

COEFFICIENTS  OF  HEREDITY  FOR  DIFFERENT  RELATIONSHIPS 


RELATIONSHIP 

MATERIAL 

CHARACTER 

CORRELATION 

Father  and  son    

English    

Stature 

"}o6 

Father  and  daughter 

English    . 

Stature 

^60 

Mother  and  son  

English    

Stature 

.JVM 

7O2 

Mother  and  daughter  .  . 

English 

Stature 

284 

Mother  and  son  
Mother  and  daughter  .  . 
Sire  and  foal  

North  American  Indians 
North  American  Indians 
Thoroughbred  horses 

Head  index 
Head  index 
Coat  color 

•370 
.300 
c  17 

Dam  and  foal 

Thoroughbred  horses 

o1/ 

(2*9 

Grandsire  and  offspring 
Grandsire  and  offspring 
Brother  and  brother    .  . 

Thoroughbred  horses  .  . 
Basset  hound     
English   

Coat  color 
Coat  color 
Stature 

o-/ 
•335 
•134 

.-JQI 

Brother  and  brother    .  . 
Colt  and  colt     
Sister  and  sister 

North  American  Indians 
Thoroughbred  horses  .  . 
English 

Head,  index 
Coat  color 
Stature 

•379 
.623 

Sister  and  sister  
Filly  and  filly 

North  American  Indians 

Head  index 

.489 

60  7 

Brother  and  sister  .... 

English 

Stature 

•uyj 

17  ^ 

Brother  and  sister  .... 
Colt  and  filly     

North  American  Indians 
Thoroughbred  horses 

Head  index 
Coat  color 

•Jl  J 
•340 

t;8T 

Whole  brethren   .  . 

Basset  hounds 

Coat  color 

O°o 

co8 

.^<_>o 

that  the  coefficient  of  regression  is  a  direct  measure  of  the  pull 
of  the  back  ancestry,  or  that  it  directly  measures  the  dissimilarity 
between  parent  and  offspring  as  shown  in  the  regression  table. 
In  fact,  we  note  that  when  regression  is  perfect,  then  the  coeffi- 
cient of  regression  is  zero ;  and  when  there  is  no  regression 
(perfect  correlation),  then  the  regression  coefficient  is  large. 
This  is  brought  out  in  the  diagram  on  the  following  page. 

This  diagram  is  a  geometrical  exhibit  of  the  regression  table 
of  statures  (page  480)  It  is  simply  a  reproduction  of  that  table, 
omitting  the  frequencies  and  putting  in  crosses  (x)  to  repre- 
sent the  means  of  the  horizontal  arrays2  (column  18). 

1  Pearson,  Grammar  of  Science,  pp.  458-460. 

2  The  mean  of  offspring  in  this  table  is  68  inches,  and  we  have  assumed  this 
value  to  be,  for  the  present  purpose,  near  enough  to  the  mean  of  mid-parents  and 
of  the  race  to  take  the  horizontal  and  vertical  lines  marked  68  as  passing  through 
the  mean  of  the  table. 


HEREDITY 


489 


If  there  were  no  regression,  that  is,  if  the  offspring  followed 
fully  the  lead  of  the  parent,  then  parents  above  the  mean  would 
have  offspring  equally  above  the  mean  ;  that  is  to  say,  parents 
69  inches  high  (one  inch  above  the  racial  mean)  would  have 
children  also  one  inch  above  the  mean,  and  parents  two  inches 
above  the  mean  would  have  children  also  two  inches  above  the 
mean,  or  70  inches  in  height.  In  this  way,  were  there  no 


62.2 

63.2 

64.2 

65.2 

Heights  of 
66.2    67.2 

Adult  Children 
68.2  69.2     70.2     71.2 

72.2 

73.2 

72.5 

P 

N/ 

/x 

M/ 

/ 

71.5 

•/ 

/ 

/ 

£70.5 

/ 

/ 

£C9.5 

x 

// 

£68.5 

1 

^67.5 
01 

A 

~ 

o 

i 

•B66.5 

K 

/ 

y 

65.5 

/ 

'  '/ 

* 

64.5 

/ 

x 

/ 

M'         N' 

FIG.  45.    Diagram  representing  regression 

regression,  these  points  would  lie  in  a  line  M'OM,  with  a  devia- 
tion of  45°  from  the  vertical. 

But  regression  is  a  fact,  and  the  children  of  /o-inch  parents 
are  not  70  inches  tall  but  something  less,  and  so  on  for  other 
values ;  so  that,  when  the  true  means  are  platted  as  calculated 
from  the  horizontal  arrays  of  the  regression  table,  and  then 
connected  by  the  best-fitting  straight  line,  this  line  Nf  ON  does 
not  coincide  with  M'OM,  as  it  would  were  there  no  regression. 
This  is  known  as  the  regression  line,  and  its  slope  is  the 
measure  of  the  pull  of  parental  heredity.  The  measure  of  this 


490  TRANSMISSION 

slope  is  our  coefficient  of  regression,  and  its  value  is  expressed 
by  the  ratio  of  /Wto  PM. 

Galton  l  finds  this  ratio,  when  dealing  with  mid-parents  and 
mid-filial  statures,  to  be  approximately  as  2  to  3  ;  "  that  is  to 
say,  the  filial  deviation  from  P  (the  common  mean)  is  on  the 
average  only  two  thirds  as  wide  as  the  mid-parental  deviation. 
I  call  this  ratio  of  2  to  3  [he  says]  the  ratio  of  '  filial  regression.' 
It  is  the  proportion  in  which  the  son  is,  on  the  average,  less 
exceptional  than  his  mid-parent."  That  is,  the  deviation  of  the 
stature  of  children  from  the  mean  of  the  race  is  only  about  two 
thirds  as  wide  as  that  of  their  mid-parents. 

[     SECTION    VII  — THE    MEAN    OF    THE    OFFSPRING    NOT 
,  NECESSARILY  THE  SAME  AS  THE  MEAN  OF 

THE   PARENTAGE 

At  first  thought  it  would  seem  axiomatic  that,  on  the  average, 
the  offspring  as  a  whole  would  be  the  same  as  the  parents, 
unless  the  race  is  undergoing  change.  In  the  table  of  statures, 
however,  by  comparing  columns  16  and  17,  row  0,  we  see  that 
the  mean  of  all  the  parents  was  68.6  inches  (not  counting  ex- 
tremes, or  68.7  inches  including  extremes),  while  the  mean  of 
the  adult  children  was  but  68. o  inches  (68.1  inches  including 
extremes).  This  indicates  a  loss  in  stature  of  over  a  half  inch 
in  a  single  generation,  unless  some  other  influence  is  at  work  to 
counteract  this  discrepancy.  That  counteracting  influences  are 
at  work  we  shall  shortly  discover,  but  the  fact  remains  that  the 
mean  of  the  offspring  is  seldom  identical  with  the  mean  of  the 
parentage.  This  fact  is  to  be  construed  as  meaning  one  (or  both) 
of  two  things,  —  either  that  the  race  is  undergoing  transforma- 
tion, or  else  that  all  grades  are  not  equally  productive. 

In  this  connection  it  is  to  be  noted,  first,  that  68.6  is  not  to 
be  taken  as  the  mean  of  the  generation  to  which  these  mid-parents 
belong  ;  that  mean  might  have  been  either  less  or  more,  because 
not  all  members  of  a  generation  become  parents,  nor  is  the 
parent  population  a  random  draft  from  the  generations  of  the 
mid-parents. 

1  Gallon,  Natural  Inheritance,  p.  97. 


HEREDITY  491 

No  fact  is  better  known  among  statisticians  than  that  wives 
differ  from  daughters  and  mothers  differ  from  wives,  —  which 
means  that  all  women  (daughters)  do  not  marry,  and  that  not 
all  wives  are  mothers  (selection) ;  that  is  to  say,  parents  are 
a  selected  draft  from  the  entire  population,  and  we  should  not 
expect  to  find  their  mean  the  same  as  that  of  their  offspring, 
which  closely  approaches  that  of  the  general  population. 

SECTION  VIII  — EXTREMES  OF  A  RACE  RELATIVELY  LESS 
PRODUCTIVE  THAN  THE  MEANS 

In  the  table  of  statures  a  strong  tendency  is  evident  toward 
increased  height  and  a  still  stronger  one  toward  decreased 
stature  (see  sect,  ix,  "  Progression  ").  This  being  true,  the  racial 
distribution  would  rapidly  spread,  if  not  entirely  divide,  into  two 
races,  giants  and  dwarfs,  unless  prevented  by  some  principle  such 
as  natural  selection.  This  principle  in  this  particular  instance  is 
evidently  relative  infertility,  a  principle  easily  deduced  in  at 
least  two  ways  : 

1 .  One  hundred  and  three  children  are  recorded  at  or  below 
64.2,  and  only  one  parent  below  64.5   (see  table  of  statures). 
Clearly  most  short  children  do  not  become  parents,  else  the  race 
would  rapidly  degenerate  as  to  size.    This  agrees  with  common 
observation,  which  is  that  dwarfs  do  not  marry.    When,  however, 
the  principle  is  applied  to  degeneracy  and  crime,  the  case  is  dif- 
ferent, for  criminals  often  produce  more  than  their  normal  ratio, 
and  many  of  their  offspring,  by  the  principle   of  progression 
(see  sect,  ix),  are  frightful  degenerates. 

To  what  extent  giants  marry  is  not  so  clearly  indicated  by 
this  table,  but  that  they  are  less  fertile  than  the  average  when 
they  do  marry  is  clearly  shown  by  comparing  columns  16  and  17. 

2.  The  average  of  fertility  in  this  table  as  a  whole  is  almost 
exactly  4^  (928  -r-  205)  per  mid-parent.    This   average  is  well 
sustained  in  the   lower  and   middle   statures,   rising   in   many 
cases  to  5  per  mid-parent  ;  but  it  rapidly  lessens  in  the  higher 
statures,  for  from   70.5   up  it  is  approximately  3.    This,  too, 
agrees  with  common  experience,  namely,  that  extremes  of  a  race 
are  generally  less  fertile  than  the  means.    Indeed,  it  is  commonly 


492  TRANSMISSION 

fertility  that  fixes  type,  unless  its  effects  happen  to  be  overcome 
by  some  other  form  of  selection ;  that  is  to  say,  the  type  of 
highest  fertility  will  become  most  numerous,  and  will  therefore 
naturally  determine  the  type  of  the  race. 

It  is  evidently  the  lessened  fertility  on  the  part  of  extremes, 
and  the  higher  breeding  powers  of  the  mediocre  individuals, 
that  in  nature  assist  selection  in  holding  the  principle  of  pro- 
gression in  check,  thus  generally,  but  not  always,  preventing 
the  splitting  up  of  races  into  smaller  varieties ;  indeed,  type  is 
mainly  the  resultant  of  relative  fertility  and  selection,  —  very 
largely  of  the  former.  This  is  why  breeders  of  highly  improved 
races  must  needs  look  well  to  fertility,  for  at  that  point  their 
first  troubles  will  arise,  all  regression  tables  indicating  that  they 
will  never  suffer  from  lack  of  variability,  as  seen  in  the  following 
section. 

SECTION  IX— PROGRESSION.    PARENTS  IN  GENERAL  PRO- 
DUCE A  FEW   INDIVIDUALS  MORE   EXTREME 
THAN  THE   RACE 

What  is  true  of  averages  is  not  necessarily  true  of  individuals 
or  of  selected  groups.  Regression  applies  to  the  mass,  not  to 
the  separate  individuals  that  compose  it.1 

Parents  in  general  produce  individuals  both  inferior  and 
superior  to  themselves,  forming  a  frequency  distribution  whose 
mean  lies  somewhere  between  that  of  the  parent  and  the  general 
mean  of  the  race.  But  the  individuals  extend  both  ways  from 
this  mean  and  some  of  them  lie  well  beyond  the  range  repre- 
sented by  the  parentage.  On  this  point  see  any  row  in  any 
regression  table,  as  row  e  in  the  table  of  statures  (page  480). 

For  example,  in  the  case  at  hand,  but  5  mid-parents,  and  pos- 
sibly only  4  (10  or  8  parents),  are  above  the  height  72.5  inches 
(see  row  £),  but  31  children  are  recorded  at  73.2  or  above  (see 
columns  14  and  15).  The  number  of  extreme  children  is  thus 
more  than  three  times  as  great  as  the  number  of  extreme 

1  For  example,  we  have  shown  that,  on  the  average,  offspring  are  more  mediocre 
than  their  parents ;  but  for  a  highly  selected  offspring  (72-inch  stature)  we  should 
find  the  parents  to  be  nearer  mediocrity  than  the  offspring. 


HEREDITY  493 

parents,  even  with  the  handicap  of  0.7  inch,  and  only  3  of  them 
were  born  of  extreme  parentage  (row  £,  column  14).  Not  only 
that,  but  the  upper  limits  of  height  in  this  table  are  decidedly 
with  the  children  rather  than  with  the  parents ;  in  other  words, 
children  can  be  found  taller  than  any  parent. 

At  the  other  extreme  of  the  table,  but  6  mid-parents  are 
recorded  at  or  below  64.5,  but  no  less  than  103  children  are 
recorded  at  64.2,  or  below. 

All  this  goes  to  show  that,  notwithstanding  the  principle  of 
regression,  the  child  population  extends  over  a  much  wider 
range  than  does  the  parental,  — a  fact  made  clearly  evident  by 
comparing  the  offspring  (row  n),  extending  from  below  62.2  to 
above  73.2,  with  the  parents  (column  17),  extending  only  from 
below  64.5  to  above  72.5.  While  neither  of  these  ranges  fixes 
the  limit,  yet  the  range  of  the  offspring  is  clearly  the  greater. 

Viewed  from  any  standpoint,  offspring  cover  a  wider  range  of 
variability  than  their  parents,  and  some  of  them  lie  quite  beyond 
the  limits  of  parentage.  This  is  progression,  and  its  effect  is, 
especially  in  the  case  of  extreme  parents,  to  send  some  indi- 
viduals not  only  beyond  the  limits  of  parents  but  well  beyond 
the  former  limits  of  the  race.  The  practical  effect  is  that  the 
population  of  any  race  can  be  moved  either  up  or  down  through 
a  large  range,  and  either  limit  extended  at  will  by  the  use  of 
highly  selected  parents. 

The  behavior  of  a  race  under  rigid  selection  and  the  operation 
of  the  principle  of  progression  are  well  illustrated  by  the  table 
on  the  next  page,  the  data  for  which  came  from  the  records  of 
ten  years  of  corn  breeding  by  Dr.  C.  G.  Hopkins,  of  the  Agri- 
cultural Experiment  Station  of  the  University  of  Illinois.  In 
these  experiments  the  purpose  was  to  influence  the  protein 
and  the  oil  content  of  corn  by  selection.  It  is  notable  in  this 
connection  that  all  four  strains,  —  high-protein,  low-protein, 
high-oil,  and  low-oil,  were  developed  from  the  same  founda- 
tion stock. 

This  table  is  taken  from  the  experiments  in  breeding  for 
increased  protein  in  corn.1  It  will  be  noted  that  the  foundation 
stock  of  corn  (1896),  mixed  ancestry,  showed  an  average  of 

1  Bulletin  No.  7/9,  Agricultural  Experiment  Station,  University  of  Illinois. 


494 


TRANSMISSION 


8   d    •  ~ 


rro<j 


O 


w      'm'o'vo      'O\'vO 


q 

II   N 


xo 


•    r^ 

«    " 


X 


HEREDITY  495 

10.92  per  cent,  with  a  mode  of  1 1,  and  an  upper  limit  (one  ear) 
of  14  per  cent, — more  accurately  13.87. 

The  result  of  one  year's  selection  made  little  evident  impres- 
sion. The  second  year's  crop  was  not  much  better.  The  mode 
was  the  same,  the  average  slightly  lower,  but  the  distribution 
became  somewhat  extended,  with  the  appearance  of  two  higher 
values  represented  by  one  ear  each. 

In  the  third  year,  with  still  better  seed  (13.06),  the  distribu- 
tion extends  still  farther,  but  the  new  value  is  down,  not  up. 
We  note,  however,  a  general  increase  of  the  higher  values,  and 
the  mode  has  moved  up  a  notch.1 

In  the  fourth  year  (1900),  with  still  better  seed  (13.74),  the 
lower  values  lessen  and  some  drop  off  entirely.  One  new  value 
appears.  All  the  upper  frequencies  are  increased ;  the  mode 
has  gone  up  two  notches,  and  we  now  have  no  less  than  28  ears 
as  good  or  better  than  the  extreme  ear  of  1896. 

The  same  principle  continues  in  1901,  which  was  an  excep- 
tionally good  year  for  protein,  and  the  theoretical  mode  goes  up 
nearly  three  points,  reaching  a  par  with  the  single  exceptional 
ear  of  the  foundation  stock.  It  so  happens  that  this  year  the 
number  of  ears  examined  was  the  same  as  that  of  the  foundation 
stock  (163),  and  of  these  ears  no  less  than  47,  or  28  per  cent,  were 
the  equal  of  the  exceptional  first  ear.  The  effects  of  selection 
settle  back  slightly  the  next  year,  but  in  the  succeeding  season 
lost  ground  is  recovered  and  there  is  produced  the  exceedingly 
exceptional  ear,  17.33,  which  has  since  proved  a  remarkable 
parent. 

The  principle  of  progression  is  still  further  illustrated  by  the 
next  table,  showing  the  effect  of  selection  both  ways.  This  is 
taken  from  Dr.  Hopkins's  original  data  in  breeding  for  high  oil 
and  for  low  oil  from  the  same  foundation  stock.  The  student 
should  note  the  decisive  manner  in  which  these  generations 
separate  themselves  from  the  foundation  stock  and  from  each 
other  as  selection  goes  on.  Nothing  could  show  more  conclu- 
sively that  under  intense  and  persistent  selection  new  values 
appear  freely  as  the  race  becomes  liberated  from  the  heavy  drag  of 

1  It  can  be  seen  by  inspection  that  the  theoretical  mode  is  not  so  high  as  the 
empirical  mode,  12. 


496 


TRANSMISSION 


2  .*- 


10  ooi 


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0  I 
col 


<        o 


NO  | 


|S  S  II  H 

as  J     a  J 


l  S  111  s  III  f  111  1  111^  f 

J     a  J     a  j     a  J     a  j     a 


HEREDITY  497 

mediocrity, — all  of  which  requires  several  years,  and  accounts 
for  the  comparatively  small  effects  of  the  first  one  or  two  years' 
selections. 

The  same  principle  is  evidently  present  and  at  work  in  stature 
(see  table,  page  480),  for  we  note  that  the  children  cover  a  wider 
range  than  do  the  parents.  It  might  seem  that  under  the  prin- 
ciple of  assortative  mating  these  exceptional  children  would  break 
away  and  establish  a  race  of  giants  and  one  of  dwarfs.  We  are 
acquainted  with  some  of  the  causes  that  prevent  this ;  namely, 
relatively  small  fertility  in  giants  (see  table)  and  lack  of  marriage 
among  dwarfs.  As  it  is,  however,  the  mean  of  stature  is  some- 
what above  the  highest  fertility  (see  table). 

It  used  to  be  said  that  the  offspring  is  a  kind  of  mean  of  the 
parentage,  and  that  the  most  that  could  be  accomplished  by 
selection  was  the  production  of  fewer  mediocre  and  inferior  and 
a  larger  proportion  of  superior  individuals.1  We  know  now,  how- 
ever, that  the  great  bulk  of  the  population  will  always  be  medio- 
cre, but  that  by  extreme  selection  we  may  secure  new  upper 
values  quite  beyond  former  limits,  not  only  of  the  parents  but 
of  the  race,  and  that  at  the  same  time  the  entire  population  ^vill 
respond  to  an  upivard  trend,  thereby  raising  the  level  of  mediocrity. 

All  experience  in  breeding  agrees  with  the  principle  here  set 
forth.  At  the  University  of  Illinois,  when  experiments  in  corn 
breeding  were  first  undertaken,  the  question  arose  whether  the 
results  of  the  first  year  or  two  were  anything  more  than  assorta- 
tive. The  effects  of  selection  were  not  at  first  pronounced, 
owing,  of  course,  to  the  "drag"  of  previous  ancestry.  But 
selection  was  extremely  rigid,  —  a  fact  which  rapidly  freed  the 
back  ancestry  from  this  drag,  —  and  with  this  came  a  decided  rise 
in  the  mean  of  the  crop ;  that  is  to  say,  the  standard  of  medioc- 
rity was  raised,  and  along  with  this  there  appeared  from  time  to 
time  occasional  ears  with  values  far  above  anything  ever  found 
in  tJie  foundation  stock.  These  were  new  values  due  to  the  prin- 
ciple of  progression,  and  the  fact  that  the  coefficient  of  variability 

1  This  position  was  always  untenable,  because,  given  the  two  best  parents  in  a 
race,  if  the  offspring  is  a  mean  between  the  two  then  no  offspring  can  ever  equal 
its  better  parent.  How  then  was  the  superior  parent  produced  ?  Such  a  doctrine 
has  but  one  outcome,  the  bringing  of  the  total  population  to  a  dead  level  of 
mediocrity. 


498  TRANSMISSION 

is  not  now  growing  less  (see  chap,  xii)  leads  to  the  conclusion 
that  the  upper  limits  in  this  breeding  experiment  will  be  set  by 
some  factor  other  than  the  failure  of  variability ;  indeed,  it  is 
the  opinion  of  the  writer  that  the  principle  of  progression  is  able 
always  to  afford  all  the  material  the  breeder  will  need,  and  that 
the  limits  of  improvement  will  be  set,  when  they  are  set,  by 
some  biological,  mechanical,  or  other  considerations  entirely 
aside  from  the  failure  of  variability  to  present  new  upper  values 
on  which  to  base  selection.1  The  remarkable  fact  about  progres- 
sion is  that  the  distributions  are  not  distorted  but  are  all  typical 
of  the  race  (see  table,  page  496). 

This  fact  of  progression  betrays  a  unique  principle  in  heredity, 
or  rather  in  variability,  because  progression  is  over  against  and 
in  spite  of  the  "  drag  of  the  race."  Those  individuals  that  have 
overleaped  the  limits  of  the  race  have  not  only  exceeded  their 
own  parents,  but  by  much  more  have  they  exceeded  the  compara- 
tive mediocrity  of  their  other  ancestors.2  Progression  cannot, 
therefore,  be  explained  by  any  principle  of  "  mean  parentage." 
It  rests  upon  a  principle  fundamentally  distinct,  and  is  to  be 
regarded  as  the  result  of  those  fortuitous  combinations  of  physio- 
logical units  which  we  may  expect  to  occur  from  time  to  time  in 
the  complicated  processes  attending  reproduction  and  differenti- 
ation, and  on  which  more  will  be  said  in  Section  XII  of  this 
chapter. 

This  suggests  what  will  be  later  found  to  be  a  fact,  namely, 
that  in  a  large  sense  heredity  follows  the  laws  of  probability,  and 
in  process  of  time  we  may  expect  all  possible  combinations  of  the 
elements  that  make  up  characters,  and  of  the  characters  that 
make  up  the  race,  the  largest  proportion  of  which  will  cluster 
about  a  common  point,  which  we  call  the  type,  but  a  few  of 
which  will  inevitably  appear  at  the  extreme  limits  of  the  range 
of  possibilities. 

1  The  greatest  menace  to  extreme  improvement  is,  as  has  already  been  said, 
lessened  fertility.    According  to  Pearson  all  evidence  points  to  the  fact  that  varia- 
bility will  never  be  reduced  by  more  than  about  1 1   per  cent.    See  Grammar  of 
Science,  p.  483. 

2  The  student  will  not  fail  to  note  that  the  ancestors  of  the  exceptional  parent 
are  of  necessity  more  mediocre  than  that  parent.    They  will  then  exert  their  influ- 
ence against,  not  in  favor  of,  progression. 


HEREDITY 


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498B 


TRANSMISSION 


The  table  given  on  page  480  and  the  deductions  therefrom  are  fully  con- 
firmed by  recent  work  done  by  Dr.  H.  L.  Rietz  in  cooperation  with  the  writer, 
as  shown  in  tabular  form  on  the  preceding  page. 

In  this  work  are  included  all  the  cows  (608  in  number)  making  1 1  pounds  or 
more  of  butter  fat  per  week  and  descended  from  dams  making  1 1  pounds  or 
more,  as  recorded  in  the  Holstein-Friesian  Advanced  Register. 

From  this  study  the  deductions  are  the  same  as  those  established  by  Gal- 
ton's  table  of  statures,  the  confirmation  being  the  more  significant  because  the 
characters  are  widely  separated,  one  being  in  man  and  the  other  in  animals, 
leading  to  the  conclusion  that  these  deductions  are  of  the  nature  of  general 
laws  of  heredity,  as  follows  : 

1 .  Dams  of  the  same  class  may  and  do  produce  a  great  variety  of  descend- 
ants.   Thus  the  ninety-four  1 4-pound  dams  (row  e)  produced  all  classes  of  cows 
from  1 1 -pound  up  to  24-pound,  although  the  greatest  number  were  1 5-pound 
and  1 6-pound  cows. 

2.  Cows  of  any  given  class  may  be  produced  by  a  great  variety  of  dams. 
Thus  the  ninety-three  1 6-pound  cows  (column  7)  were  produced  by  all  sorts  of 
dams  ranging  from  n -pound  up  to  23-pound,  all  of  which  has  but  one  mean- 
ing, namely,  that  no  direct  and  fixed  relation  exists  between  the  offspring  and 
its  immediate  or  personal  parent. 

3.  The  average  of  all  the  off  spring  (15. 31 6)  is  slightly  below  the  average  of 
the  dams  (15.368). 

•4.  For  all  dams  below  the  average  of  dams  (15.368)  the  average  of  the  off- 
spring is  above  that  of  their  dams;  but  for  dams  above  the  average,  the 
offspring  is  in  general  inferior  to  the  parentage. 

5.  Dams  of  all  classes  produced  some  offspring  that  were  inferior  to  them- 
selves and  others  that  were  superior,  and  this  is  as  true  of  dams  below  the 
average  as  well  as  of  dams  above  the  average. 

6.  Many  exceptional  cows  were  produced  by  average  dams  and  below,  but 
the  greatest  proportion  of  exceptional  cows  was  produced  by  superior  dams. 

In  comparing  this  table  with  Galton's  table  of  statures  it  must  be  borne  in 
mind  that  while  Galton's  table  of  statures  involved  little  or  no  selection,  we  are 
here  dealing  with  a  highly  selected  population  descended  from  a  single  (female) 
parent,  but  mated  with  exceptional  sires,  which,  on  the  whole,  are  superior  to 
the  dams.  It  must  also  be  borne  in  mind  that  we  do  not  have  here  the  entire 
population,  all  below  1 1  pounds  having  been  discarded ;  hence  the  fullness  of 
the  table  at  the  upper  left-hand  corner. 


HEREDITY  499 

SECTION   X— THE   EXCEPTIONAL  INDIVIDUAL  ARISES 

EITHER   FROM   MEDIOCRITY  OR  FROM  THE 

EXCEPTIONAL  PARENT 

Further  inspection  of  the  table  of  statures  shows  that  of  the 
72  children  recorded  above  six  feet  in  height  (see  columns  13, 
14,  15),  42,  or  over  one  half,  were  produced  by  mid-parents 
70.5  inches  or  under;  that  approximately  22  were  produced  by 
mid-parents  less  than  one  inch  above  the  mean  of  the  race 1 
(68.6  inches,  see  row  <?,  column  17) ;  that  no  less  than  12,  or  one 
sixth  of  all,  were  produced  by  mid-parents  recorded  at  or  below 
the  mean  of  the  race;  and  that  i  was  produced  by  a  6 5. 5 -inch 
mid-parent. 

From  this  we  see  that  exceptional  individuals  may  arise  either 
from  exceptional  or  from  mediocre  parents.  The  probability, 
however,  is  greatly  in  favor  of  the  former.  Six  72.5-inch  mid- 
parents  produced  13  exceptional  children  out  of  a  total  of  19, 
considering  everything  above  six  feet  as  exceptional.  Of  this 
number  6,  or  over  30  per  cent,  exceed  their  own  parents  in 
height.  Though  the  69. 5 -inch  mid-parents  produced  a  higher 
number  of  exceptionally  tall  children  (20),  41  parents  were 
involved  instead  of  6.  This  is  less  than  3  per  cent  of  the  total 
children  (183),  instead  of  68  per  cent,  as  in  the  case  of  the 
progeny  of  the  taller  parents. 

It  is  at  this  point  that  the  political  scientist  and  the  threm- 
matologist  recognize  different  principles.  Both  are  interested  in 
exceptional  individuals.  As  we  have  seen,  they  may  be  had 
either  from  the  general  population  or  from  a  highly  selected 
parentage.  The  breeder  chooses  the  latter  because  he  cannot 
afford  to  support  so  large  a  population  for  so  few  exceptional 
individuals.  He  takes  the  highly  selected  parentage  because 
the  proportion  of  extreme  excellence  is  higher,  and  because  its 
"drag"  is  less.  He  is  desirous  of  using  minimum  numbers  for 
economic  reasons. 

The  political  scientist  is  limited  by  no  such  considerations. 
If  he  resort  to  selection  (election)  each  time  a  ruler  is  to  be 

1  Including  only  one  half  of  the  offspring  produced  by  parents  recorded  at 
69.5- 


500 


TRANSMISSION 


chosen,  he  will  always  have  good  material  at  hand,  and,  as  he  is 
not  specially  interested  in  progeny,  he  is  not  concerned  with  the 
"drag."  What  he  wants  is  individual  service. 

If,  on  the  other  hand,  he  adopts  the  plan  of  hereditary  sover- 
eignty, he  will  deal  with  few  families  at  a  time ;  and  while,  if 
they  are  extremely  well-bred  to  begin  with,  a  large  proportion 
will  be  exceptional,  yet  a  glance  at  the  upper  lines  of  this  table 
will  be  enough  to  indicate  that  he  will  be  confronted  by  a  good 
many  hereditary  rulers  who  are  far  from  exceptional  (see  espe- 
cially row  e).  He  has  taken  a  useless  hazard,  and  this  is  the 
inevitable  handicap  of  an  hereditary  monarchy.  From  the  stand- 
point of  evolution  the  principle  is  wrong. 

The  above  ought  to  make  it  clear  why  the  breeder  and  the 
politician  should  adopt  opposite  methods.  If  service  alone  is 
wanted,  it  is  better  to  find  it  than  to  breed  it ;  and  that  is  why 
it  is  often  better  to  buy  a  particular  type  of  animal  than  to 
attempt  to  produce  it,  especially  if  the  type  is  at  all  unusual,  as 
in  the  case  of  the  "  fire  horse." 


SECTION  XI  — FRATERNAL  VARIABILITY,  — OFFSPRING 
OF  SAME  PARENTS  NOT  IDENTICAL 

The  offspring  of  like  parents  are  not  only  unlike,  but  the  suc- 
cessive offspring  of  the  same  parents  vary  widely.  The  only 
data  compiled  on  this  important  fact  are  contained  in  the  table 
on  the  following  page,  from  Galton's  studies  in  stature. 

This  table  presents  all  the  characteristics  of  the  ordinary 
regression  table  but  in  a  degree  slightly  less  pronounced.  This 
shows  that  the  same  laws  of  regression  and  progression  apply 
within  the  family  as  apply  between  families. 

Alluding  to  this  significant  fact,  Galton  remarks  : * 

It  appears  that  there  is  no  direct  hereditary  relation  between  the  personal 
parents  and  the  personal  child,  except  perhaps  through  little-known  chan- 
nels of  secondary  importance,  but  that  the  main  line  of  hereditary  connec- 
tion unites  the  sets  of  elements  out  of  which  the  personal  parents  had  been 
evolved  with  the  set  out  of  which  the  personal  child  was  evolved.  .  .  . 
This  is  why  it  is  so  important  in  hereditary  inquiry  to  deal  \t\\hfraternities 

1  Galton,  Natural  Inheritance,  pp.  19-20.    Italics  are  mine. 


HEREDITY 


501 


O         «         OOxOOO         000 


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502  TRANSMISSION 

rather  than  with  individuals,  and  with  large  fraternities  rather  than  with 
small  ones.  We  ought,  for  example,  to  compare  the  group  containing  both 
parents  and  all  the  uncles  and  aunts  with  that  containing  all  the  children. 

Here  is  the  very  gist  of  the  whole  matter,  showing  the  folly 
of  dealing  with  individuals  in  questions  of  breeding.  All  the  best 
evidence  shows  that  selection  based  upon  the  individual,  without 
regard  to  the  group  to  which  he  belongs,  will  never  result  in 
concentration  of  excellence.  It  is  only  by  persistent  selection, 
based  on  the  groups  as  a  whole  (purity  of  pedigree  in  the  sense 
of  uniformity  of  type),  that  we  shall  ever  free  even  the  family 
from  the  drag  of  the  race,  and  make  real  progress  in  improvement. 

Harold  and  Miss  Russel,  the  sire  and  dam  of  Maud  S.,  were 
owned  at  Woodburn  for  many  years,  but  of  all  their  get  only  one, 
Maud  S.,  developed  high  speed.  Why  ?  The  question  cannot  be 
answered  any  further  than  it  can  be  inferred  from  the  principle 
just  stated  and  from  the  well-known  methods  of  cleavage  of  the 
nucleus  in  cell  division  and  in  maturation ;  but  with  these  facts 
in  mind,  we  should  hardly  expect  that  two  identical  individuals 
would  ever  arise,  even  from  the  same  parents. 

The  earlier  offspring  live  longer  than  do  the  younger  children 
of  the  same  parents.  Having  established  the  fact  that  successive 
offspring  of  the  same  parents  are  different,  there  remains  the 
task  of  determining  to  what  extent  this  fraternal  variability  is 
heterogeneous,  and  to  what  extent  it  may  be  correlated  with  age 
or  with  some  similar  circumstance  that  tends  to  throw  the  off- 
spring into  a  regularly  graded  series  of  some  sort. 

On  this  point  we  know  but  little.  To  the  eye  this  variability 
appears  quite  heterogeneous,  but  studies  in  longevity,  for  ex- 
ample, have  fully  established  the  fact  that  in  man  the  older  chil- 
dren, on  the  average,  live  longer  —  that  is,  have  longer  lives  — 
than  do  the  younger  ones  of  the  same  family.  This  difference, 
as  between  the  oldest  and  the  youngest,  amounts  to  no  less  than 
four  years.1  Whether  the  same  or  a  similar  decline  takes  place 
in  other  characters  and  faculties  only  exhaustive  studies  could 
determine.  There  is  no  reason  to  doubt  that  general  principles 
apply  equally  to  man  and  to  other  animals,  excepting  in  so  far 

1  See  article  on  "  Inheritance  of  the  Duration  of  Life,"  by  Beeton  and  Pearson, 
Bioinetrika,  Vol.  I,  Part  I,  pp.  50-76. 


HEREDITY 


503 


as  social  and  other  somewhat  artificial  conditions  of  life  may 
intervene,  and  we  shall  anxiously  await  the  results  of  further 
investigation  into  the  character  and  range  of  difference  between 
offspring  of  the  same  parents. 

Individuality.  Whatever  the  results  of  investigation  in  this 
direction,  and  whatever  gradual  advance  or  decline  may  be 
established  among  the  members  of  the  same  family  on  the  aver- 
age, the  fact  remains  that  variability  is  largely  heterogeneous  as 
between  individuals,  and  that  a  marked  individuality  pervades 
all  offspring,  either  of  the  same  or  of  different  parents. 

This  lessened  deviation  between  members  of  the  same  family 
as  compared  with  descendants  in  general  is  due  to  the  fact  that, 
among  brothers,  not  only  both  immediate  parents  but  all  ances- 
tors are  identical.  The  differences  that  do  exist  within  the  same 
family  serve  to  show  the  wide  divergencies  possible  with  the  same 
hereditary  elements,  although,  in  studying  adults,  some  allow- 
ances must  always  be  made  for  differences  in  development  due 
to  external  causes.  While  members  of  the  same  family  are  in  gen- 
eral reared  more  nearly  alike  than  are  members  of  different  fam- 
ilies, yet  in  a  large  sense  every  individual  has  a  life  history  of  his 
own  quite  distinct  and  in  many  senses  different  from  that  of  any 
other  individual  of  his  own  or  of  any  other  generation.  Now  this 
life  history  affects  development  and  accounts  for  some  of  the 
differences  between  adult  individuals.  Not  all  of  the  variability 
within  a  family  can,  therefore,  be  assigned  to  hereditary  influ- 
ences, but  that  a  large  share  of  it  is  due  to  such  influences  is 
rendered  extremely  likely  by  the  well-known  fact  that  successive 
ova,  spermatozoa,  or  pollen  grains  from  the  same  individuals 
are  not  alike  either  in  their  genesis  or  in  their  behavior  after- 
ward. The  very  mechanism  of  maturation  strongly  suggests 
profound  qualitative  differences,  and  tends  to  modify  our  as- 
sumption that  all  children  of  the  same  parents  possess  identical 
hereditary  elements.  The  experience  of  breeders  everywhere  is 
that  offspring  of  the  same  individuals  are  not  slightly  different 
but  in  general  they  are  widely  different.  Whether,  and  to  what 
extent,  these  differences  can  be  lessened  by  selection  and  by 
relative  purity  of  ancestral  gametes  are  questions  on  which  light 
is  sorely  needed. 


504  TRANSMISSION 

SECTION  XII  —  CHARACTERS  TEND  TO   COMBINE  IN 
DEFINITE  MATHEMATICAL  PROPORTIONS1 

The  student  working  with  large  populations  must  be  struck 
by  the  remarkable  similarity  of  the  general  features  of  all  fre- 
quency distributions  and  arrays.  Broadly  interpreted,  this  sug- 
gests a  strong  mathematical  basis  in  reproduction. 

In  all  forms  of  life  halving  and  doubling  are  basic  processes. 
The  number  "  two,"  therefore,  as  a  mathematical  conception,  lies 
at  the  bottom  of  a  large  share  of  our  biological  problems,  espe- 
cially those  of  variability,  and  a  little  consideration  will  show 
that  the  usual  form  of  the  frequency  distribution  is  the  natural 
result  of  the  reproductive  processes,  —  indeed,  that  the  facts  of 
variability  largely,  though  not  exclusively,  follow  the  ordinary 
mathematical  laws  of  combinations  and  probabilities. 

The  mixing  of  pure  forms.  To  illustrate  this  fundamental  fact 
let  us  undertake  to  follow  the  history  of  two  characters  brought 
together  for  the  first  time,  and  the  manner  in  which  they  will 
naturally  appear  in  the  offspring. 

To  put  the  matter  in  its  simplest  form,  let  us  suppose  a  herd 
of  pure  blacks  to  meet  and  mingle  with  a  herd  (of  equal  numbers) 
of  pure  reds,  and  that  they  breed  together  without  restraint, — that 
is,  without  selection.  They  will  then  mate  indiscriminately  ;  that 
is  to  say,  a  black  female  will  mate  indifferently  with  a  black  or 
a  red  male,  —  sometimes  with  one  and  sometimes  with  the  other. 

This  being  true,  one  half  the  offspring  of  the  black  females 
will  be  pure  black  (designated  by  B**}  and  one  half  will  be  mixed, 
black  and  red  (designated  by  BR). 

The  same  principle  applies  to  the  red  females,  whose  progeny 
will,  in  like  manner,  be  equally  divided  between  the  mixed  off- 
spring and  the  pure  reds. 

Expressed  in  tabular  form  we  should  then  have  : 

For  every  200  offspring  of  black  females  100  IP  +  100  BR 

For  every  200  offspring  of  red  females          i oo  BR  +  I  oo  Rz 

Total  distribution,  400  offspring  100  Bz  +  200  BR  +  looT?2 

In  proportion  of  £2  +      2  BR  +         K* 

1  This  principle  was  first  announced  by  Quetelet,  1846,  in  Lettres  sur  la  theorie 
des  probabilites.  See  Vernon,  Variation  in  Animals  and  Plants,  p.  12. 


HEREDITY 


505 


It  is  evident  that,  whatever  the  numbers  involved,  the  above 
is  the  proportion  in  which  the  pure  and  the  mixed  forms  will 
naturally  appear  in  the  first  generation  of  admixture  between 
two  pure  forms. 

From  this  we  see  that  indiscriminate  breeding  of  distinct 
characters  results  in  both  "  pure "  and  "  crossed,"  or  mixed, 
forms  in  their  descendants,  and  this  in  the  proportion  of  1:2:  i. 
Now  this  is  a  short  "frequency  distribution,"  in  which  the 
middle  term  represents  the  individuals  of  mixed  breeding  and  is 
equal  to  the  sum  of  the  two  extremes. 

The  second  generation,  or  second  remove  from  pure  forms. 
What  now  will  be  the  character  of  the  next  generation,  as  bred 
from  the  individuals  B*  (pure  black),  BR  and  BR  (mixed),  and 
R*  (pure  red)  ? 

Continuing  the  assumption  of  indiscriminate  mating  and  uni- 
form fertility,  we  shall  have  the  following,  remembering  what 
are  the  relative  numbers  involved,  and  that  in  the  long  rtin  every 
kind  of  female  will  mate  with  every  kind  of  male,  producing 
offspring  of  the  following  character  : 

CHARACTER  OF  OFFSPRING  PRODUCED  BY  FEMALES  OF  DIFFERENT  KINDS 
WHEN  MATING  WITH  MALES  OF  DIFFERENT  KlNDS  WITHOUT  SELECTION 


FEMALES  OF  DIFFERENT  KINDS  IN  THEIR 
RELATIVE  FREQUENCY 

DIFFERENT  KINDS  OF  SIRES  IN  THEIR 
RELATIVE  FREQUENCY 

B* 

^BR 

R* 

Offspring  of  H^  mating  with 

B* 
2B*R 
B*R* 

2B*R 
4&>tf* 
zBR* 

B*JP 
zBR* 
R* 

Offspring  of  2  BR  mating  with       .... 
Offspring  of  K^  mating  with 

Total 

B*  +  4  B*R  +  6£*tf*  +  4  BR*  +  R* 

This,  then,  expressed  in  its  simplest  form  and  the  lowest 
terms,  is  the  population  resulting  from  two  generations  of  indis- 
criminate breeding  between  forms  originally  pure. 

Two  things  are  noticeable  about  this  total.  First,  it  has  all 
the  characteristics  of  the  ordinary  frequency  distribution  (i, 
4,  6,  4,  i)  ;  and,  second,  it  is  a  complete  expression  of  the 


506  TRANSMISSION 

binomial  B  +  R  expanded  to  the  fourth  power  according  to  the 
binomial  theorem. 

Succeeding  populations  follow  the  law  of  the  binomial  theorem 
except  as  interrupted  by  selection  or  differences  in  fertility.  In 
the  breeding  of  this  third  generation  inter  se  we  find  the  numbers 
becoming  rapidly  complicated,  but  from  the  fact  that  it  always 
follows  the  binomial  theorem  we  can  write  the  normal  distribu- 
tion for  the  fourth  generation  of  descendants  of  any  pair  of 
characters  as  follows  : l 

(B  +  R)*  =  B*  +  8 B~R  +  28  B^R*  +  56  B*R* 

+  70  B*R*  +  56  B*R*  +  28  B*R*  +  8  BR1  +  X*. 

Analyzing  this  "fourth-generation  population,"  we  find  : 

1.  That  no  less  than  nine  color  combinations  are  represented, 
ranging  all  the  way  from  pure  black  to  pure  red. 

2.  That  the  frequency  numbers  representing  the  various  com- 
binations, i,  8,  28,  56,  70,  56,  28,  8,  i,  form  a  symmetrical  fre- 
quency distribution  whose  total  is  256,  only  two  individuals  of 
which  are  pure. 

3.  That  future  breedings  would  become  rapidly  complicated, 
but  that  we  should  always  have  one  pure  black  and  one  pure 
red,  with  all  possible  combinations  betiveen  the  two. 

4.  That  the  actual  color  combination  of  the  individual  cannot 
in  most  cases  be  inferred  from  appearances.    For  example,  there 
is  but  one  real  black  and  but  one  real  red  in  the  whole  popula- 
tion.   However,  the  28  iPR*  will  look  like  blacks,  because  there 
have  been  six  infusions  of  black  to  but  two  of  red,  while  the 
reverse  is  true  of  another  equal  number,  28  B2J^.   The  70  B*R*, 
which  is  the  largest  number  of  all,  constituting  nearly  one  third 
of  the  entire  population,  is  equally  balanced  as  to  color  tenden- 
cies, but  will  appear  to  be  of  the  color  that  is  most  noticeable, 
—  in  this  case  probably  a  dark  red. 

Combinations  of  three  characters.  Though  the  numbers  become 
more  rapidly  complicated,  the  same  principles  apply  when 'deal- 
ing with  three  or  more  characters.  For  example,  suppose  we 
introduce  a  third  color,  white.  We  shall  then  have  as  the  result 
of  the  first  mating  the  following : 

1  The  student  can  easily  verify  these  figures  by  the  plan  already  outlined. 


HEREDITY 


507 


MALES 

B 

R 

W 

Offspring,  female  B  
Offspring,  female  R  .  .  .  .  . 
Offspring,  female  W  

£* 
BR 
BW 

BR 
R* 
RW 

BW 
RW 
W* 

Total 

B*  +  2  BR  +  R*  +  2BW+  2  RW  +  W* 

Here  we  have,  after  one  indiscriminate  mating  all  around,  a 
total  of  nine  animals,  of  which  one  is  pure  black,  one  pure  red, 
and  one  pure  white,  with  the  other  six  divided  into  three 
groups,  each  of  two  colors  combined,  —  that  is,  all  the  pos- 
sible combinations. 

If  now  this  generation  be  bred  into  itself,  new  and  strange 
combinations  are  inevitable,  giving  rise  to  a  complicated  popula- 
tion, as  follows  : 

TABLE  OF  OFFSPRING  SHOWING  THE  FOURTH  GENERATION  IN  THE 
ATTEMPT  TO  COMBINE  THREE  CHARACTERS 


DAM^ 


SIRES  OF  SAME  BREEDING  AS  DAMS 


B'* 


2  BR 


zBW 


2  WR 


2BR 

2BW 
2RW 


&JP 


2BR* 


2BR* 


2  B&  W 


2BRW* 


2BRW* 


2BW* 


4 
2RW* 


2BW* 
2RW* 


B*  +  4  B*R 
+  \2BRW* 


+  4 


12  &RW  '+ 


+  4 


+  12  BR*W 
*,—  total,  81 


Here  are  eighty-one  individuals  of  no  less  than  fifteen  differ- 
ent color  combinations,  all  effected  within  two  generations  from 
purity.  Out  of  the  eighty-one  individuals,  three,  and  three  only, 
are  as  pure  as  if  no  admixture  had  been  attempted,  suggesting 
that  a  certain  small  proportion  will  ahvays  remain  unmixed  in 
heterogeneous  breeding,  no  matter  Jiow  long  continued. 


508  TRANSMISSION 

All  the  rest  are  mixed  in  color,  no  matter  what  their  appear- 
ance. Of  these  the  4  &R  and  the  4  B*IV  will  most  likely 
appear  black,  as  will  also,  in  all  probability,  the  12  EPRW, 
because  the  B  elements  are  clearly  in  the  majority.  Similarly, 
equal  numbers  will  appear  red,  and  other  equal  numbers  will 
seem  to  be  white,  —  unless  both  colors  appear,  as  in  roans  and 
piebalds. 

There  are  three  sets  of  six  each  (6  B*R*,  6  B*W2,  and 
6R*W*)  in  which  but  two  color  elements  are  present,  but  in 
which  the  appearance  will  probably  be  fixed  by  the  color  that  is 
most  pronounced  and  which,  therefore,  tends  to  dominate  the 
other ;  thus  the  6  B^lP  will  appear  as  black  or  very  dark  red. 

Thus  it  is  that  appearances  are  often  deceiving,  and  that 
which  looks  like  a  heterogeneous  jumble  is,  after  all,  an  orderly 
collection  of  mathematically  exact  combinations.  A  scheme  like 
the  above  serves  to  show  the  exceedingly  complicated,  yet 
orderly,  systems  that  necessarily  arise  in  bisexual  reproduction, 
whatever  the  characters  involved,  —  complexity  that  increases 
rapidly,  indeed  almost  inconceivably,  as  generations  multiply. 

Because  of  these  facts  reproduction  would  be  reduced  to  a 
problem  in  probabilities,  and  we  should  have  all  possible  combi- 
nations presented,  were  it  not  for  the  fact  that  selection  is 
always  at  work  to  eliminate  certain  unfavored  forms,  and  that 
differences  in  fertility  serve  to  give  certain  combinations  still 
further  advantage  over  others.  However,  we  are  not  to  over- 
look the  fact  that,  even  though  certain  values  be  withdrawn 
from  such  a  distribution,  the  laws  of  probability  continue  to  ap- 
ply to  the  remaining  values,  whose  combinations  will  take  place 
as  before,  and  in  the  end  give  rise  to  a  distribution  not  very 
different  in  form  from  that  which  would  have  arisen  if  no 
values  had  been  removed. 

An  ultimate  confirmation  of  this  statement  is  found  in  the 
fact  that  most  frequency  distributions  are  fairly  symmetrical, 
and  that  one  large  enough  to  be  fairly  "smooth"  whatever  the 
number  of  its  terms  or  the  size  of  its  frequencies,  can  be  closely 
reproduced  by  expanding  a  binomial.  If  the  distribution  be 
symmetrical,  the  terms  of  the  binomial  should  be  numerically 
equal  (B  +  R,  or  ^  -f  |) ;  but  if  its  mode  is  not  near  the  middle 


HEREDITY 


509 


but  nearer  one  extreme,  then  the  terms  of  the  binomial  should 
be  numerically  unequal  *  (B  +  2  R  ;  ^  +  |  ;  etc.),  —  a  case  which 
would  fit  our  illustration  had  the  number  of  R  females  been 
twice  the  number  of  B  females. 

The  ease  with  which  all  distributions  can  be  fairly  well 
"  fitted  "  shows  beyond  a  doubt  that,  even  with  selection  and 
infertility  at  work,  the  final  result  is  largely  such  as  would  arise 
from  independent  probability,  —  a  fact  which  goes  to  show  that 
problems  in  heredity  are  essentially  statistical  problems. 

The  hopeless  tangle  in  which  characters  soon  become  involved 
through  bisexual  reproduction  shows  the  utter  futility  of 
attempting  to  infer  anything  whatever  from  individuals,  and 
the  almost  mathematical  certainty  of  being  able  to  detect 
almost  any  principle  or  law  of  descent  by  careful  study  of 
entire  populations. 

1  For  the  convenience'  of  the  student  the  formula  for  expanding  a  binomial 
to  any  power  is  given  here.  It  is 


(A 


1-2-3 

i  +  B". 


1-2.3.4 
This  formula  gives 

(A  +  BY  =  A*  +  2  AB  +  B* 

(A  +  B}*  =  A*  +  3  A*B  +  3  AB2  +  B* 

(A  +  £)*  =  A*  +  4  A*B  +  6  A*B*  +  4  AB*  +  B*> 

(A  +  £)*  =  A*  +  6A*£  +  isA*ff*+  20  A*B*  +  15  AW  +  6A&  +  B* 

(A  +  B)*  =  A*  +  8  A*B  +  28  A*B*  +  56  A*>B*  +  70  A*B*  +  56  A*B*> 


Thus  in  all  cases  the  coefficients  form  a  series  like  a  symmetrical  frequency 
distribution.  If,  however,  the  second  term  be  taken  as  2B,  then  the  coefficients 
will  be  substantially  altered,  forming  a  skew. 

Karl  Pearson  has  well  established  the  fact  that  frequency  distributions  obtained 
experimentally  can  often  be  fitted  better  by  the  terms  of  the  binomial  (A  +  BY 
when  n  is  not  restricted  to  be  a  positive  integer.  In  this  case  the  expansion  does 
not  terminate,  but  takes  the  general  form 


to  infinity,  in  which  the  general,  or  rth,  term  is 

n(n  -  i)(n  -  2)  •  •  •  (n  -  r  +  2)        - 


510  TRANSMISSION 

Distinctions  between  inheritance  and  development.  There  is 
still  another  reason  why  the  true  nature  of  an  individual  cannot 
always  be  detected  by  appearances,  and  this  is  found  in  the 
relative  development  of  inherited  characters. 

For  example,  suppose  that  in  the  illustration  given  on  page 
506  B  and  R  represent  size  instead  of  color.  If  B  represents 
great  size  and  R  extreme  smallness,  then,  by  all  the  principles 
of  inheritance,  the  28  B 6^?2  of  the  scheme  previously  discussed 
are  born  for  something  above  the  mean  size,  which  would  be 
represented  by  the  70  B^R^. 

Suppose,  however,  that  through  insufficient  feed  many  of 
these  individuals  fail  to  develop  the  full  size  which  is  their  birth- 
right. Such  individuals  then  appear  small,  like  the  B^R*,  or 
perhaps  even  the  R*. 

So  it  comes  about  that  these  twenty-eight  individuals,  though 
born  alike  as  to  tendencies  with  respect  to  size,  and  each  repre- 
sented by  formula  B^R*,  are  yet  very  different  when  examined 
after  development,  which  of  necessity  depends  upon  the  condi- 
tions of  life.  And  so  it  is  that,  owing  to  differences  in  develop- 
ment, relative  quality  as  we  infer  it  from  the  appearance  of  the 
adult  is  but  a  rough  and  often  misleading  indication  of  the  char- 
acters actually  present  through  inheritance.  Relative  strength 
of  characters  as  inherited  may  be  known  with  certainty  only 
through  an  intimate  knowledge  of  pedigrees.  Thus  a  buyer  of 
an  adult  animal  would  have  great  difficulty  in  selecting,  from 
appearances  only,  the  individual  born  with  greatest  tendency  to 
develop  unusual  size. 

The  mathematical  nature  of  descent  not  due  entirely  to  bisexual 
reproduction.  •  The  truth  of  this  statement  we  deduce  from  the 
fact  that  offspring  asexually  produced  vary  on  the  same  plan  as 
do  individuals  that  are  bisexually  produced.  It  is  to  be  inferred 
also  from  the  further  fact,  already  alluded  to,  that  successive 
offspring  of  the  same  parents  are  not  alike,  but  form  a  distribution 
of  the  same  general  outlines  as  that  of  the  total  population. 

This  shows  that  the  mathematical  element  in  reproduction  is 
to  be  sought  not  only  in  bisexual  union,  but  farther  back  also 
in  the  facts  of  cell  division  and  the  splitting  of  the  chromosomes, 
—  if  not  indeed  in  their  very  constitution. 


HEREDITY  5  i  i 

What  is  it  that  is  transmitted?  Evolutionary  literature  abounds 
in  such  terms  as  "  tendencies,"  "  reversion,"  "  ancestral  bias," 
and  many  others  which  imply  an  intangible  something  back  of 
the  immediate  parent.  The  common  impression  of  transmission 
is  of  something  "  handed  down,"  or  passed  on  from  one  genera- 
tion to  the  next,  and  that  the  visible  characters  represent  the 
inheritance.  It  is  evident,  however,  that  that  which  is  trans- 
mitted is  not  the  character,  but  rather  the  elements  out  of  which 
the  character  is  built  up,  and  that  these  elements  are  capable  of 
many  and  varied  combinations. 

What  these  elements  may  be  like,  and  what  the  ultimate  units 
of  variability  may  be,  —  whether  chromosomes  or  some  infinitely 
smaller  component,  — we  do  not  know.  Physiological  units  have 
not  been  discovered,  but  the  laws  under  which  they  combine  to 
form  characters,  and  under  which  the  characters  combine  to  form 
individuals  within  racial  limits, — these  have  been  sufficiently 
studied  to  warrant  the  assumption  that  they  follow  essentially 
the  ordinary  mathematical  principles  of  permutations  and  com- 
binations working  under  the  laws  of  probability.1  In  other  words, 

1  By  "combinations"  is  meant  the  number  of  different  groupings  that  can  be 
made  from  a  given  number  of  objects  without  regard  to  the  arrangement  of  the 
members.  Thus,  with  a,  b,  c,  d,  taken  three  at  a  time,  we  may  have  four  com- 
binations, namely,  abc,  abd,  acd,  bed ;  or,  taken  two  at  a  time,  we  have  six  com- 
binations, namely,  ab,  ac,  ad,  be,  bd,  cd.  Each  of  these  combinations  may  have 
two  or  more  permutations,  depending  upon  the  order  in  which  the  numbers 
stand ;  thus,  the  combination  abc  is  capable  of  the  permutations  abc,  acb,  bac,  bca^ 
cab,  cba. 

The  number  of  combinations  possible  with  a  given  number  of  units  depends 
upon  the  number  taken  in  each  grouping. 

The  general  formula  is 

n  (n  —  i)  •  •  •  (n  —  r  +  i) 
nCr'==- •> 

in  which  n  is  the  total  number  and  r  is  the  number  in  each  group. 

The  number  of  permutations,  or  different  arrangements,  possible  also  depends 
upon  the  number  in  each  group.  The  number  of  permutations  of  objects  taken 
two  at  a  time  is  «(«  -  i) ;  taken  three  at  a  time  it  is  n(n  —  i)  (n  —  2),  and  so 
on;  taken  r  at  a  time  it  is  therefore  «(«  —  i)  (n  —  2)  .  .  .  (n  —  r  +  i). 

When  all  the  numbers  enter  into  each  permutation,  then  the  formula  amounts 
to  the  multiplication  together  of  all  the  natural  numbers,  from  unity  up  to  the 
number  itself ;  that  is,  the  number  of  permutations  of  five  letters,  a,  b,  c,  d,  e,  is 
equal  to  i  x  2  x  3  X  4  X  5  =  120. 

To  give  an  illustration  of  the  probability  of  an  event,  if  a  penny  be  tossed  the 
odds  are  even  that  heads  will  be  up,  because  there  is  but  one  alternative.  This 


512  TRANSMISSION 

it  is  the  elements  of  racial  characters  that  are  transmitted,  and 
out  of  these  elements  all  possible  combinations  arise.  Some 
combinations  are  unsuited  to  the  conditions  of  life  and  others 
are  relatively  or  absolutely  infertile,  making  blank  spots  in  the 
system  which  otherwise  would  be  mathematically  complete  and 
substantially  regular. 

Even  with  these  omissions,  however,  the  distributions  into 
which  characters  fall  lend  themselves  to  ordinary  mathematical 
methods  of  study,  giving  the  strongest  ground  for  the  confident 
belief  that  the  laws  of  heredity  will  not  long  continue  to  be 
regarded  as  unexplained  mysteries,  subject  to  all  sorts  of 
exceptions  and  reversions,  but  that  characters  in  descent  will 
be  found  to  observe  as  well-defined  and  well-known  mathematical 
principles  as  do  chemical  elements  in  their  similar  but  vastly 


probability  we  express  as  \.  On  the  other  hand,  if  a  dice  be  thrown,  the  chance 
of  any  particular  side  coming  up  is  but  |,  for  there  are  six  possibilities.  If  a 
wager  be  laid  that  the  number  3  comes  up,  the  odds  will  be  five  to  one  against  it, 
for  its  chances  are  one  out  of  six.  If  two  dice  are  thrown,  the  chance  of  a  3 
coming  up  on  each  at  the  same  time  is  \  x  ^,  or  ^ ;  but  the  chance  of  two 
different  numbers,  as  3  and  4,  coming  up  together  is  doubled.  This  is  because 
the  chance  of  one  dice  turning  up  either  a  3  or  a  4  is  not  |,  but  \ ;  after  which  the 
second  dice  must  supply  the  proper  mate,  whose  chance  is  but  £,  and  \  x  \  =  y1^. 

This  means  that  in  the  long  run  this  event  will  happen  once  for  every  eighteen 
throws,  though  it  cannot  be  confidently  predicted  that  it  will  happen  on  the 
eighteenth,  the  thirty-sixth,  or  on  any  other  particular  throw. 

The  word  "  chemistry  "  has  nine  different  letters.  By  the  principle  of  permu- 
tations just  laid  down,  these  nine  letters  are  capable  of  1x2x3x4x5x6 
X  7  X  8  X  9,  or  362,880,  different  arrangements,  only  one  of  which  will  spell  the 
word  "  chemistry."  If,  therefore,  the  letters  of  this  word  should  be  tossed  into  the 
air  and  left  to  fall  into  a  groove  and  arrange  themselves  in  line  by  chance, 
the  odds  would  be  362,879  to  i  against  the  letters  taking  the  proper  arrangement 
to  spell  the  word;  but  if  the  tossing  should  be  continued,  it  is  certain  that  in 
the  long  run  they  would  fall  into  the  proper  order  to  spell  this  particular  word. 
Sooner  or  later,  therefore,  if  the  chance  differs  from  zero,  the  event  is  sure  to 
happen;  and  for  this  reason  nothing  is  more  certain  than  chance,  if  only  a 
sufficient  number  of  possibilities  be  afforded. 

The  mind  is  lost  in  the  presence  of  large  numbers,  and  the  judgment  is  con- 
fused when  the  improbable  happens,  yet  that  these  letters  would  ultimately  spell 
this  word  by  pure  chance  is  an  event  certain  to  take  place ;  not  only  is  this  so, 
but  in  the  long  run  it  will  happen  once  for  every  362,880  throws  made. 

A  little  careful  study  of  the  possible  combinations,  even  of  a  few  elements, 
and  of  the  certain  occurrence  of  possible,  even  though  improbable,  events,  will 
lead  the  student  to  work  with  variables  in  large  numbers  with  greatly  increased 
confidence. 


HEREDITY  513 

simpler  combinations.  This  is  only  another  way  of  expressing 
the  conviction  that  before  many  years  • —  if  the  present  activity 
in  statistical  studies  continues  —  the  laws  of  descent  will  be  more 
accurately  known  than  any  other  phase  of  biological  science. 
While  the  individual  will  always  be  an  uncertain  article,  as  is 
bound  to  be  the  case  where  the  element  of  chance  is  involved, 
yet  this  same  chance,  under  the  doctrine  of  probability,  becomes 
one  of  the  best  known  and  most  dependable  principles  where 
sufficiently  large  numbers  are  concerned.  Because  of  this,  the 
uncertainty  as  to  individuals  gives  way  to  the  most  definite 
knowledge  as  to  populations,  all  of  which  leads  to  the  inevitable 
conclusion  that  the  systematic  study  of  groups  of  individuals  is 
the  only  reliable  way  to  study  heredity,  and  the  only  method 
likely  to  afford  data  from  which  we  may  safely  draw  conclusions 
as  to  laws  of  descent. 

SECTION  XIII  — MENDEL'S  LAW  OF  HYBRIDS 

Mendel's  law,  as  it  is  called  from  its  original  discoverer,1 
arises  naturally  from  the  principle  outlined  in  the  last  section, 
namely,  that  characters  tend  to  combine  in  definite  proportions, 
so  that  the  natural  offspring  resulting  from  the  mating  of  two 
lines  of  parents  with  different  characters,  B  and  R,  is  of  the 
general  form  B*  +  2  BR  +  R*.  Mendel's  law  has  special  refer- 
ence to  the  apparently  crossed  portion  of  the  population  (BR)y 

1  Gregor  Johann  Mendel,  an  Austrian  monk,  and  abbot  of  Briinn,  was  born 
in  1822  and  died  in  1884.  He  carried  out  his  breeding  experiments  —  mostly 
with  peas  —  in  the  garden  of  his  cloister,  publishing  the  results  in  the  form  of  a 
few  brief  papers  in  an  obscure  journal  in  Briinn,  1853-1865.  Partly  from  the 
obscurity  of  the  journal,  but  more  from  the  fact  that  scientists  were  interested  in 
totally  different  lines  of  study,  these  papers  were  practically  lost  to  the  scientific 
world  for  more  than  thirty  years.  Upon  the  appearance  of  De  Vries'  paper  announc- 
ing the  rediscovery  and  confirmation  of  Mendel's  law  and  its  extension  to  a  great 
number  of  cases,  two  other  observers  came  forward  almost  simultaneously,  and 
independently  described  series  of  experiments  fully  confirming  Mendel's  work. 
Of  these  papers  the  first  is  that  of  Correns  (1900),  who  repeated  Mendel's 
original  experiments  with  peas  having  seed  of  different  colors.  The  second  is  a 
long  and  very  valuable  memoir  of  Tschermak,  which  gives  an  account  of  elaborate 
researches  into  the  results  of  crossing  a  number  of  varieties  of  Pisum  sativum 
(see  Mendel's  Principles  of  Heredity,  by  Bateson,  p.  14).  The  latter  experimenter 
worked  mostly  on  peas ;  Correns,  on  peas  and  corn  (maize) ;  while  De  Vries 
worked  with  many  species  and  a  great  variety  of  characters. 


514  TRANSMISSION 

and  it  aims  to  predict  the  character  of  the  offspring  when  these 
hybrids  are  bred  together. 

How  will  this  hybrid  breed?  Will  it  continue  ''pure,"  or 
will  it  break  up  into  its  component  parts  ?  This  question 
Mendel's  law  attempts  to  answer,  and  the  essence  of  the  law 
can  be  stated  in  two  propositions  : 

1.  When  crossed  forms,  or  hybrids  (BR},  are  bred  together, 
their  offspring  will  not  all  resemble  the  crossed  parents,  but  one 
fourth,  or  25  per  cent,  will  be  like  the  original  pure  parent  B, 
another  fourth  will  be  like  the  other  original  pure  parent  R,  and 
one  half,  or  50  per  cent,  will  resemble  the  crossed  forms,  so 
that  the  offspring  of  the  cross  will  tend  to  assume  the  original 
general  form  of  B2  +  2  BR  +  R*.     Of  these  the  "pure"  indi- 
viduals will  breed  as  true  as  to  the  character  in  question  as  if 
their  ancestors  had  never  been  subjected  to  crossing ;  and  the 
50  per  cent  of  crosses,  when  bred  among  themselves,  will  again 
split  up  into  pure  and  crossed  forms  in  the  proportion  of  1 :  2  :  i , 
so  that  BR  bred  with  BR  will  give  offspring  represented  by 
ip  _|_  2  BR  +  R2  indefinitely.     In  other  words,  the  offspring  of 
hybrids  will  not  all  be  hybrids,  but  they  will  assume  the  same 
general    proportions    that   are   assumed   when  pure   forms  are 
allowed  to  breed  together  indiscriminately. 

If  this  theory  be  true,  it  shows  the  impossibility  of  breeding 
a  cross  true  to  its  own  type,  on  account  of  its  innate  tendency  to 
split  up  into  its  original  pure  or  uncrossed  forms,  —  a  tendency 
which  has  long  since  been  encountered  by  breeders  ambitious 
to  fix  a  fortunate  cross,  and  which  has  gone  far  to  convince  the 
popular  mind  of  the  difficulty  in  effecting  a  real  cross. 

2.  The  second  fundamental  in  Mendel's  law  is  the  distinction 
between  dominant  and  recessive  characters.    If  the  characters 
in  question  were  evenly  ''balanced,"  and  equally  discernible, 
then  in  a  population  like  £2  +  2  BR  +  R2  the   B2  would   be 
clearly  defined,  say  black.    The  R2  would  also  be  clearly  defined, 
say  red,  and  the  2  BR  would  be  some  kind  of  blend  or  mixture 
of  the  two ;  in  other  words,  such  a  population  would  be  easily 
assorted  into  three  groups  in  the  proportion  of  1:2:1. 

On  the  other  hand,  suppose  one  character  to  be  strong  and 
easily  noted,  as  a  red  color,  or  a  strong,  heavy  stem,  while  the 


HEREDITY 


515 


other  is  extremely  delicate,  as  a  light  shade  of  blue,  easily  lost 
in  the  red,  or  a  lightness  of  foliage,  easily  obscured  by  a 
heavy  stem.1  Now,  under  circumstances  such  as  these,  the  less 
noticeable,  or  "  recessive,"  characters  will  be  visible  only  in  the 
individuals  that  are  pure  recessives,  all  others  being  dominated  by 
the  more  pronounced  character.  Thus,  if  D  stands  for  dominant 
(red  petal  or  strong  stem)  and  r  for  recessive  (light-blue  petal 
or  delicate  foliage),  then  the  actual  distribution  would  be  Z^-f- 
2  Dr  +  r2  as  before  ;  but  in  this  distribution  three  out  of  four 
individuals  would  be  distinguished  by  the  dominant  character, 
while  the  less  assertive,  the  recessive  character,  would  be  ob- 
scured except  in  the  25  per  cent  in  which  it  exists  unmixed 
with  the  dominant.  Hence  an  individual  showing  a  recessive 
character  may  be  known  at  once  to  be  pure,  but  we  cannot 
tell  by  looking  at  individuals  showing  the  dominant  character, 
which  are  pure  and  which  are  mixed.  We  know,  in  fact,  that 
we  have  both  forms  in  the  proportion  of  I  to  2,  but  in  a  case 
of  this  kind  75  per  cent  would  appear to  be  dominant,  while  only 
25  per  cent  would  appear  to  be  recessives.  In  reality,  25  per 
cent  &TQ  pure  dominants,  the  other  50  per  cent  being  apparently 
dominants,  but  actually  mixed,  —  a  fact  that  immediately  be- 
comes evident  when  they  are  bred  among  themselves,  as  they 
at  once  give  rise  to  the  characteristic  distribution,  with  the 
proper  25  percent  of  pure  recessives. 

Inasmuch  as  few  pairs  of  characters  are  equally  balanced  and 
equally  able  to  make  themselves  evident,  it  is  generally  true 
that  any  generation  from  crossed  parentage  will  show  75  per 
cent  dominant  (really  25  pure  and  50  mixed)  and  25  per  cent 
recessive,  instead  of  the  typical  25,  50,  and  25  that  would 
appear  if  the  characters  were  equally  evident  and  equally 
assertive. 

Distinction  between  characters  and  individuals.  The  reader 
will  be  misled  if  he  takes  individuals  into  consideration  here 
instead  of  characters.  The  entire  discussion  applies  to  charac- 
ters taken  singly,  and  when  we  say  of  an  individual  arising  from 
hybrid  parents  that  he  will  "  breed  pure,"  we  mean  only  as  to 

1  It  is  clear  that  only  characters  that  are  "  mutually  exclusive  "  can  be  used  in 
experimenting  on  or  illustrating  this  subject 


5i6  TRANSMISSION 

the  single  character  in  question;  for  example,  hybrids  of  Jerseys 
and  Shorthorns  would  not  breed  pure  individuals^  either  breed, 
though  pure  Jersey  and  pure  Shorthorn  characters  would  appear 
freely. 

If  we  are  to  consider  many  characters  at  once,  we  may  easily 
satisfy  ourselves  as  to  the  chances  of  an  absolutely  pure  indi- 
vidual arising  out  of  a  hybrid  ancestry. 

If  one  fourth  of  the  population  arising  from  a  hybrid  ancestry 
can  be  said  to  be  pure  as  to  a  single  character,  the  question 
arises  as  to  what  proportion  of  this  number  can  be  considered 
as  "pure"  with  respect  to  two  characters. 

From  the  fact  that  this  second  character  enjoys  the  same 
chances  as  to  purity  as  did  the  first,  we  conclude  that  one  fourth 
of  the  number,  or  one  sixteenth  of  the  whole  (|  X  J),  will  be 
pure  as  to  two  characters.  By  the  same  reasoning  we  know  that 
\  X  \  X  \  carried  to  any  number  of  terms  will  express  the  chance 
of  an  individual  being  pure  with  respect  to  the  corresponding 
number  of  characters.  If  many  characters  are  involved,  there- 
fore, the  chances  of  a  pure  individual  arising  out  of  mixed 
breeding  are  exceedingly  slight,  and  our  chance  of  being  able  to 
"  pick  him  out  "  by  his  appearance  is  still  more  remote. 

Experimental  evidence.1  It  remains  now  to  inquire  somewhat 
carefully  into  the  evidence  upon  which  these  propositions  are 
founded. 

Mendel's  first  experiments  were  conducted  with  garden  peas, 
and  covered  the  following  characters  : 2 

1 .  Differences   in  form    of  ripe   seeds,  —  either   round    and 
smooth  or  with  shallow  wrinkles,  or  else  angular  and  deeply 
wrinkled. 

2.  Differences  in  the  color  of  seed  albumen  (endosperm)  — 
either  pale  yellow,  bright  yellow,  orange,  or  green. 

3.  Differences  in  the  color  of  the  seed  coat,  —  white,  gray, 
gray  brown,  leather  brown  with  or  without  violet  spotting. 

4.  Differences   in  form  of  ripe  pod,  —  whether  inflated   or 
constricted  between  seeds. 


1  For  a  translation  of  Mendel's  original  report,  see  Bateson,  Mendel's  Prin- 
ciples of  Heredity,  pp.  40-103,  from  which  are  taken  the  data  herein  given. 

2  Ibid.  pp.  45-46. 


HEREDITY 


517 


5.  Differences  in  color  of  unripe  pods,  —  light   green,   dark 
green,  or  vividly  yellow. 

6.  Differences    in  position    of  flowers,  —  whether   axial    or 
terminal ;  that  is,  whether  distributed  along  the  main  stem  or 
bunched  at  the  top  in  a  "  false  umbel." 

7.  Differences  in  length  of  the  stem,  — varying  from  9  inches 
to  6  or  7  feet. 

It  is  perfectly  easy  to  see  that  many  of  these  characters  would 
be  dominant  over  others,  the  less  noticeable  being  "lost"  to 
view  in  the  hybrid  forms.  For  example,  dark  green  would  be 
dominant  over  light  green  and  over  most  shades  of  yellow  ;  long 
stems  over  short  ones  ;  and  dark  colors  generally  over  light  ones. 

The  preponderance  of  the  dominant  character  over  the  reces- 
sive is  so  pronounced  as  to  lead  Mendel  to  remark  that  fre- 
quently "  one  of  the  parental  characters  was  so  preponderant 
that  it  was  difficult  or  quite  impossible  to  detect  the  other  in 
the  hybrid."  In  each  of  the  seven  crosses  of  peas,  he  adds, 
"  The  hybrid  character  resembles  that  of  one  of  the  parent 
forms  so  closely  that  the  other  either  escapes  observation  com- 
pletely or  cannot  be  detected  with  certainty."  1  Of  the  charac- 
ters used,  the  following  were  found  to  be  dominant : 2 

1.  The  round  or  roundish  form  of  seed. 

2.  The  yellow  coloring  of  the  endosperm. 

3.  The  gray,  gray-brown,  or  leather-brown  color  in  the  seed 
coat. 

4.  The  inflated  over  the  constricted  pod. 

5.  The  green  color  in  the  unripe  pod. 

6.  The  distribution  of  flowers  along  the  stem. 

7.  The  greater  length  of  stem.    In  respect  to  this  point  the 
investigator  remarks  that  stems  I  foot  long  crossed  with  stems 
6  feet  long  gave  rise  to  stems  from  6  feet  to  *j\  feet  long. 

The  first,  or  hybrid,  generation.  Because  of  the  overpowering 
influence  of  the  dominant  characters,  the  "hybrid,"  or  cross, 
could  not  commonly  be  distinguished  from  the  "pure"  parent 
possessing  the  dominant  character.  This  agrees  with  the  experi- 
ence of  breeders  generally. 

1  Bateson,  Mendel's  Principles  of  Heredity,  p.  49. 

2  Ibid.  p.  50. 


TRANSMISSION 


The  second  generation,  bred  from  hybrids.  When,  however, 
these  hybrids  were  bred  among  themselves,  the  recessive  charac- 
ters came  into  evidence,  constituting  in  all  cases  approximately 
one  fourth  of  the  offspring,  leaving  the  other  75  per  cent  to  be 
apparently  dominant,  —  actually,  25  per  cent  pure  dominant  and 
50  per  cent  apparently  dominant  but  really  mixed. 

Thus,  in  Experiment  i  (as  to  form  of  seed),  from  253  hybrids 
7324  seeds  were  obtained  in  the  second  trial  year.  Among  them 
5474  were  round  or  roundish  and  1850  were  angular,  —a  ratio 
of  2.96  to  i. 

In  Experiment  2  (as  to  color  of  endosperm),  258  crossed 
plants  yielded  6022  yellow  and  2001  green,  —  a  ratio  of  3.01 
to  i. 

Distribution  of  characters.  In  each  of  these  experiments  both 
kinds  of  seed  were  usually  found  in  the  same  pod \  showing  that 
the  ovule,  and  not  the  pod,  is  the  unit.  Not  only  was  that  the 
case,  but  the  proportion  of  three  dominants  to  one  recessive 
held  only  in  the  long  run,  and  did  not  hold  for  individual  plants, 
as  is  seen  in  the  following  table  giving  the  classification  of  the 
offspring  of  the  first  ten  plants  in  each  experiment.1 


PLANTS 

EXPERIMENT  No.  i,  FORM  OF  SEED 

EXPERIMENT  No.  2,  COLOR  OF 
ENDOSPERM 

Round 

Angular 

Yellow 

Green 

x 

45 

12 

25 

II 

2 

27 

8 

32 

7 

3 

24 

7 

M 

5 

4 

T9 

10 

70 

27 

5 

32 

ii 

24 

13 

6 

26 

6 

2O 

6 

7 

88 

24 

32 

13 

8 

22 

10 

44 

9 

9 

28 

6 

50 

14 

10 

25 

7 

44 

18 

From  this  it  appears  that  the  dominant  always  exceeds  the 
recessive    in   number,    but   that   the    proportion  of    3    to    r    is 


1  Bateson,  Mendel's  Principles  of  Heredity,  p.  53. 


HEREDITY  519 

not  maintained  in  each  individual  plant.  As  to  whether  this 
comes  from  difficulties  in  identifying  and  classifying  doubtful 
specimens,  or  from  some  biological  reason,  Mendel  does  not 
express  an  opinion,  though  the  point  is  important. 

In  other  experiments  the  ratio  between  the  dominants  and 
the  recessives  was  in  all  cases  approximately  3  to  i.  In  Experi- 
ment 3  (as  to  color  of  seed  coats),  it  was  3.15  to  I  ;  in  Experi- 
ment 4  (as  to  form  of  pods),  it  was  2.95  to  i  ;  in  Experiment  5 
(as  to  color  of  unripe  pods),  it  was  2.82  to  i  ;  in  Experiment 

6  (as  to  position  of  flowers),  it  was  3. 14  to  i  ;  and  in  Experiment 

7  (as  to  length  of  stem),  it  was  2.84  to  i,  but  the  numbers  were 
relatively  small  (787  and  277)  as  compared  with  the  numbers 
involved  in  Experiments  i  and  2. 

The  third  generation,  —  second  from  hybrids.  According  to 
Mendel,1  "  those  forms  which  in  the  first  generation  maintain 
the  recessive  character  do  not  further  vary  in  the  second  genera- 
tion as  regards  this  character ;  they  remain  constant  in  their 
offspring. 

"  It  is  otherwise  with  those  which  possess  the  dominant 
character  in  the  first  generation  (bred  from  hybrids).2  Of 
these,  two  thirds  yield  offspring  which  display  the  dominant  and 
recessive  characters  in  the  proportion  of  3  to  i,  and  thereby 
show  exactly  the  same  ratio  as  the  hybrid  forms,  while  only  one 
third  remains  with  the  dominant  character  constant."  That  is 
to  say,  of  the  75  per  cent  apparent  dominants,  one  third,  or  25  per 
cent,  of  the  whole  breeds  pure  dominants,  showing  that  this 
proportion  is  actually  what  it  appears  to  be,  namely,  pure  domi- 
nants, while  two  thirds,  or  50  per  cent  of  the  whole,  yield  both 
dominants  and  recessives  in  proportion  of  3  to  i,  showing  their 
essentially  hybrid  or  crossed  nature,  and  that  their  dominance 
is  apparent  rather  than  actual.  The  separate  experiments  yielded 
ratios  as  follows  :  3 

In  Experiment  i,  among  565  plants  raised  from  round  seed 
193  yielded  round  seeds  only,  and  remained  therefore  constant 
in  this  character,  while  372  gave  both  round  and  angular  seeds  in 

1  Bateson,  Mendel's  Principles  of  Heredity,  p.  55. 

2  That  is,  with  the  75  per  cent  apparently  dominant. 

3  Bateson,  Mendel's  Principles  of  Heredity,  pp.  55-58. 


J20  TRANSMISSION 

the  proportion  of  3  to  I .  The  number  of  the  hybrids  as  compared 
with  the  constants  was  therefore  1.93  to  i.  In  Experiment  2  it 
was  2.13  to  i  ;  in  Experiments  3-7  the  numbers  were  small,  but 
approximated  the  same  ratio. 

From  this  Mendel  states  the  following  conclusion  regarding 
the  offspring  of  hybrids  l  (italics  his) : 

//  is  now  clear  that  the  hybrids  form  seeds  having  one  or  other  of  the  two 
differentiating  characters,  and  of  these  one  half  develop  again  the  hybrid 
form,  while  the  other  half  yield  plants  which  remain  constant  and  receive 
the  dominant  or  recessive  characters  (respectively)  in  equal  numbers. 

This  conclusion,  which  seems  to  be  in  accord  with  his  results, 
is  clearly  against  the  possibility  of  effecting  a  real  cross  between 
characters  that  behave  as  do  those  in  question. 

Subsequent  generations.    On  this  point  Mendel  says  : 2 

The  proportion  in  which  the  descendants  of  the  hybrids  develop  and  split 
up  in  the  first  and  second  generations  presumably  holds  good  for  all  subse- 
quent generations.  Experiments  i  and  2  have  already  been  carried  through 
six  generations,  3  and  7  through  five,  and  4,  5,  and  6  through  four  .  .  . 
and  no  departure  from  the  rule  has  been  perceptible.  The  offspring  of  the 
hybrids  separated  in  each  generation,  in  the  ratio  of  2  :  i  :  i,  into  hybrids 
and  constant  forms. 

That  is  to  say,  of  the  offspring  of  hybrids  one  fourth  resembled 
one  pure  parent  and  ever  afterward  bred  true  with  respect  to  the 
character  in  question;  one  fourth  resembled  the  other  and  also 
bred  true ;  and  one  half  still  remained  hybrid,  but  its  offspring, 
in  its  turn,  fell  apart  after  the  same  ratio  i  :  2  :  i. 

When  more  than  two  characters  are  involved.  Mendel  con- 
ducted investigations  with  plants  differing  in  a  number  of  char- 
acters simultaneously  and  concludes  as  follows  : 3 

That  the  offspring  of  the  hybrids  in  which  several  essentially  different 
characters  are  combined  represent  the  terms  of  a  series  of  combinations  in 
which  the  developmental  series  for  each  pair  of  differentiating  characters  are 
associated.  It  is  demonstrated  at  the  same  time  that  the  relation  of  each  pair 
of  different  characters  in  hybrid  union  is  independent  of  the  other  differences 
in  the  two  original  parental  stocks. 

If  ^represents  the  number  of  the  differentiating  characters  in  the  true 
original  stocks,  3"  gives  the  number  of  terms  of  the  combination  series,  4" 

1  Bateson,  Mendel's  Principles  of  Heredity,  p.  57. 

2  Ibid.  p.  57.  3  Ibid.  pp.  64-65. 


HEREDITY  521 

the  number  of  individuals  which  belong  to  the  series,  and  2"  the  number  of 
unions  which  remain  constant.  The  series  therefore  embraces,  if  the  original 
stocks  differ  in  four  characters,  3*  =  81  classes,  4*  =  256  individuals,  and 
24  =  16  constant  forms  ;  or,  which  is  the  same,  among  each  256  offspring  of 
the  hybrids  (differing  in  four  characters)  there  are  81  different  combinations, 
1 6  of  which  are  constant.1 

All  constant  combinations  which  in  peas  are  possible  by  the  combina- 
tion of  the  said  seven  differentiating  characters  were  actually  obtained  by 
repeated  crossing.  Their  number  is  given  by  27  =  128.  Thereby  is  simul- 
taneously given  the  practical  proof  that  the  constant  characters  which  appear 
in  the  several  varieties  of  a  group  of  plants  may  be  obtained  in  all  the  asso- 
ciations which  are  possible,  according  to  the  (mathematical)  laws  of  combina- 
tions, by  means  of  repeated  artificial  fertilization. 

All  this  has  a  distinct  bearing  upon  the  question  of  varieties, 
and  its  general  trend  is  that  changes  effected  by  crossing  tend 
not  to  remain  constant ;  that  is,  that  a  union  of  dissimilar  char- 
acters by  this  means  is  practically  impossible. 

It  will  be  noted  that  Mendel  makes  no  prediction  as  to  what 
hybrids  or  crossed  forms  will  look  like,  but  only  as  to  their 
"  essential  constitution  "  and  breeding  powers. 

Gametic  purity.  This  raises  the  whole  question  of  gametic 
purity  as  the  most  fundamental  question  involved  in  Mendel's 
law.  If  BR,  when  bred  with  BR,  in  actual  experience  produces 
not  more  BR's  but  rather  B2  +  2  BR  -f  R2,  then  it  raises  an 
interesting  point  as  to  the  real  nature  of  the  germs  arising  from 
the  crossed  parents  BR. 

If  the  characters  B  and  R  had  made  a  real  union,  or  blend,  in 
the  germ,  such  a  distribution  among  the  offspring  would  be 
impossible.  The  crossed  or  blended  forms  would  themselves 
breed  true,  that  is  to  their  own  type.  If  they  do  not  breed  true, 
then  we  conclude  that  the  real  cross,  or  blend,  has  not  been 
made,  and  that  in  some  way  the  characters  B  and  R  must  remain 
distinct  in  the  germinal  matter  of  the  mixed  parent ;  that  is  to 
say,  the  distribution  of  the  offspring  of  hybrid  parents  into  two 
classes,  pure  forms  and  hybrids,  instead  of  one  form  all  hybrids, 
is  possible  only  upon  the  assumption  that  the  two  characters 
remain  distinct  in  the  parents  and  in  the  germ  cells  thrown  off 
by  them,  so  that  the  elements  are  still  capable  of  uniting  under 

1  The  student  may  test  this  formula  by  making  the  complete  expansion. 
See  Bateson,  Mendel's  Principles  of  Heredity,  p.  64. 


522  TRANSMISSION 

the  law  of  chance.  This  means  that  each  parent  produces  succes- 
sively germ  cells  of  both  characters  (B  and  R},  so  that  hybrid 
forms  produce  pollen,  spermatozoa,  ova,  etc.,  of  both  original 
kinds,  which  thereafter  combine  by  the  law  of  chance ;  that  is, 
B  of  one  parent  unites  with  either  B  or  R  of  the  other,  produc- 
ing either  pure  ^'s  or  BR's  ;  and  also,  in  a  large  number  of 
instances,  some  7?' s  unite  withe's,  producing  hybrids,  and  others 
with  ^'s,  producing  pure  R's  from  hybrid  parents.  This  is  the 
theory  of  gametic  *  purity,  an  assumption  necessarily  involved  as 
a  fundamental  conception  in  Mendel's  law,  which,  in  the  opinion 
of  Mendel  himself,  applies  only  to  characters  that  do  not  blend. 

Proving  or  disproving  Mendel's  law.  A  good  many  investi- 
gators are  trying,  often  with  numbers  inadequately  small,  to 
prove  or  disprove  Mendel's  law  as  a  general  principle  of  hered- 
ity. It  may  not  be  out  of  place  to  call  the  attention  of  the 
student  to  the  uselessness  of  this  attempt,  and  to  direct  his 
attention  to  the  problems  connected  with  this  question  which 
really  call  for  further  and  much-extended  study. 

First  of  all,  Mendel's  law  as  a  general  proposition  needs  no 
further  proof.  The  experiments  on  which  it  was  founded  have 
been  carefully  repeated  by  De  Vries,  by  Correns,  and  by  Tscher- 
mak,  who  agree  as  to  the  correctness  of  his  results.  They  have 
been  repeated  upon  many  other  species,  with  uniform  results  in 
most  cases,  and  no  new  evidence  is  worth  noting  that  is  not 
founded  on  new  species  and  that  does  not  involve  relatively 
large  numbers. 

Besides  all  this,  the  fundamental  conception  of  Mendel's  law 
rests,  like  Galton's  law  of  ancestral  heredity,  upon  the  inevitable 
mathematical  relations  in  reproduction  as  outlined  in  the  previous 
section.  This  "  law  "arises,  therefore,  as  a  special  case  out  of 

1  The  term  " gamete  "  is  coming  to  be  used,  as  synonymous  with  "germ  cell," 
to  mean  the  [unfertilized  germ,  without  regard  to  sex.  When  it  is  fertilized  it  is 
spoken  of  as  a  zygote. 

Thus,  in  the  language  of  these  terms,  we  should  say  that  each  hybrid  parent 
produces  two  kinds  of  gametes,  B  and  R,  or  dominant  and  recessive,  or  whatever 
characters  have  been  combined.  Now  some  gametes  of  the  B  kind  will  unite  with 
gametes  /?,  producing  zygotes  BB  (pure) ;  others  will  unite  with  R  gametes,  pro- 
ducing zygotes  BR  (crossed) ;  and  still  other  ^gametes  will  unite  with  R  gametes, 
producing  zygotes  RR  (also  pure).  Of  mathematical  necessity,  for  an  entire  popu- 
lation these  proportions  will  be  as  i  BB  :  2  BR  :  I  RR. 


HEREDITY  523 

the  general  principle  that  the  binomial  coefficients  represent  pop- 
ulations in  general.  If  there  is  no  blend,  then  the  coefficients 
represent  the  proportions  of  distinct  character  elements.  If  a 
blend  has  occurred,  then  the  coefficients  still  represent  the  pro- 
portions within  the  blend.  There  is  and  can  be  no  uncertainty 
upon  this  feature  of  the  case.  The  dominance  of  some  characters 
over  others  is  a  matter  of  common  observation  and  may  be 
accepted  as  a  matter  of  common  sense. 

The  feature  of  Mendelism  on  which  further  light  is  needed  is 
the  matter  of  gametic  purity,  a  biological  element  of  the  prob- 
lem whose  universal  truth  is  not  yet  established,  but  which  seems 
necessary  to  a  rational  explanation  of  the  law  as  to  separation 
into  distinct  forms  ;  indeed,  Mendelism  in  its  present  form  seems 
to  mean  substantially  that  hybrid  individuals  do  not  produce 
hybrid  germs,  but  rather  that  they  produce  successively  the 
pure  germs  of  both  lines  of  parentage. 

It  maybe  considered  that  Mendel's  law  is  well  established  for 
certain  characters  ;  that  is,  for  those  that  do  not  blend.  This  may 
be,  however,  only  another  way  of  admitting  its  truth  for  those 
species  which  maintain  gametic  purity  —  those  in  whose  germs 
the  different  characters  do  not  mix  (blend),  or  in  which,  if  they 
do  mix,  the  process  is  very  slow.  This  in  turn  is  another  way 
of  saying  that  Mendel's  law  is  a  demonstrated  fact,  the  only 
unanswered  question  being,  To  what  species  and  characters 
does  it  apply  ?  and  the  answer  to  this  depends  upon  the  extent 
of  gametic  purity.  In  the  opinion  of  the  writer  this  is  the 
great  unanswered  question,  and  here  is  the  object  of  inquiry 
toward  which  all  investigation  of  Mendel's  law  should  be 
directed,  namely,  to  discover  to  what  species  and  to  what  char- 
acters its  applications  are  limited. 

Upon  this  point  it  is  worth  while  to  note  that  crossed  forms 
fall  into  one  of  three  classes,  so  far  as  appearances  are  concerned  : 
(i)  the  hybrid  may  resemble  one  of  its  "  pure "  parents  so 
closely  as  to  be  indistinguishable  from  it ;  (2)  it  may  be  a  kind 
of  intermediate  between  the  two  (different)  parents  ;  (3)  it  may 
be  quite  distinct  from  either  parent. 

Of  these  three  classes  the  first  is  clearly  Mendelian,  while  the 
second  and  third  are  doubtful,  —  the  second  exceedingly  so. 


524 


TRANSMISSION 


Both  the  second  and  third,  especially  the  former,  suggest  a 
blend,  and  there  is  much  in  the  experience  of  breeders  to  indi- 
cate that  certain  characters  do  blend,  making  a  successful  union, 
entirely  against  Mendel's  law,  whose  operations  indicate  the 
non-formation  of  stable  hybrids. 

The  writer  ventures  to  urge,  therefore,  not  the  attempt  to 
prove  or  disprove  this  great  principle,  but  the  endeavor  to  learn 
and  define  the  limits  of  its  action.  That  it  applies  to  crosses 
generally  there  is  the  greatest  reason  to  believe,  and  to  its  gen- 
eral truth  many  a  breeder  can  testify,  when  he  has  seen  some  of 
his  favorite  productions  revert  to  their  original  forms  before  his 
very  eyes. 

Experiments  in  crossing  Japanese  waltzing  mice  with  albinos.1 
Darbishire  conducted  extensive  experiments  with  this  cross, 
producing  thousands  of  individuals,  which  are  fully  classified  in 
the  original,  to  which  reference  is  here  made.  It  is  more  work 
of  this  kind  that  is  needed.  Space  forbids  giving  more  than  a 
brief  outline  of  some  of  the  more  characteristic  conclusions  of 
the  experimenter : 

1.  When  the  race  of  waltzing  mice  is  crossed  with  albino  mice  which  do 
not  waltz,  the  waltzing  habit  disappears  in  the  resulting  young,  so  that 
waltzing  is  completely  recessive  in  Mendel's  sense  ;  the  eye  color  of  the 
hybrids  is  always  dark,  the  coat  color  is  variable,  generally  a  mixture  of 
wild  gray  and  white,  —  the  character  of  the  coat  being  distinctly  correlated 
with  characters  transmitted  both  by  the  albino  and  by  the  colored  parent. 
There  is  thus  no  proper  dominance  in  Mendel's  sense,  so  far  as  eye  color 
and  coat  color  are  concerned,  the  hybrids  differing  always  in  age,  color,  and 
generally  in  coat  color,  from  both  parents. 

2.  When   the  hybrids  produced   from  the  cross  described  are  paired 
together,  the  resultant  young  exhibit  a  segregation  into  three  groups  so  far 
as  eye  color  and  coat  color  are  concerned,  into  two  so  far  as  regards  the 
waltzing  habit.    The  phenomenon  of  segregation  is  closely  similar  to  that 
described  by  Mendel  ;  and  in  color,  whether  of  eyes  or  of  fur,  the  propor- 
tions are  closely  identical  with  those  observed  by  him,  —  a  quarter  of  the 
young  resembling  their  albino  grandparents,  half  representing  their  hybrid 
parents,  and  a  quarter  resembling  their  waltzing  grandparents  in  so  far  that 
they  have  pink  eyes  and  the  same-colored  fur,  but  differing  from  any  of 
their  immediate  ancestors  in  the  range  of  coat  color  exhibited.    The  pro- 
portion of  individuals  which  exhibit  the  waltzing  habit  is  less  than  one  fifth 
of  the  whole  number  of  young,  and  is  not  a  Mendelian  proportion, 

1  Biometrika,  Vol.  Ill,  Part  I,  pp.  1-51. 


HEREDITY 

3.  When  hybrids  are  paired  with  albinos,  half  the  young  produced 
resemble  their  albino  parent,  half  resemble  their  hybrid  parent.  This  result 
is  in  accord  with  Mendel's  theory. 

Darbishire  adds  :  "There  is  no  evidence  that  any  individuals 
which  could  be  properly  described  as  '  pure  dominants'  or  *  pure 
recessives '  exist  among  the  whole  series  produced." 

The  reciprocal  cross.  In  Mendel's  experiments  generally  recip- 
rocal crosses,  according  to  all  accounts,  gave  identical  results. 
We  know  that  as  a  general  principle  this  does  not  always  hold. 
For  example,  the  common  mule,  which  is  the  product  of  the 
male  ass  and  the  female  horse,  is  said  to  be  quite  different  from 
its  reciprocal  cross,  the  hinny,  which  is  the  product  of  the  male 
horse  and  the  female  ass.  The  one  is  valuable,  while  all  horse- 
men seem  to  agree  that  the  other  is  lazy  and  worthless.  How 
much  of  this  is  fact  and  how  much  is  tradition  is  doubtless  some- 
what uncertain. 

SECTION   XIV  — THE  LAW  OF  ANCESTRAL  HEREDITY 

We  have  abundant  evidence  that  in  a  large  sense  the  off- 
spring is  the  product  of  something  more  than  the  immediate  par- 
ents. The  fact  of  resemblance  to  ancestors  more  remote  than  the 
parents,  and  the  additional  fact  that  successive  offspring  of  the 
same  parents  are  not  alike  but  form  an  array  not  very  different 
from  that  of  offspring  in  general,  —  these  facts  alone  show  us 
either  that  the  ancestors  beyond  the  parents  contribute  something 
to  the  offspring,  or  —  which  is  the  same  thing  —  that  characters 
are  made  up  out  of  elements  that  are  handed  down  from  parent 
to  offspring  and  from  which  many  and  various  combinations 
are  possible  in  succeeding  generations  and  even  in  the  same 
generation. 

The  interesting  question  now  arises,  How  are  these  hereditary 
influences  back  of  an  individual  distributed  among  his  ancestors 
of  various  degrees  of  consanguinity,  from  his  immediate  parents 
backward  ? 

Manifestly  the  answer  to  this  question  is  beset  with  many 
difficulties.  We  could  secure  a  rough  approximation  by  working 
out  the  coefficient  of  heredity  between  offspring  and  parent, 


526  TRANSMISSION 

between  offspring  and  grandparent,  and  so  on  indefinitely  ;  but 
it  would  need  to  be  done  for  each  character  separately.  This 
involves  immense  labor,  and,  moreover,  we  do  not  ordinarily 
possess  sufficiently  accurate  information  about  ancestors  back 
of  the  parent  to  enable  us  to  make  such  calculations.  We 
seek,  therefore,  some  expression  for  this  relation,  and  such 
an  expression  when  generalized  would  constitute  a  law  of 
ancestral  heredity. 

How  much  influence  belongs  to  each  separate  ancestor  ?  If 
inheritance  is  from  the  race,  or  in  a  more  particular  sense  from 
the  family  group,  then,  in  practical  breeding  affairs,  we  need  a 
measure  of  the  influence  of  each  ancestor  in  order  to  know  how 
much  importance  to  attach  to  the  parent  and  how  much  to 
attach  to  the  several  ancestors  back  of  the  parent. 

One  generation  back  the  total  heritage  rested  in  the  two 
immediate  parents,  and,  roughly  speaking,  is  to  be  regarded  as 
divisible  equally  between  them.  Two  generations  back  it  rested 
in  four  grandparents,  and,  again  waiving  considerations  of  pre- 
potency, one  fourth  of  the  heritage  came  from  each.  The  third 
generation  back  the  heritage  was  divided  among  eight  great- 
grandparents,  presumably,  on  the  average,  equally,  —  that  is, 
one  eighth  coming  from  each.  Still  another  remove,  and  no  less 
than  sixteen  great-great-grandparents  contributed  to  the  stream 
that  made  the  final  heritage,  and  it  is  fair  to  assume  that  each 
individual  contributed  its  share,  namely  one  sixteenth. 

Now  these  same  sixteen  individuals  have  contributed  also  to 
the  production  of  many  other  lines  of  descent.  If  we  had  all 
the  descendants  of  these  sixteen  great-great-grandparents  of  the 
particular  individual  we  have  in  mind,  they  would  constitute  a 
large  population,  and  we  have  no  knowledge  as  to  where,  in  their 
frequency  distribution  with  respect  to  the  character  in  question, 
our  special  individual  might  be  found.  But  of  all  the  descendants 
of  these  sixteen  great-great-grandparents  only  eight  of  the  next 
generation  contributed  to  the  production  of  the  individual  we 
have  specially  in  mind  ;  again,  in  the  next  generation,  only  four 
have  so  contributed,  and,  last  of  all,  out  of  the  large  population 
descended  from  these  sixteen  ancestors,  two  only  have  produced 
our  individual.  Now  the  law  of  ancestral  heredity  is  designed 


HEREDITY 


527 


to  enable  us  to  predict  what,  on  the  average,  should  be  the 
product  of  this  selected  ancestry. 

Inheritance  complex.  The  heritage  from  the  parent  is  not 
therefore  a  simple  thing,  but  rather  a  complex  stream,  or,  more 
properly,  two  streams  that  meet  from  different  directions,  each 
made  up  of  currents  contributed  from  many  tributaries.  How 
much  now  has  each  tributary  (ancestor)  contributed  to  the 
general  and  composite  mixture  that  we  call  the  heritage  ? 

Galton  l  made  the  first  attempt  to  answer  this  question,  and 
announced  as  the  law  of  ancestral  heredity  that  the  two  immedi- 
ate parents  contributed  between  them  one  half  (0.5)  of  the 
effective  heritage,  the  grandparents  one  fourth  (o.5)2,  the  great- 
grandparents  one  eighth  (o.5)3,  and  so  on,  so  that  the  effective 
contributions  of  the  successive  generations  would  be  represented 
by  the  fractions  \,  \,  \,  -jL,  etc.,  and  the  total  heritage  would 
be  represented  by  the  sum  of  these  fractions,  which,  extended 
to  infinity,  would  equal  I,  thus  accounting  for  the  total  heritage. 

This  general  law  applies  to  generations,  not  to  individual 
ancestors,  and  these  fractions  should  be  still  again  divided  by  the 
number  of  ancestors  in  each  generation  in  order  to  determine 
the  fractional  share  contributed  by  each  individual  ancestor. 
The  following  table  exhibits  the  fractional  contribution  of  each 
generation  and  of  each  individual  ancestor  according  to  the  law 
of  ancestral  heredity  as  stated  by  Galton. 

EFFECTIVE  HERITAGE  CONTRIBUTED  BY  EACH  GENERATION  AND  BY 

EACH  SEPARATE  ANCESTOR  ACCORDING  TO  THE  LAW  OF 

ANCESTRAL  HEREDITY  AS  STATED  BY  GALTON 


GENERATION 
BACKWARD 

EFFECTIVE  CONTRIBUTION 
OF  EACH  GENERATION 

NUMBER  OF  ANCES- 
TORS INVOLVED 

EFFECTIVE  CONTRIBUTION 
OF  Each  ANCESTOR 

I 

i  or  0.5 

2 

\  or  25.0% 

2 

i  or  (0.5)2 

4 

T^  or  6.25% 

3 

l  or  (o.5)3 

8 

&  or  i.  56  +  % 

4 

rV  or  (0.5)* 

16 

*&r  or  o-39  +  %. 

5 

A  or  (°-5)5 

32 

T*W  °r  °'°9  +  % 

1  Galton,  Natural  Inheritance,  pp.  134-137  ;  Proceedings  of  the  Royal  Society, 
LXI,  402. 


528  TRANSMISSION 

This  series  (|,  J,  J,  ^g,  etc.)  carried  to  infinity  would  account 
for  the  total  heritage,  and  if  these  fractions  are  correctly  taken 
the  influence  of  each  separate  ancestor  would,  on  the  average, 
be  represented  by  the  fractions  in  the  last  column. 

This  "  law,"  at  first  somewhat  arbitrarily  derived,  and  an- 
nounced with  considerable  hesitation,  has  received  general  sup- 
port from  later  investigations,  and  all  researches,  mathematical 
as  well  as  otherwise,  tend  to  establish  its  substantial  accuracy. 
The  first  announcement  was  based  upon  studies  in  stature. 
Somewhat  later  opportunity  was  afforded  to  make  exhaustive 
studies  from  a  large  number  of  Basset  hounds  of  distinct  colors 
and  of  several  generations  of  known  ancestry.  This  study  is 
reported  in  full  by  Galton,1  and  the  results  conform  substantially 
to  the  "  law,"  which,  as  Galton  observes,  is  "  strictly  consonant 
with  the  observed  binary  subdivisions  of  the  germ  cells,  and  the 
concomitant  extrusion  and  loss  of  one  half  of  the  several  contri- 
butions from  each  of  the  two  parents  to  the  germ  cell  of  the 
offspring."'2 

These  Basset  hounds  were  especially  favorable  for  a  study  of 
this  kind.  They  are  of  two  colors  only,  "lemon  and  white,"  or 
'they  may  be  marked  in  addition  with  a  third  color  (black),  in 
which  case  they  are  known  as  tricolor. 

It  is  said  that  individuals  are  distinctly  of  one  or  the  other 
class,  and  that  transitional  specimens  are  very  rare.  The  pedi- 
grees and  color  descriptions  had  been  carefully  kept  by  Sir 
Everett  Millais,  who  had  originated  the  particular  stock. 

Some  8i63  hounds  of  known  color  were  descended  from 
parents  of  known  color ;  in  567  3  cases  the  colors  of  the  grand- 
parents also  were  known,  and  in  188  cases  the  colors  were  known 
for  three  generations  back.  Assigning  fractional  values  to 
parents,  grandparents,  etc.,  according  to  Galton's  law  of  an- 
cestral heredity,  and  calculating  what  the  descendants  should  \>Q 
under  the  law,  it  appeared  that,  according  to  theory,  there  should 
have  been  180  tricolor  hounds  descended  from  those  whose 
ancestors  were  known  for  three  generations.  In  fact,  181  such 

1  Proceedings  of  the  Royal  Society,  LXI,  401-412.  2  Ibid.  p.  403. 

8  Not  817  and  577,  as  printed.  There  seems  to  be  an  error  of  i  in  the  first  row. 
Proceedings  of  the  Royal  Society,  LX,  409. 


HEREDITY  529 

individuals  were  found,  thus  furnishing  additional  evidence  of 
the  remarkable  agreement  between  theory  and  fact  in  matters 
of  breeding,  and  tending  strongly  to  establish  this  law. 

All  things  considered,  the  fraction  J-  seems  to  be  fairly  well 
established  as  the  ratio  of  the  intensity  with  which,  on  the 
average,  characters  are  transmitted  at  the  several  matings  in 
bisexual  reproduction ;  and  if  this  be  so,  the  law  as  stated  by 
Galton  may  be  accepted  as  substantially  correct,  especially 
when  we  recall  the  fact  that  this  (^  -f-  -J  -f  J-  +  -^Q  .  .  .  to  infinity) 
is  the  only  infinite  series  whose  ratio  is  ^  and  that  will  add  up 
to  unity,  thus  exactly  accounting  for  the  full  heritage. 

Pearson's  method.1  Pearson  has  treated  the  same  problem  by 
somewhat  more  complete  mathematical  methods,  and  arrives  at 
a  somewhat  more  general  result,  but  a  result  which  may  be  said 
to  agree  substantially  with  that  of  Galton.  He  begins  by  dealing 
with  the  question  of  biparental  inheritance.  Then  by  extending 
the  results  obtained  he  accounts  for  the  total  heritage  from  each 
generation  of  back  ancestry,  taking  into  consideration  the  vari- 
ability of  the  entire  population  to  which  each  generation  of  the 
ancestry  belongs ;  that  is,  he  considers  the  variability  of  the 
separate  generations  of  ancestors,  — a  factor  which  Galton  did 
not  take  into  account. 

Biparental  inheritance.  Starting  out  with  the  question  of  bi- 
parental inheritance,  the  problem,  stated  in  general  terms,  is 
as  follows  :  What,  on  the  average,  is  the  character  of  offspring 
of  fathers  whose  deviation  from  the  mean  of  fathers  in  general 
is  //1}  mated  with  mothers  whose  deviation  from  mothers  in 
general  is  /i2  ? 2 

In  the  discussion  of  this  problem  let  the  deviation  of  this 
offspring  from  offspring  in  general  be  //3,  and  its  standard 
deviation  (in  its  own  array)  be  denoted  by  2. 

1  Proceedings  of  the  Royal  Society,  LII,  1898,  386-412  ;  also  Pearson,  Grammar 
of  Science,  pp.  468-481. 

2  Stated  in  concrete  terms,  What  is  the  height,  on  the  average,  of  the  children 
from  those  fathers  who  are,  for  example,  two  inches  above  the  average  height  of 
fathers,  mated  with  mothers  who  are  one  and  a  half  inches  below  the  average 
height  of  mothers  ?    In  discussions  of  this  kind  the  student  should  remember  that 
males  and  females  differ  naturally  in  character  valuations,  and  also  that  not  all 
males  become  fathers  nor  all  females  become  mothers,  so  that  the  race  descends 
not  from  all  but  from  a  portion  only  of  the  preceding  generations. 


53° 


TRANSMISSION 


As  Pearson  says,  what  now  are  h%  and  2 ;  that  is,  what 
deviation  from  the  mean  of  offspring  in  general  (//3)  is  to 
be  expected  in  the  offspring  of  these  particular  parents,  and 
what  is  their  variability  or  standard  deviation  (2)  with  respect 
to  their  own  mean  ?  Cast  in  still  more  general  terms,  the 
questions  are  these  :  How  will  the  offspring  from  selected  parents 
differ  from  offspring  in  general,  and  how  will  they  differ  among 
themselves  ? 

Now  these  are  fundamental  questions  in  breeding,  and  their 
answer  involves  the  following  additional  conceptions,  all  with 
reference  to  the  character  in  question : 

1.  The  standard  deviation  for  fathers  in  general  (o-j). 

2.  The  standard  deviation  for  mothers  in  general  (<r2). 

3.  The  standard  deviation  for  offspring  in  general  (<r8). 

4.  The  coefficient  of  heredity  between  fathers  and  offspring 
reckoned  as  sons  (r^. 

5.  The  coefficient  of  heredity  between  mothers  and  offspring, 
also  reckoned  as  sons  (ra). 

6.  The    coefficient    of    correlation   (cross  heredity)   between 
fathers  and  mothers,  due  to  assortative  mating  (ra). 

Galton  considered  that  inheritance  from  two  parents  is  sub- 
stantially equivalent  to  inheritance  from  a  "  mid-parent,"  which 
should  be  the  mean  of  the  two  after  transmuting  the  female 
values  (measurements,  for  example)  into  male  equivalents  by 
multiplying  those  values  by  the  ratio  of  the  male  to  the  female 
mean,  for  the  character  in  question. 

Pearson,  on  the  other  hand,  deals  first  with  deviations,  and 
by  the  deviations  of  the  parents  from  parents  in  general  he 
attempts  to  predict  the  deviation  of  their  particular  offspring 
from  the  mean  of  offspring  in  general,  which  is  the  same  as  say- 
ing "from  the  mean  of  the  race." 

While  Galton  thus  artificially  built  up  a  mid-parent  to  take 
the  place  of  the  two  parents,  Pearson  developed  first  the  theory 
of  "  biparental  inheritance,"  taking  into  account  the  means 
and  variabilities  of  the  parents,  the  coefficient  of  assortative 
mating,  and  the  coefficient  of  correlation  between  offspring  and 
parents,  thus  leading  to  the  following  formula  for  biparental 
inheritance : 


HEREDITY  531 


Where  h^  and  //2  are  the  deviations  of  parents  from  the  mean 
of  parents  for  the  character  in  question,  ^3f  is  the  deviation  of 
the  offspring  of  these  parents  from  offspring  in  general,  vl  is 
the  standard  deviation  of  fathers  from  the  mean  of  their  gener- 
ation, cr2  is  the  standard  deviation  of  mothers  from  the  mean 
of  their  generation,  er3  is  the  standard  deviation  of  offspring  in 
general  as  to  the  character  in  question,  r±  is  the  coefficient  of 
heredity  between  offspring  and  parents  (parents  being  taken 
as  equipotent,  that  is,  making  r2  =  r^y  rs  is  the  coefficient  of 
assortative  mating. 

Now  formula  (i)  may  be  written  as  follows  : 

+-*, 

0-2 

or,  again,  it  may  be  written 
i 


(3) 

2  \        0-2 

In  this  form  the  formula  is  made  up  of  four  factors.  Of  these 
the  first  represents  the  mid-parental  deviation  ;  the  second,  the 
variability  of  mid-parents  ;  the  third,  the  correlation  coefficient 
between  mid-parent  and  offspring  ;  and  the  fourth,  the  standard 
deviation  for  this  particular  character.  If,  now,  each  of  these 
factors  (except  cr3)  be  represented  by  a  single  letter,  we  have 
the  following  : 

H  =  -  (  AI  +  —  ^2  1  =  the  mid-parental  deviation, 

2    \  0-2         / 

S  I  =  —  -  •=  —  -  =  the  variability  of  mid-parents, 

V2 
T    "v  2 

R  =  =  correlation  coefficient  between  mid-parent 

v  i 


*  For  derivation  of  this  formula,  see  Appendix. 

t  The  offspring  will,  of  course,  form  an  array,  and  the  h$  is  the  deviation  of  its 
mean  from  the  mean  of  offspring  in  general. 

J  This  last  expression  is  inverted  because  we  desire  to  use  S  in  the  denominator. 


532 


TRANSMISSION 


We  are  now  able  to  put  formula  ( i )  in  the  form  of  a  regression 
equation,  giving  the  value  hz  as  follows  : 

hz  =  R  ^  H,  (4) 

which  is  the  deviation  of  this  special  population  from  the  mean 
of  the  race.1 

This  form  of  expression  of  formula  (i)  has  the  advantage  of 
simplicity.  Instead  of  the  deviations  (h^  and.  7z2)  of  two  parents 
with  variabilities  crl  and  cr2,  we  now  have  the  deviation  (H)  of  a 
single  artificial  mid-parent  made  by  first  transmuting  female 
deviations  into  male  values  by  multiplying  by  the  ratio  of  male 
to  female  variabilities  for  the  character  in  question  and  then 
taking  the  mean  of  the  male  and  the  transmuted  female  values.2 
This  is  Pearson's  mid-parental  deviation  (H). 

S  is  the  portion  of  this  formula  which  involves  the  variability 
of  parents,  for  it  depends  upon  cr1  and  upon  the  coefficient  of 
assortative  mating  (r3),  and  when  associated  with  H  as  it  is  in 
the  formula  it  may  be  looked  upon  as  expressing  the  variability 
of  the  mid-parent. 

Likewise  R  is  the  portion  of  the  formula  which  involves  the 
correlation  between  parent  and  offspring,  and  from  the  form  of 
equation  (4)  it  may  be  looked  upon  as  the  coefficient  of  correla- 
tion between  offspring  and  mid-parent. 

If  we  neglect  the  coefficient  of  assortative  mating,  making 
r%  =  o,  the  following  conclusions  may  be  drawn  from  formulas 
(3)  and  (4),  and  the  values  of  R  and  S: 

i.  The  variability  of  the  mid-parent  (S)  is  equal  to  that  of 
fathers  divided  by  V2.* 

1  Experimental  determinations  show  that  for  most  characters  thus  far  investi- 
gated the   regression  coefficient   of  offspring  as  compared  with   mid-parents   is 
about  0.6,  so  that  we  may  write,  in  general,  h%  —  0.6  H ;  or,  in  other  words,  if  a 
mid-parent  deviates  a  certain  amount  the  offspring  may  be  expected  in  general 
to  deviate  0.6  of  that  amount  from  the  mean  of  the  race. 

2  This  is  the  -  ( h±  +  —  h% }  —  Hoi  the  formula. 

2  \          cr2      / 

*  That  is,  in  S  =  — —      ^8  ,  if  assortative  mating  be  disregarded,  r&  becomes 

"V/2  f 

zero  and  the  formula  becomes  *l   _    ;  but  Vi  =  i,  and  we  have  -~< 

V2  V2 


HEREDITY 


533 


2.  The  correlation  of  sons  with  respect  to  mid-parents  (1?)  is 
equal  to  that  of  sons  with  respect  to  fathers  multiplied  by  V^.* 

We  have  answered  the  question  as  to  the  value  of  hz.  It 
remains  to  answer  the  question  as  to  the  value  of  2,  the  vari- 
ability (standard  deviation)  of  the  array  of  offspring  from  the 
particular  parents  of  deviations  h-^  and  h^.  If  we  assume  as 
before  that  ^  =  r2,  then  


The  fuller  treatment  of  the  meaning  of  this  formula  will  be 
taken  up  in  a  succeeding  section  on  "  Selection." 

We  could  now  proceed  to  form  a  mid-grandparent  in  the  same 
way  by  transmuting  female  values  into  their  male  equivalents 
by  multiplying  by  the  ratio  of  male  to  female  standard  devia- 
tions. Having  four  grandparents,  we  take  the  mean  of  the  four 
values  thus  obtained  for  our  mid-grandparent.  Similarly  this 
could  be  carried  back  to  any  number  of  generations,  and  we 
should  thus  derive  a  mid-parent  for  the  first,  second,  third,  etc., 
generations  of  ancestry.  These  can  be  conveniently  referred  to 
as  the  first,  second,  third,  etc.,  mid-parents  of  an  offspring. 

Formula  for  ancestral  heredity.  In  terms  of  these  mid-parents 
and  their  variabilities  Pearson  has  stated,  in  modified  and 
generalized  form,  Galton's  law  of  ancestral  heredity  as  follows  : 

/,      IO"7v_i_IO"w_LIO"*7_i  1<r£/ 

h  =  --  //i  H  ---  //a  +  T:  ~~  -"a  4-  ----  h  —  —  H  n  -r  •  •  -  , 
2  <TI  4  <r2  00-3  !1.~  <r,t 

in  which  h  is  the  deviation  from  the  mean  of  offspring  in  general 
to  be  expected  in  offspring  of  mid-parents  of  successive  genera- 
tions backward  whose  deviations  were  H^  H^,  H^  •••,  Hn\  cr  is 
the  standard  deviation  of  offspring  in  general  [the  cr3  of  formulas 
(i)  to  (4)  ]  ;  and  <rlt  <r2,  cr3,  .  .  .,  crw,  etc.,  are  the  standard  deviations 
of  the  mid-parents  of  successive  generations  of  ancestry. 

It  may  be  noted  from  this  formula  that  if  we  take  no 
account  of  differences  of  variability  in  successive  generations 
(<r  =  al  —  <r2  =  ...),  and  make  the  deviations  of  successive  mid- 
parents  equal  (ff^—  H^  =  H^  =  •  •  •},  we  obtain  Galton's  series, 

* 


*  That  is,  in  K  =  —  —  —  ,  if  ra  be  disregarded,  the  formula  becomes 


VI 


534  TRANSMISSION 

J-,  J,  J,  -^g-  •  •  •,  by  which  he  accounts  for  the  total  heritage.  This 
fractional  influence  of  the  different  generations,  therefore,  may 
be  accepted  as  the  best  general  statement  possible  of  the  law 
of  ancestral  heredity.  The  influence  of  individual  ancestors, 
waiving  all  considerations  of  special  prepotency,  would  be  found 
by  dividing  these  fractions  by  the  number  of  ancestors  of  that 
generation  (J  by  8  =  g1^  for  great-grandparents).  (See  table, 
page  527,  for  an  extended  statement  of  the  fractional  influence 
of  generations  and  separate  ancestors.) 

The  variability  of  the  offspring  of  an  ancestry  selected  for  an 
indefinitely  large  number  of  generations  back  is  given  by  a 
formula  which  is  merely  an  extension  of  the  formula  for  the 
variability  of  the  offspring  of  two  selected  parents.  If  we 
assume  Galton's  coefficients  in  the  law  of  ancestral  heredity, 
the  formula  for  the  general  case  may  be  written  as  follows  : 


2  V2          (2  V2)2          (2  V2)3  (2 

in  which  rlt  r2,  r3,  -  -,  rnt  are  the  coefficients  of  correlation 
between  offspring  and  the  first,  second,  third,  .  .  .,  nth  mid- 
parents.  Use  will  be  made  of  this  formula  in  treating  of  the 
reduction  of  variability  by  selection. 

SECTION  XV—  LIMIT  TO  THE  REDUCTION  OF 
VARIABILITY 

We  often  speak  of  "  fixing  "  the  type  by  selection,  meaning 
by  that  the  reduction  of  variability.  All  recent  studies,  however, 
go  to  show  that  we  do  not  greatly  reduce  variability  by  selection, 
however  much  we  alter  the  type. 

In  the  records  of  corn  breeding  it  will  be  remembered  that, 
while  the  protein  and  oil  contents  rapidly  responded  to  selection, 
yet  the  coefficients  of  variability  changed  but  little  ;  2  indeed,  it 
is  the  experience  everywhere  that  variability  is  but  slightly 
reduced  by  selection. 

This  experience  accords  with  mathematical  theory.  It  will 
be  shown  in  the  Appendix  that,  in  general,  the  variability  of  an 
array  is  obtained  from  the  standard  deviation  of  offspring  in 

1  See  Pearson,  Grammar  of  Science,  p.  482.  2  See  table,  p.  ^6. 


HEREDITY 


535 


general  by  multiplying  this  standard  deviation  by  Vi  —  r^  ;  that 
is,  in  symbolic  language,  ^  =  <73  Vi  —  rf  gives  the  variability 
(standard  deviation)  of  an  array  of  offspring  whose  correlation 
with  the  selected  parent  is  rlt  and  in  which  the  variability  of 
offspring  in  general  is  <r3. 

The  numerical  value  of  this  variability  in  a  given  instance 
depends  upon  the  value  of  r^  Now  experimental  evidence 
shows  that  the  correlation  between  parent  and  offspring  ranges 
all  the  way  from  0.3,  with  little  or  no  assortative  mating,  up  to 
about  o.  5  ,  with  the  highest  selection  of  both  parents  that  has  yet 
been  achieved  (see  table  of  coefficients  of  heredity,  page  488). 

Now  in  our  formula  ^  =  cr3  Vi  —  rf  let  us  substitute  these 
values  :  _ 

When  i\  =  0.3,  V  =  <73  Vi  —0.09  =  0.9539  °"3  ;  that  is,  in  this 
case,  when  one  parent  is  selected  we  get  an  offspring  only  about 
5  per  cent  less  variable  than  the  offspring  in  general. 

We  have  already  seen  (page  533)  that  when  two  parents  are  se- 
lected, assuming  them  to  be  equipotent,  the  formula  for  the  vari- 

I          2  r2 

ability  of  the  offspring  of  selected  parents  is  jv  =  o-3\  i  --  1-  . 

1  4-  *s 

Let  us  now  make  the  same  assumption  as  before  ;  namely,  take 
r±  first  as  0.3  for  pangamic  mating,  and  again  as  0.5  for  the  case 
of  perfect  assortative  mating. 


/ 

\l 


1.  If  rl  =  0.3  and  r%  =  b,  then  V  =  <73  \  I  --  ^-    becomes 

—  ~~  " 

i  --      -  =  <r3  Vo.82  =0.9055  a-3,  which  means  that  the 

selection  of  both  parents  out  of  a  race  developed  by  pangamic 
mating  will  result  in  the  reduction  of  variability  by  only  about 
10  per  cent. 

2.  If  T-J  =  0.5  and  rB  =  i,  —  that  is,  with  perfect  assortative 
mating  and  with  the  highest  correlation  found  in  highly  bred 
races,  - 


becomes 


—0.25  =0.8662  <J3; 


536  TRANSMISSION 

all  of  which  means  that  the  closest  selection  of  both  parents 
(perfect  assortative  mating)  cannot  result  in  the  reduction  of 
variability  by  more  than  about  13  per  cent. 

Moreover,  if  the  entire  back  ancestry  be  selected,  the  vari- 
ability will  not  be  much  reduced  below  this  point.  In  connec- 
tion with  the  law  of  ancestral  heredity  (page  534)  we  gave  a 
formula  for  the  variability  of  the  offspring  of  an  ancestral  line 
selected  back  for  an  indefinitely  large  number  of  generations. 
This  formula  is 

,\ 


2V2         ( 

in  which  2  is  the  variability  of  the  offspring  of  this  selected 
ancestry,  a-  is  the  variability  of  offspring  in  general  for  the 
population  from  which  selection  is  made,  and  r^  r2,  r^  ••-,  rn  are 
the  correlation  coefficients  of  offspring  and  first,  second,  third, 
.  .  .  ,  nth  mid-parents. 

For  pangamic  mating,  rlt  r2,  rs,  •  •  -,  rn  may  be  taken  as 
0.6       0.6         0.6  0.6 


Vz    (V2)2    (V^)3         '  (VI) 
Substituting  these  values  in  (i),  we  get 


2  .  .  0.6  0.6 


f         0.6  0.6 

22    22VI2 


=  0.8  cr2. 

=  <r  Vo.8  =  0.8944  <r, 

which  means  that  in  the  case  of  pangamic  mating  the  variability 
is  reduced  only  about  1  1  per  cent  by  selecting  the  entire 
ancestry. 

Basing  his  remarks  on  these   facts,  Pearson   says   that  the 
10  to   13  per  cent  reduction  obtained  by  the  selection  of  two 

*  The  series  -  -f  —2  -\  —  -  +  •  •  •  to  infinity  is  a  geometrical  progression  whose 
sum  is  found  in  the  usual  manner  by  dividing  the  first  term  by  i  minus  the  ratio. 


HEREDITY  537 

parents  is  "  almost  the  limit  of  the  reduction  of  variability,  even 
if  the  whole  back  ancestry  be  selected."  He  remarks,  of  course, 
that  the  new  variability  is  from  the  new  type,  not  the  unselected 
type ;  but,  he  adds,  "  continuous  selection  does  not  indefinitely 
modify  variability r,  however  much  it  shifts  the  type."  * 

The  principal  function  of  selection,  therefore,  is  to  alter  the 
type,  not  to  reduce  variability,  and  the  facts  here  cited  show 
the  inherent  impossibility  of  "  fixing"  the  type  in  the  sense 
that  individuals  will  not  depart  much  from  it.  But,  on  the 
other  hand,  the  same  principle  assures  us  that,  however  much 
we  improve  by  shifting  the  type,  there  always  remains  sufficient 
variability  for  still  further  selection,  and  as  long  as  variability 
remains  there  is  hope  and  possibility  for  still  further  improve- 
ment. We  may  therefore  fix  the  type  by  unchanging  standards 
of  selection,  in  the  sense  that  it  will  remain  stationary  and  not 
shift,  but  we  cannot  "  fix  "  it  in  the  sense  of  reducing  to  any 
great  extent  the  proportion  of  individuals  that  will  deviate 
from  it.2 

SECTION  XVI  — POWER  OF  SELECTION  TO  PERMA- 
NENTLY MODIFY  TYPES  BY  THE  ESTABLISH- 
MENT OF  BREEDS 

Though  selection  cannot  greatly  reduce  variability,  it  is  yet 
immensely  powerful  in  shifting  the  type,  as  has  been  shown, 
and,  if  long  continued,  in  so  establishing  the  new  type  that  it 
will  breed  true  thereafter  without  selection,3  as  will  now  be 
shown. 

This  will  necessitate  a  variety  of  assumptions  as  to  the 
ancestry  back  of  the  parent,  according  as  our  knowledge  of  its 
character  is  much  or  little,  and  according  as  it  may  be  assumed 

1  Pearson,  Grammar  of  Science,  pp.  458,  472-485.    (Italics  are  mine.) 

2  Ibid.  pp.  481-485. 

3  "  Without  selection"  here  means  absolute  freedom  from  the  influence  of  all 
laws  but  those  of  chance.    In  practice  we  never  realize  these  conditions,  so  that 
it  is  always  necessary  to  use  enough  systematic  selection  to  offset  the  effects  of 
that  degree  of  natural  selection  which  is  found  to  be  always  at  work  in  nature 
everywhere.    What  is  meant  is,  that   by  continued  selection  we  soon  reach  a 
point  at  which  the  inherent  variability  of  the  race  is  powerless  of  itself  to  alter 
the  type. 


538  TRANSMISSION 

to   be  mediocre    on    the    one    hand    or  something    more   than 
mediocre  on  the  other. 

Assuming  mediocrity  beyond  some  definite  point  in  the  back 
ancestry.  Galton's  form  of  the  law  of  ancestral  heredity  may 
be  written 


to  infinity,  in  which  h  has  the  meaning  denned  on  page  533. 

If  the  variabilities  of  successive  generations  be  taken  as 
equal,  the  fuller  statement  of  this  law  as  given  on  page  533 
reduces  at  once  to  this  simple  form. 

As  the  simpler  form  of  statement  gives  a  good  approximate 
value,  we  shall,  for  the  sake  of  simplicity  and  elegance  of  results, 
be  content  here  to  investigate  what  grows  out  of  this  law  in  the 
way  of  establishing  a  character  for  which  selection  and  breeding 
are  being  carried  on. 

i.  If  we  assume  mediocrity  back  of  the  immediate  parents, 
we  must  make 


Then  h  =  0.5  H±  ; 

that  is,  one  half  the  desired  character  is  present  in  the  offspring. 
2.   If  we  assume  mediocrity  back  of  the  grandparents,  we 
must  make 


Then  h  =  0.5  H^  +  0.25  H*. 

If  we  have  a  fixed  standard  of  selection,  H^  =  H^  ,  and 
^  =  0.75^. 

3.   If  we  assume  mediocrity  back  of  the  great-grandparents, 
we  must  make 

H,  =  HI  =  o. 

Then  h  =  0.5  H^  +  0.25  H^  -f-  o.i  25  Hz  ; 

and  with  a  fixed  standard  of  selection 

H\  =  J-J%  =  HZ  ; 
from  which  h  —  0.875  H^ 


HEREDITY  539 

If  this  same  line  of  argument  be  carried  on,  so  that  the  fourth 
generation  of  back  ancestry  is  selected, 

h  =  o-9375  -#!• 
Likewise,  if  the  fifth  generation  be  selected, 

h  =  0.9687^. 
And  if  a  sixth  generation  be  selected, 

h  =  0.9844  HI. 

The  significant  point  in  all  this  is  that  six  generations  of 
selection,  even  on  a  mediocre  stock,  establish  the  selected 
character  to  within  about  1.5  per  cent.  The  full  significance  of 
this  point  will  appear  later. 

Finally,  if  selection  of  the  character  of  deviation  H^  be  made 
for  n  generations,  and  if  we  may  assume  mediocrity  in  the 
ancestry  beyond  the  #th  generation,  the  amount  of  the  charac- 
ter established  is  given  by 


Making  no  assumptions  as  to  mediocrity  in  back  ancestry. 

It  has  been  shown  both  by  experimental  and  by  theoretical 
methods  that  if  mid-parents  with  character  H^  are  selected,  the 
offspring  will,  on  the  average,  exhibit  about  0.6  H^  of  the 
character  in  question.  The  inquiring  reader  will  ask  here  why 
this  differs  from  the  0.5^  obtained  from  Galton's  law.  It 
should  be  remembered  that  0.5^  is  what  we  obtained  by 
assuming  mediocrity  back  of  the  first  mid-parents.  In  general, 
if  we  select  parents  of  character  Hv  their  special  ancestry  will 
exhibit  this  character  to  a  greater  degree  than  ancestry  in 
general  from  which  the  selection  is  made.  It  is  therefore  only 
common  sense  to  expect  a  higher  value  than  0.5  ffl  under  the 
present  assumption. 

Granting,   then,   if   we   can   make   no   assertion  about   back 
ancestry,  that  an  offspring  will  exhibit  0.6  of  the  deviation  of 

*  1  1  --  I  is  the  sum  of  the  geometrical  progression  |  —  |  ---  1  ---  \~  '  '  '  ~^~ 
t  See  p.  533;  also  Proceedings  of  the  Royal  Society,  LXII,  396. 


540  TRANSMISSION 

selected  mid-parents,  Pearson  has  established,1  by  the  theory  of 
multiple  correlation,  the  following  results  : 

1.  If  selection  be  made  of  first  and  second  generations  of 
ancestry,  with  no  knowledge  as  to  back  ancestry, 

h  =  0.5122  HI  4-  0.2927  Hz. 

If  we  have  a  fixed  standard  of  selection,  H±  =  H2 ; 
then  h  =  0.8049  H±. 

2.  If    selection  be   made   of   three   generations   of   ancestry 
under  similar  conditions  as  to  back  ancestry, 

h  =  0.5015  H±  4-  0.2553  Hz  +  0.1459  ^s ; 
with  a  fixed  standard  Hlt 

h  =  0.9027  HI. 

3.  If  selection  be  made  of  four  generations  of  ancestry, 

h  —  0.5002  HI  4-  0-2507  H2  4-  0.1276^7.5  +  0.0729^/4; 
with  a  fixed  standard  H^ 

h  =  0.95147/1. 

4.  Similarly,  for  a  selection  of  five  generations, 

h  =  0.5000^4-0.2501  772  + 0.1253  ^4-0.0638^4  4-0.0365  HS\ 
and  with  a  fixed  standard  H^ 
/&  =  0.9717^. 

5.  Finally,  for  a  selection  of  six  generations, 

h  =  0.5000 .//!  4-0.2500^2  4-  0.1250^3  +  0.0627  HI 
4-0.0319^5  4-  0.0182  HS  ; 

and  with  our  fixed  standard  Hly 
h  =  0.9878  .#!. 

It  should  be  noted  that  the  coefficients  which  we  obtain  are 
approaching  more  and  more  Galton's  coefficients  in  the  law  of 
ancestral  hereditv,  which  means  that  if  selection  be  carried 
on  for  a  very  large  number  of  generations  it  does  not  matter 
whether  the  back  ancestry  of  our  selection  be  mediocre  or 
above  mediocrity. 

1  Proceedings  of  the  Royal  Societv,  LXII,  pp.  397-398. 


HEREDITY 


541 


SECTION  XVII  —  BREEDING  TRUE,  OR  STABILITY  OF  A 
CHARACTER  ESTABLISHED  BY  SELECTION 

It  is  the  object  of  this  section  to  show  that  if  an  improvement 
has  been  made  in  a  population,  or  if  a  breed  has  been  developed 
by  selection,  the  offspring  will  not  degenerate  if  allowed  to 
breed  among  themselves  without  selection  ;  that  is  to  say,  if  by 
selection  a  certain  per  cent  of  a  character  has  been  established 
on  the  average,  the  offspring  will  breed  true  to  that  amount  of 
the  character  which  has  been  established. 

For  instance,  if  selection  has  been  made  for  six  generations 
of  a  character  H^  the  amount  of  this  character  appearing  in  the 
offspring,  after  this  selection,  is  given  by  ||  Hv  if  we  assume 
mediocrity  back  of  the  six  generations  of  selected  ancestry. 
Now  if  these  offspring  with  ||  of  the  desired  character  be 
allowed  to  breed  together  without  further  selection,  their  off- 
spring will  exhibit  the  character  H^  in  the  amount  given  by 


/,^,*/,  IT  r/ 

i  +  ~  H\  +  Q  -H  i  H  -----  \-  —  H^  =  —  Hl\ 
2  \04/  48  2'  64 

so  that  the  first  generation  of  offspring  after  selection  has 
ceased  will  exhibit  the  character  to  exactly  the  extent  that  their 
parents  exhibited  it. 

Let  us    carry   this    forward  another   generation.     Then  the 
character  will  be  exhibited  in  the  amount  given  by 


4_  77     ,          77     .          J7     ,  //  77 

+  4^]     1  +  ^     1  +  ^~4     1  +  '   •  +  2^1  =  6^1' 

which  again  shows  the  offspring  unchanged  so  far  as  the  amount 
of  the  character  is  concerned  ;  and  it  is  easily  seen  that  this 
would  be  true  if  we  should  allow  breeding  to  go  on  for  any 
number  of  generations  without  further  selection  as  to  the  char- 
acter in  question.1 

For  the  sake  of  completeness  and  generality  let  us  consider 
the  case  where  selection  for  a  deviation  H^  has  been  made  for 
n  generations,  and  where  the  offspring  so  produced  are  allowed 

1  It  is  of  course  assumed  that  all  forms  of  natural  selection  are  also  excluded. 


542  TRANSMISSION 

to  mate  without  selection.  In  this  treatment  we  shall  assume 
mediocrity  in  this  back  ancestry  of  the  n  selected  generations 
of  ancestry. 

As  was  seen  on  page  539,  the  character  is  established  in  the 

amount  given  by  1 1 )  H\ ,  and  we  shall  now  show  that  if 

this  offspring  be  allowed  to  breed  without  further  selection  it 
will  breed  true  to  I of  the  selected  character. 

2" 

In   the   first  generation  of   offspring  after  no   selection   we 
should  have 


of  the  character  H^  in  question. 
This  series  may  be  written  as 


i/        i\      i/i       i 

-  i  -—+-(-  +  - 

2\  2"  /         2\2          22 


i        i  i         i  i  i 

—  ,  =~  h  —  ~+~  *  ~~  =i  —~ 

2"  2  2"  2  2n  2" 


The  amount  of  the  character  present  is  therefore  unchanged. 
In  the  second  generation  of  offspring  after  no  selection  we 
should  have 


so  that  the  amount  of  the  character  present  is  again  unchanged. 

The  method  here  used  can  be  extended  to  any  number  of 

generations.    We  may  show  that  if  it  be  true  for  the  rth  genera- 

tion of  offspring  bred  without  selection,  it  will  be  true  for  the 

(r+  i)th  generation.    If  i  --  -  of  the  character  has  appeared  in 

r  generations,  then  in  the  next  generation  the  amount  of  the 
character  should  be  given  by 


HEREDITY  543 


~ 


. 

which  shows  that  i of  the  desired  character  will  be  present 

2" 

in  any  generation.    Hence  the  stock  will  always  breed  true  to 
the  per  cent  of  the  character  established. 

It  may  be  remembered  in  the  above  that  mediocrity  has  been 
assumed  in  the  ancestry  back  of  the  n  selected  generations  of 
offspring ;  but  if  this  were  not  assumed,  we  have  seen  that  after 
a  few  generations  we  obtain  approximately  Galton's  coefficients. 
Hence,  without  assuming  mediocrity  back  of  n  generations,  we 
may  safely  say  that  the  offspring  will  breed  true  to  the  amount 
of  the  character  established  by  selection. 

The  following  table  presents  the  amount  of  a  character  estab- 
lished by  selection  of  i,  2,  3,  4,  5,  and  6  generations  of  ancestry. 
To  illustrate  how  these  breed  true  we  may  take  the  simplest 
case  where  0.6  of  the  character  is  established  by  selecting  one 
generation.  Suppose,  then,  that  a  generation  is  produced  with- 
out selection.  The  amount  of  the  character  present  will  be 
given  by 

(0.6)  (0.5 122)  +  0.2927  =  0.6, 

which  illustrates  that  stability  is  established. 


544  TRANSMISSION 

EFFECT  OF  CONTINUED  SELECTION  UPON  VARIABILITY  AND  TYPE  l 


NUMBER  OF 
GENERA- 
TIONS OF 
SELECTION 

FRACTIONAL  CONTRIBUTION  OF  ANCESTORS, 
VARIOUS  GENERATIONS 

RATIO  OF 
FINAL  TO 
SELECTED 
TYPE 

RATIO  OF 
FINAL  TO 
INITIAL 
VARIABILITY 

i 

a 

3 

4 

5 

6 

I 

2 

3 
4 
5 
6 

.6000 
.5122 

•Sols 

.5002 
.5000 
.5000 

.6000 

.8049 
.9027 

•95*4 
.9717 
.9878 

•9055 
.8946 

.8945 
.89445 

.8944 
.8944 

.2927 

•2553 
.2507 
.2561 
.2500 

•1459 
.1276 
•1253 
.1250 

.0729 
.0638 
.0627 

•0365 
.0319 

.0182 

To  infinity 

.5000 

.2500 

.1250 

.0625 

•03125 

.015625 

i 

.8944 

SECTION   XVIII  —  DURATION  OF  VARIETIES,  BREEDS, 
AND   FAMILY  STRAINS 

How  long  can  a  desired  breed  or  family  be  retained?  There  is 
a  popular  belief  that  varieties  wear  out,  and  that  breeds  must 
of  necessity  be  constantly  reenforced  by  new  material  or  by  new 
combinations  to  take  the  place  of  worn-out  stock. 

The  facts  just  presented,  however,  clearly  indicate  that  if  a 
type  does  not  remain  true  indefinitely  either  it  is  the  fault  of 
adverse  selection,  accidental  or  otherwise,  or  else  it  is  due  to 
some  physical  or  biological  cause,  for  the  type,  once  obtained, 
naturally  breeds  true. 

Again,  from  the  fact  that  variability  is  not  greatly  reducible, 
we  are  safe  in  assuming  that  types  once  established  by  selection 
will  not  only  remain  true  but  are  capable  of  still  further  develop- 
ment if  we  bestow  additional  attention  and  selection,  and  that 
the  upper  limits  of  improvement  are  fixed,  if  fixed  at  all,  by 
some  circumstance  other  than  variability.  It  may  be  biological, 
—  like  loss  of  fertility  or  reversal  of  selection,  —  or  it  may  be 
mechanical,  but  the  cause,  whatever  it  may  be,  that  sets  a  limit 
to  improvement  is  not  connected  with  variability. 

In  the  last  analysis,  however,  we  are  bound  to  raise  the  ques- 
tion whether  all  types  can  be  indefinitely  maintained,  even  by  the 

1  Pearson,  Grammar  of  Science,  p.  485. 


HEREDITY  545 

most  skillful  methods.  So  far  as  ordinary  laws  of  evolution  go 
there  is  no  doubt  about  it,  and  we  can  with  confidence  assert 
our  ability  to  maintain  a  desirable  type  indefinitely ;  but  are 
there  biological  considerations  outside  of  mere  variability  that 
tend  to  extinction  ?  Do  species  "  wear  out,"  or  do  they  come  to 
an  untimely  end  by  accident  only  ? 

In  the  opinion  of  the  writer  we  do  not  possess  sufficient  reli- 
able data  on  this  point  to  warrant  confident  assertion.  It  is 
probably  true  that  species  have  disappeared  off  the  earth  at  a 
rate  not  equaled  by  the  production  of  new  species.  It  is  true, 
too,  that  among  domestic  animals  some  of  the  most  valuable 
lines  have  disappeared  in  spite  of  the  most  energetic  efforts  to 
preserve  them.1  In  the  instance  given  below  the  extinction  is  to 
be  definitely  ascribed  to  barrenness,  —  a  defect  perfectly  well 
known  to  breeders,  and  considered  by  them  at  the  time  as  fortu- 
nate, in  the  interest  of  high  prices,  they  evidently  not  appreciating 
the  inevitably  fatal  consequences  of  racial  barrenness. 

On  the  other  hand,  many  species  have  persisted  from  remote 
times  practically  unchanged  in  type  (oaks  and  tulip  trees),  and 
as  we  are  fully  informed  as  to  some  of  the  causes  that  resulted 
in  the  extinction  of  favorites,  like  the  unfortunate  family  of  Short- 
horns just  'mentioned,  we  are  warranted  in  hoping  that  species 
in  general  may  be  maintained  indefinitely. 

The  conclusion  is  forced  upon  us  that  reliable  information  is 
wanting  as  to  whether  all  types  can  be  indefinitely  maintained. 
No  proper  attempt  was  made  to  save  the  Duchess  family.  Its 
inherent  weakness  was  counted  its  chief  virtue,  and  there  could 
be  but  one  conclusion.  But  was  its  fertility  a  waning  character, 
which  no  amount  of  selection  could  have  strengthened  ?  Again 
we  say  that  our  knowledge  is  insufficient  for  the  answer. 

Summary.  Heredity  is  not  the  relation  between  the  offspring 
and  his  parent  simply,  but  the  relation  between  him  and  the 
whole  back  ancestry.  The  characters  of  the  individual  are  the 
characters  of  the  race.  Some  are  well  developed,  others  are 
undeveloped  or  latent,  but  all  are  there  in  some  degree. 

1  For  example,  the  Duke  and  Duchess  Shorthorns,  the  most  famous  family  of 
any  breed, — so  famous  that  a  heifer  brought  $40,600  at  the  New  York  Mills  sale 
in  1873. 


546  TRANSMISSION 

Different  individuals  of  the  same  ancestry  inherit  differently, 
and  in  general  the  behavior  of  characters  in  transmission  sug- 
gests that  they  are  in  some  way  made  up  of  combinations,  so 
that  a  high  degree  of  variability  is  inevitable,  even  with  the 
same  elements  ;  as,  for  instance,  a  great  variety  of  color  effects 
can  be  produced  with  the  same  three  primaries,  —  red,  blue,  and 
yellow. 

Some  characters  blend  and  others  are  mutually  exclusive, 
each  tending  to  preserve  its  identity.  On  this  account,  as  well 
as*  from  other  causes,  such  as  relative  fertility,  races  often 
exhibit  distinct  polymorphism.  Inheritance  is  not  so  much  con- 
nected with  sex  as  is  popularly  supposed.  Characters  often 
do  not  develop  until  late  in  life.  This  is  not  to  be  regarded  as 
belated  inheritance  but  as  belated  development. 

The  only  proper  way  to  study  the  principles  of  heredity  is  by 
statistical  methods,  using  groups  instead  of  single  individuals, 
from  which  no  general  conclusions  can  be  safely  drawn. 

The  regression  table  brings  out  clearly  the  fact  that  like 
parents  beget  unlike  offspring ;  that,  in  general,  the  offspring 
is  more  mediocre  than  the  parent,  but  that  for  selected  offspring 
the  ancestry  is  comparatively  mediocre ;  that  the  coefficient  of 
heredity  between  the  nearest  relatives  is  seldom  above  0.50; 
that  the  mean  of  the  offspring  is  not  necessarily  the  same  as  the 
mean  of  the  parent ;  that  the  means  of  a  race  are  its  most  fertile 
portions ;  that,  in  general,  a  few  offspring  exceed  the  previous 
limits  of  the  race,  —  that  is,  progress  away  from  the  type  if 
favored  by  selection ;  that  exceptional  individuals  may  arise 
either  from  exceptional  or  from  mediocre  parentage ;  and  that 
successive  offspring  from  the  same  parents  are  not  identical. 

Nothing  is  clearer  than  that  the  inevitable  consequences  of 
bisexual  reproduction  and  of  the  manner  of  growth  by  the  halv- 
ing of  the  cell  contents  is  to  insure  that  character  combinations 
effected  in  this  manner  are  brought  together  in  definite  mathe- 
matical proportions  not  far  from  those  expressed  jn  the  expan- 
sion of  a  binomial.  This  is  the  real  foundation  of  Mendel's  law, 
for  characters  that  do  not  blend,  and  it  also  expresses  the  rela- 
tive proportions  of  characters  that  do  blend. 

The  statistical  methods  of  study  enable  us  to  develop  the  law 
of  ancestral  heredity,  which  agrees  closely  with  experimental 


HEREDITY  547 

evidence,  and  which  shows  the  degree  to  which  the  various  gen- 
erations have  contributed  to  the  results. 

Continued  selection  will  shift  the  type  in  any  desired  direction, 
and  after  a  few  generations  it  will  "  breed  true  "  in  its  new  form. 
As  variability  is  not  greatly  reduced  by  selection,  there  is  always 
opportunity  for  improvement  so  far  as  variability  is  concerned. 

SPECIAL  EXERCISES 

1 .  Exercises  in  great  variety  in  forming  regression  tables  and  in  deducing 
the  conclusions. 

2.  Investigations  into  the  operations  of  Mendel's  law,  by  the  examina- 
tion and  identification  of  laboratory  material  and  if  possible  by  the  actual 
raising  of  crossed  forms  for  the  purpose. 

3.  Special  and  definite  applications  of  the  law  of  ancestral  heredity 
to  the  problems  of  the  breeder,  especially  in  crossing,  grading,  and  line 
breeding. 

ADDITIONAL  REFERENCES 

ALTERNATIVE    INHERITANCE.    By    Karl    Pearson.    Proceedings   of   the 

Royal  Society,  LXXII,  505-510. 
AMERICAN   TROTTING    RECORDS   AS    DATA   FOR   HEREDITY   STUDIES. 

By    Francis    Galton.      Proceedings    of    the    Royal    Society,    LXII, 

310-315. 
BATESON  ON   PEARSON'S  CONCEPTION  OF  HEREDITY.    Proceedings  of 

the  Royal  Society,  LXIX,  193-205  ;  Pearson's  answer,  LXIX,  450. 
CHANCES  OF  DEATH.    By  Karl  Pearson.    Science,  VI,  328-330. 
CONTRIBUTION  OF  SEVERAL  ANCESTORS  TO   OFFSPRING.    By  Francis 

Galton.    Proceedings  of  the  Royal  Society,  LXI,  401-413. 
CORRELATION   BETWEEN   LONGEVITY  AND  FERTILITY.    By  Karl   Pear- 
son.   Proceedings  of  the  Royal  Society,  LXVII,  159-179*  333-337- 
CRITERION  TO  TEST  THEORIES  OF  HEREDITY.    By  Karl  Pearson  (1904). 

Proceedings  of  the  Royal  Society,  LXXII  I,  262-280. 
Do  VARIETIES  RUN  OUT?    By  J.Craig.    Gardening,  1899,  pp.  278-279  $ 

also  in  Experiment  Station  Record,  XI,  152. 
EXPERIMENTAL    EVIDENCE    UPON    MENDEL'S    LAW.      By  L.  H.  Lock. 

Nature,  LXX,  601-602;    by  Karl  Pearson,  626-627. 
EXPERIMENTAL    STUDIES   IN    HEREDITY.     Corn   Report   of  the    Royal 

Society,  1902,  p.  160  ;  also  in  Experiment  Station  Record,  XVII,  634. 
EXPERIMENTAL  ZOOLOGY.    By  T.  H.  Morgan.    Chapters  VI  and  VII, 

pp.  66-166. 
EXPERIMENTS  IN  CROSSING  WHITE  AND  BLACK  OATS.  By  J.  H.  Wilson. 

Nature,  1904,  p.  413  ;   Experiment  Station  Record,  XVI,  462. 


548  TRANSMISSION 

EYE  COLOR  IN  MAN.  Philosophical  Transactions  of  the  Royal  Society, 
CXCV,  A,  79-150. 

FORMULA  FOR  REGRESSION.  By  Pearson  and  Yule.  Proceedings  of  the 
Royal  Society,  LX,  477-489. 

HEREDITY  OF  COAT  CHARACTERS  IN  PIGS  AND  RABBITS.  By  W.  E. 
Castle.  Science,  XXI,  737-738,  986. 

HISTORY  OF  THE  DEVELOPMENT  OF  THE  QUANTITATIVE  STUDY  OF 
VARIATION.  By  C.  B.  Davenport.  Science,  VIII,  864;  Proceedings 
of  the  American  Association  for  the  Advancement  of  Science,  1900, 
XLIX,  197-200. 

HYBRID  ORANGES.  By  Webber  and  Swingle.  Science,  XVII,  262- 
263. 

HYBRID  WHEATS.  By  W.  J.  Spillman.  Bulletin  No.  115,  Office  of  Ex- 
periment Stations  ;  also  in  Science,  XX,  68. 

INHERITANCE  IN  COAT  COLOR,  THOROUGHBRED  HORSES.  By  Blan- 
chard.  Biometrika,  I,  361-364  ;  by  Karl  Pearson,  Philosophical 
Transactions  of  the  Royal  Society,  CXCV,  A,  1-49. 

INHERITANCE  OF  FERTILITY.  (Race  horses  and  the  human  race.)  By 
Karl  Pearson.  Science,  IX,  283-286. 

INHERITANCE  OF  MENTAL  CHARACTERS  IN  MAN.  By  Karl  Pearson. 
Proceedings  of  the  Royal  Society,  LXIX,  153-155. 

LATENT   CHARACTERS    AND   REVERSION.    By  W.  E.  Castle.    Science, 

XXI,  378-379- 
LAW  OF   ANCESTRAL   HEREDITY.    By   Karl    Pearson.    Biometrika,    II, 

211-229,  231-236. 

LAW  OF  HEREDITY.    By  C.  B.  Davenport.    Science,  VII,  158-161. 
LAW   OF    REVERSION.     By    Karl    Pearson.     Proceedings   of   the    Royal 

Society,  LXVI,  140-164,  241-244,  316-323,  324-327. 
LAWS    OF   ANCESTRAL   HEREDITY.    By    Karl   Pearson.     Science,   VII, 

337-339.  551-554- 

LAWS  OF  HEREDITY  OF  GALTON  AND  MENDEL,  AND  SOME  LAWS 
GOVERNING  IMPROVEMENT  BY  SELECTION.  By  W.  E.  Castle.  Pro- 
ceedings of  the  American  Academy  of  Arts  and  Sciences,  XXXIX, 
221-242. 

LIMITS  OF  VARIATION  IN  PLANTS.  (Author  says  variation  is  in  mathe- 
matical ratio.)  By  J.  W.  Harshberger.  Science,  XIII,  251. 

LONGEVITY  AND  THE  SELECTIVE  DEATH  RATE.  Pearson  and  Beeton. 
Proceedings  of  the  Royal  Society,  LXV,  290-305. 

MATHEMATICAL  CONTRIBUTION  TO  THE  THEORY  OF  HEREDITY.  By 
Karl  Pearson.  Proceedings  of  the  Royal  Society,  LXXI,  288-314. 

MATHEMATICAL  EVOLUTION.  By  Karl  Pearson.  Proceedings  of  the 
Royal  Society,  LIV,  329. 

MATHEMATICAL  EVOLUTION.  By  Karl  Pearson.  Proceedings  of  the 
Royal  Society,  LXIV:  Genetic  Selection,  163-165;  Inheritance  of 
Fertility,  165-166;  Inheritance  of  Fecundity,  166-167. 


HEREDITY  549 

MATHEMATICAL  EVOLUTION  AND   MENDEL'S   LAW.    By   Karl  Pearson 

(1904).    Philosophical  Transactions  of  the  Royal  Society,  CCIII,  A, 

53-86. 
MATHEMATICAL   EVOLUTION  —  CORRELATION.     By   Lee   and   Pearson. 

Proceedings  of  the  Royal  Society,   LXI,  343-356;  LXII,   173-175, 

386-417;  LXIII,  417-419. 
MATHEMATICAL   EVOLUTION  —  SOME    ERRORS   TO   BE    AVOIDED.     By 

Karl  Pearson.    Proceedings  of  the  Royal  Society,  LX,  489-498  ;  On 

Spurious  Correlation,  498-502. 
MEASURING   VARIATIONS    IN    ANIMALS.     (Report   of  a   committee   of 

Galton    and    others.)     Proceedings    of    the    Royal    Society,    LVII, 

360-382. 
MENDELIAN  INHERITANCE  OF  THREE  CHARACTERS.  By  William  Bateson. 

Proceedings  of  the  Cambridge  Philosophical  Society,  XII,  153-154. 
MENDELISM.     (Experiments   with   guinea-chicken    hybrids.)    By    M.   L. 

Snyder.    Science,  XXI,  854-855. 
MENDEL'S  LAW.    (Angora  goats.)    By  W.  E.  Castle.    Science,  XVIII, 

760-761. 
MENDEL'S    LAW.    By    A.   D.   Darbishire.    Experiment    Station    Record, 

XVI,  232. 
MENDEL'S  LAW  (Exceptions   to).     By  W.  J.  Spillman.     Science,  XVI, 

709-710,  794-796. 
MENDEL'S  LAW.    (Experiments  with  mice.)   By  C.  B.  Davenport.   Science, 

XIX,  110-114. 
MENDEL'S  LAW  AND  CYTOLOGICAL  INVESTIGATION.    By  C.  B.  Wilson, 

Science,  XVI,  991-993. 
MENDEL'S    LAW    AND    NEGRO    ALBINISM.     By    William    C.  Larrabee. 

Science,  XVII,  75-?6. 
MENDEL'S  LAW.    DEFENSE  BY  BATESON.    Cambridge  University  Press 

1902,  p.  212  ;  Experiment  Station  Record,  XIV,  634. 
MENDEL'S  LAW,  —  DISCUSSION,  DEFENSE,  AND  CRITICISM.    Biometrika, 

1902,  No.  2,  pp.  228-254  ;  Journal  of  the  Royal  Horticultural  Society, 

1902,  pp.  688-695  ;  Experiment  Station  Record,  XIV,  446-447. 
MENTAL  AND  MORAL  HEREDITY  IN  ROYALTY.    By  Dr.  F.  A.  Woods, 

Harvard  University.    Popular  Science  Monthly,  LXI,  three  articles ; 

LXII,  six  articles. 
NEW   EVIDENCE   FOR    INDIVIDUALITY   OF   CHROMOSOMES.    By  W.  J. 

Baumgartner.    Biological  Bulletin,  VIII,  1-23. 
Ox  THE  INFLUENCE  OF  SELECTION  IN  VARIABILITY.    By  Karl  Pearson. 

Proceedings  of  the  Royal  Society,  LXIX,  330-332. 

ORIGIN  OF  BLACK  SHEEP  IN  A  FLOCK  (Mendelian).     By  C.  B.  Daven- 
port.    Science,  XXII,  674-675. 

PURITY  OF  GERM  CELLS.    By  T.  H.  Morgan.    Science,  XXII,  877-879- 
REGRESSION    AND    INHERITANCE   IN    THE    CASE   OF    Two   PARENTS. 

Proceedings  of  the  Royal  Society,  LVIII,  240-242. 


550  TRANSMISSION 

REGRESSION,  HEREDITY,  PANMIXIA.    By  Karl  Pearson.    Proceedings  of 

the  Royal  Society,  LIX,  69-70. 
REPRODUCTIVE    SELECTION.     By    Karl   Pearson.     Proceedings    of    the 

Royal  Society,  LIX,  301-304. 
SECOND-GENERATION  HYBRIDS.    By  Halstead  and  Kelsey.    New  Jersey 

Experiment  Station  Report,  1902,  pp.  377-395  ;  Experiment  Station 

Record,  XV,  152. 
SKEW  VARIATION.    By  Karl  Pearson.    Proceedings  of  the  Royal  Society, 

LVII,  257-260. 
STATEMENT  OF  MENDEL'S  LAW.    (With  bibliography.)   By  W.  E.  Castle. 

Science,  XVIII,  396-405  ;  also  by  L.  H.  Bailey,  XVII,  441-454 
TELEGONY    IN    MAN.     By    Karl    Pearson.     Proceedings   of   the    Royal 

Society,  LX,  273-283. 
THE     STATISTICAL     STUDY    OF     EVOLUTION.     By    C.    B.    Davenport. 

Popular  Science  Monthly,  LIX,  447-460. 

VARIABILITY  OF  INDIVIDUAL  AND  RACE.    By  Karl  Pearson.    Proceed- 
ings of  the  Royal  Society,  LXVIII,  1-5,  372-373. 
VARIATION   AND   CORRELATION   IN    MAN  —  CIVILIZED  AS  COMPARED 

WITH  PRIMITIVE  RACES.    By  Karl  Pearson.    Science,  VI,  49-50. 
WONDER    HORSES    AND    MENDELISM.     (Several   generations   of  horses 
with  very  long  manes  and  tails.)    By  C.  B.  Davenport.    Science,  XIX, 


CHAPTER    XV 

PREPOTENCY 

That  all  parents  are  not  equally  powerful  in  impressing 
racial  characters  is  a  fact  well  known  to  the  merest  novice  in 
breeding.  It  is  distinctly  shown  in  all  regression  tables,  and 
the  reason  for  it  is  clearly  seen  in  the  mathematical  nature  of 
reproduction,  by  which  individuals  are  differently  endowed,  and 
by  which  some  few  are  exceptionally  rich  in  the  elements  out  of 
which  racial  characters  are  developed.  When  to  these  facts  is 
added  the  difficulty  of  selecting  animals  by  outward  appearance, 
on  account  of  the  relation  of  dominant  and  recessive  characters, 
we  need  feel  no  surprise  at  the  relatively  small  number  of 
highly  prepotent  individuals  and  the  large  number  of  reversions 
encountered  in  actual  breeding. 

SECTION  I  — DATA  FROM  THE  TROTTING  RECORDS 
ILLUSTRATING  PREPOTENCY 

Seeking  material  which  would  illustrate  accurately,  and  with 
sufficiently  large  numbers,  the  differences  in  the  breeding  powers 
of  different  individuals,  the  writer  made  some  studies  in  the 
records  of  trotting-bred  horses.  These  studies  covered  all 
animals  registered  and  that  had  made  track  or  breeding  records 
from  the  opening  of  the  Register  and  the  Yearbook  down  to 
and  including  the  year  igoi.1 

In  the  consideration  of  this  material,  and  in  the  comparison 
of  individuals,  four  facts  must  be  borne  in  mind  :  first,  some 
individuals  were  too  young  for  their  full  breeding  record  to  be 
all  in ;  second,  some  had  enjoyed  less  opportunity  than  others, 
owing  to  their  racing  engagements  ;  third,  some  stallions  had 
access  to  better  mares,  and  more  of  them,  than  had  others ; 

1  It  is  needless  to  say  that  this  proved  a  laborious  task,  covering  many  weeks*, 
with  two  calculators. 

551 


552 


TRANSMISSION 


fourth,  fashion  has  much  to  do,  even  among  race  horses,  in 
influencing  selection,  especially  after  an  individual  or  a  family 
has  acquired  a  reputation. 

Allowing  as  fully  as  possible  for  these  facts,  the  records  are 
worth  study  for  the  light  they  throw  upon  the  question  of 
inherent  differences  between  individuals  in  respect  to  breeding 
powers  —  differences  so  great  that  as  we  proceed  it  will  be 
perfectly  evident  that  the  line  of  descent  runs  through  few 
individuals  and  quite  independent  of  the  mass. 

The  total  number  of  performers  listed  —  that  is,  that  had 
made  track  records  good  enough  to  admit  them  to  the  2:30  list 
at  this  date  (1901) —  was  26,327,  of  which  17,625,  or  almost 
exactly  two  thirds,  were  trotters,  and  8702  were  pacers. 

The  Register  showed  that,  in  all,  34,299  stallions  had  been 
recorded  at  this  time,  but  the  breeding  record  showed  that  only 
6278,  or  less  than  one  in  five,  had  produced  anything  in  the  list; l 
that  is  to  say,  roughly  speaking,  6278  sires  had  produced  26,327 
performers,  or  an  average  of  4.  i  +  each. 

Great  sires.  Of  these  6278  sires  only  207  had  produced  ten 
or  more  sires  or  dams  of  speed;  that  is,  only  207  had  bred  well 
enough  to  produce  either  ten  stallions  each,  or  ten  mares  each, 
capable  themselves  of  producing  speed.2  In  other  words,  of  the 
whole  34,299  stallions  and  6278  sires,  only  207  bred  speed  well 
enough  to  send  it  into  the  second  generation  to  the  extent  of 
either  ten  sires  or  ten  dams  producing  speed. 

Now  these  207  great  sires  themselves  produced  directly  5377 
performers  (4226-1151  p.),3  which  is  more  tJian  one  fifth  of 
the  entire  list  of  performers,  and  an  average  of  26  apiece,  or 
six  times  the  breeding  record  of  the  average  stallion. 

Again,  these  207  great  sires  produced  3155  sires  of  performers, 
and  they  in  turn  produced  16,536  trotters  and  pacers  (11,737- 
4799  p.).  This  is  over  half  of  all  the  sires  and  over  62  per  cent 
of  all  the  performers  of  the  breed. 

1  This  was  partly,  as  has  been  already  noted,  because  some  individuals  were  too 
young  to  have  made  a  full  breeding  record. 

'*  This,  of  course,  does  not  include  those  sires  whose  produce  in  sires  and  dams 
together  equaled  ten. 

8  Note  that  4226—1151  p.  means  4226  trotters  and  1151  pacers. 


PREPOTENCY 


553 


Besides  this,  these  same  207  sires  produced  4507  dams  of 
speed,  and  they  produced  6691  performers  (5120—1571  p.);  so 
that  about  3  per  cent  of  the  sires  have  produced  the  sires 
and  dams  of  somewhere  between  two  thirds  and  three  quarters 
of  the  total  speed  of  the  race.  If  we  should  add  the  produce  of 
the  sires  and  the  dams,  we  should  have  16,536  -f  6691  =  23,227 
apparent  grandchildren  of  those  207  sires.  This  we  cannot  do 
because  many  of  those  recorded  as  offspring  of  dams  are  also 
recorded  among  the  offspring  of  sires ;  that  is  to  say,  they  are 
duplicates  due  to  the  fact  that  many  of  the  4507  dams  were  mated 
with  some  of  the  3155  sires.  We  cannot  tell,  therefore,  from 
these  figures  what  exact  proportion  of  the  total  number  registered 
may  have  descended  from  the  207  great  sires. 

Distinction  between  sires  of  sires  and  sires  of  dams.  Ana- 
lyzing these  207  great  sires,  it  was  found  that  they  were  un- 
equally divided  between  sires  of  sires  and  sires  of  dams  of  speed 
as  follows  : 

Class  i.  Sires  of  ten  or  more  sires  of  speed,  but  of  less  than 
ten  dams  of  speed,  —  9. 

Class  2.  Sires  of  ten  or  more  dams  of  speed,  but  of  less  than 
ten  sires  of  speed,  —  113. 

Class  3.  Sires  of  ten  or  more  sires  of  speed  and  of  ten  or 
more  dams  of  speed,  —  85. 

Of  these  three  classes,  i  may  be  considered  as  distinctly  sires  of 
sires,  2  as  sires  of  dams,  and  3  as  sires  of  both  sires  and  dams. 

From  the  table  on  the  following  page  it  appears  that : 

1.  The  poorest  breeding  record  was  made  in  every  case  but 
one  by  Class  2,  — the  sires  of  ten  or  more  dams  but  not  of  ten 
or  more  sires.    Note  the  ratios,  lines  3,  5,  7,  8,  10,  12,  13,  15. 
The  only  case  in  which  they  outdid  Class  i  was  in  the  ratio  of 
clams  produced  per  stallion  (15),  which  was  clearly  in  excess  of 
Class  i  (6),  which  are  distinctly  stallion  breeders  (line  10). 

2.  The  great  breeding  record  was  made  by  Class  3,  —  the 
sires  that  produced  both  sires  and  dams  freely.    In  every  case 
the  ratios  are  higher  than  for  any  other  class,  whether  performers, 
sires,  dams,  or  produce  of  sires  or  dams. 

3.  Class  i,  sires  of  sires,  was  clearly  superior  to  Class  2,  sires 
of  dams,  but  in  all  cases  inferior  to  Class  3,  sires  of  both. 


554 


TRANSMISSION 


BREEDING  RECORD  OF  THREE  CLASSES  OF  STALLIONS  :   i ,  SIRES  OF 

SIRES;  2,  SIRES  OF  DAMS;  3,  SIRES  OF  BOTH  SIRES 

AND  DAMS  OF  SPEED 


CLASS  i 

CLASS  2 

CLASS  3 

Number  of  sires  . 

I  T  -3 

8c 

2 

Total  performers  gotten  directly  by  these  sires  . 
Ratio  per  sire 

274 
-?o 

1  l  J 
1357 

12 

u  j 
3>746 

A  A 

4 
5 

; 

Sires  of  performers  gotten  by  each  class  .  .  . 
Ratio  per  original  sire  
Performers  gotten  by  these  sires  (line  4)  ... 
Ratio  per  sire  (line  4) 

"3 

12 

332 
->_L 

461 

4 
1396 

-}  + 

2,581 

3° 
14,808 

6- 

8 
9 

10 

ii 

I  2 

Ratio  to  original  sires  (line  i)  
Dams  of  performers  gotten  by  original  sires  .  .  . 
Ratio  to  original  sires  
Performers  produced  by  these  dams  (line  9)  .  . 

J~ 

37 
57 
6 
60 
i  + 

12  + 
1677 

15 
2342 
I.C  — 

i?4 

2,773 
32 
4,289 
!.<;  + 

Ratio  to  original  sires  (line  i) 

7  — 

2O  + 

CQ  + 

1  J 
H 
15 

Performers  (line  4)  that  were  also  sires  of  speed  . 
Ratio  to  original  sires  (line  i)  . 

40 

4  + 

J45 

i  + 

888 
10  + 

4.  One  outside  circumstance  helps  to  relieve  the  burden  of 
inferiority  resting  on  Class  2.    A  stallion  belonging  to  an  un- 
fashionable line  would  be  used  but  little  or  not  at  all  in  the  stud, 
while  a  mare  belonging  to  an  equally  unfashionable  strain  would 
not  be  equally  barred.    The  result  of  this  discrimination  in  the 
long  run,  and  under  our  methods  of  study,  would  appear  in  the 
form  of  sires  of  dams.    To  some  extent  it  means,  not  that  these 
sires  did  not  prodtice  males,  but  that,  being  unfashionable,  these 
males  had  little  opportunity.    This  probably  does  not  account 
for   all    differences,    even   though    the    turns    and    caprices   of 
fashion  are  harder  on  sires  than  on  dams. 

It  must  not  be  forgotten  in  this  connection  that  these  1 1 3  sires 
constitute  more  than  one  half  of  the  207  greatest  sires  of  the  race. 
They  could  not,  therefore,  have  been  so  very  unfashionable. 

5.  Class  i  must  be  largely  what  it  seems  to  be,  —  breeders 
of  sires  rather  than  of  dams,  because  there  is  no  reason  why  its 
female  offspring  should  have  been   suppressed.    It   is   clearly 
superior  to  Class  2,  but  inferior  to  Class  3. 


PREPOTENCY 


555 


6.  Class   3  evidently  represents   the   cream   of   the   race,  — 
exceedingly  prolific  and  highly  fashionable,  —  the  most  success- 
ful getters  both  of  speed  and  of  breeders. 

7.  These  85  sires  themselves  produced  directly  2581  sires  of 
performers  (30  apiece),  this  number  being  over  40  per  cent  of 
all  the  sires  of  the  breed.    They  produced  directly  3746  per- 
formers, or  14  per  cent  of  all  in  the  list.    The  2581  sires  directly 
gotten  by  them  produced  14,808  performers,  or  over  56  percent 
of  all  in  the  list.    This  means  that  a  little  over  one  per  cent  of  the 
sires  are  grandsires  to  over  half  tJie  breed. 

The  big  ten.  But  the  highest  relative  excellence  is  well  within 
these  85  great  breeders.  Their  average  get  of  performers  was 
44,  or  over  ten  times  the  average  of  the  race,  but  out  of  the 
34,299  registered  stallions  ten,  and  ten  only,  produced  directly 
as  many  as  a  hundred  or  more  performers  each.1  The  tabulation 
of  the  breeding  record  of  these  ten  greatest  stallions  is  good 
reading  for  the  student  of  prepotency,  as  it  shows  a  breeding 
power  which  fully  justified  their  fame  as  great  producers  not 
only  of  speed  but  of  sires  and  dams  of  speed. 


TABLE  SHOWING  THE  RECORD  OF  THE  TEN  GREATEST  PRODUCERS 

OF  SPEED2  UP  TO  AND  INCLUDING  IQOI 


SIRE 

SIRED  BY 

TROTTERS 

PACERS 

TOTAL 

I 

Nutwood  600       .     .     . 

Belmont  64    .     .     .    .* 

'31 

34 

I65 

2 

Electioneer  125  .     .     . 

Hambletonian  10    .     . 

I58 

2 

160 

3 

Onward  1411  .... 

Geo.  Wilkes  519     .     . 

124 

34 

158 

4 

Red  Wilkes  1749     .     . 

Geo.  Wilkes  519     .. 

116 

4i 

'57 

5 

Alcantara  729      ... 

Geo.  Wilkes  519     .    , 

102 

47 

149 

6 

Pilot  Medium  1579  .     . 

Happy  Medium  400    . 

94 

20 

114 

7 

Simmons  2744     .     .     . 

Geo.  Wilkes  519     .     . 

82 

23 

io5 

8 

Wilton  5982    .... 

Geo.  Wilkes  519     .     . 

89 

M 

103 

9 

Gambetta  Wilkes  4651 

Geo.  Wilkes  519     .     . 

49 

52 

101 

10 

Baron  Wilkes  4758  .     . 

Geo.  Wilkes  519     .     . 

78 

21 

99 

Total    .     . 

IO27 

288 

nn 

Average 

IO2 

2Q 

i7i 

1  One  of  these  goes  in  at  99. 


2  Trotters  and  pacers. 


556 


TRANSMISSION 


This  is  32  times  the  breeding  record  of  the  average  sire,  and 
nearly  five  times  the  record  of  the  207  great  sires,  themselves 
included,  or  over  six  times  their  record  exclusive  of  these  ten. 

It  is  worth  while  to  note  the  sires  of  these  great  breeders  of 
speed.  Number  2  is  by  Hambletonian  10;  No.  6  is  by  Happy 
Medium,  he  by  Hambletonian  10;  No.  I  is  by  Belmont,  by 
Abdallah,  he  by  Hambletonian  10;  and  the  remaining  seven, 
Nos.  3,  4,  5,  7,  8,  9,  10,  are  by  Geo.  Wilkes,  by  Hamble- 
tonian 10.  Thus,  of  this  remarkable  list  of  ten  stallions,  all 
except  one  are  but  two  removes  from  Hambletonian  10.  Of  this 
number,  those  that  were  sired  by  Geo.  Wilkes  produced  640 
trotters  and  232  pacers,  —  in  all  872  performers,  or  more  than 
66  per  cent  of  the  whole. 

The  famous  grandsires.  Eight  stallions  of  this  list  have  the 
distinction  of  being  grandsire  to  over  500  performers,  as  follows  : 


TABLE  OF  FAMOUS  GRANDSIRES  HAVING  500  OR  MORE  PERFORMERS 
IN  THE  SECOND  GENERATION  * 


I 

2 

3 

4 

5 

6 

7 

8 

Name 

Per- 
formers 

Sires 

Per- 
formers 

Dams 

Per- 
formers 

Total  Per- 
formers 

Performing 
Sires  and  Get 

Geo.  Wilkes  ('s6-'82)    .  . 

83 

102 

2410 

96 

I63 

2573 

40-1501 

Hambletonian  10  ('49~'76) 

40 

ISO 

1694 

80 

117 

1811 

8-  174 

Electioneer  ('68-'9o)  .  .  . 

1  60 

97 

942 

79 

I03 

1045 

60-   723 

Nutwood  ('70-     )  

I65 

132 

693 

"3 

184 

877 

55-  29[ 

Belmont  ('64~'89)  

CQ 

74 

6i"5 

66 

no 

72C. 

25-    742 

Almont  ('64—  '84) 

•57 

06 

c,6o 

81 

I7O 

600 

14-    212 

Red  Wilkes  ('74-    )   .  .  . 

157 

93 

47i 

79 

116 

587 

S^-  374 

Onward  ('7  <;—     }  . 

i<;8 

1  06 

4^4 

1:7 

QI 

C4C 

34-  228 

1  Column  i,  name  of  grandsire  ;  column  2,  number  of  performers  of  his  ffivn 
get ;  columns  3  and  4,  number  of  sires  he  got,  with  their  get  in  the  list ;  columns 
5  and  6,  number  of  dams  he  got,  with  the  performers  dropped  by  them  ;  column  7, 
total  performers  gotten  by  sires  and  dams,  —  the  second  generation ;  column  8, 
number  of  performers  (column  2)  that  were  also  sires,  and  their  performing  get. 

N.B.  Many  of  the  sires  (column  3)  were  not  performers  and  many  of  the 
performers  (column  2)  were  not  sires.  Numbers  in  parentheses  refer  to  year  of 
birth  and  death. 


PREPOTENCY 


557 


Breeders  of  speed  and  breeders  of  breeders.  Nothing  more 
forcibly  strikes  the  student  working  with  records  of  this  kind 
than  the  fact  that  some  sires  are  notably  sires  of  speed  which 
ends  in  that  generation,  while  others,  not  specially  noteworthy 
for  getting  performers  themselves,  yet  produce  sires  and  dams 
of  extreme  breeding  power.  See  the  following  table,  which  is  a 
table  of  famous  producers  of  speed,  and  compare  with  the  last 
table,  which  is  a  table  of  famous  producers  of  producers.  Especial 
attention  is  called  in  this  connection  to  Wilton,  Simmons,  and 
Pilot  Medium,  —  famous  getters  of  speed,  —  as  compared  with 
Almont,  Belmont,  Hambletonian,  and  Geo.  Wilkes,  —  none  of 
them  famous  as  direct  producers  of  speed,  but  all  phenomenal 
breeders  of  sires  and  dams  of  speed. 

TABLE  OF  FAMOUS  SIRES  AND  THEIR  DESCENDANTS  ;  BEING  ALL  THAT 
SIRED  100  PERFORMERS  OR  OvER1 


X 

a 

3 

4 

5 

6 

7 

8 

Name 

Per- 
formers 

Sires 

Per- 
formers 

Dams 

Per- 
formers 

Total  Per- 
formers 

Performing 
Sires  and  Get 

Baron  Wilkes  ('82-     )  .  . 

99 

26 

94 

21 

23 

117 

21-  85 

Gambetta  Wilkes  ('81-    ) 

IOI 

30 

III 

17 

23 

«34 

ii-  43 

Wilton  ('80-     )  

IQ7 

I  7. 

•JQ 

I  7 

A-J 

ii     28 

V 

1  3 

^3 

Simmons  ('79-     )  

I°5 

26 

63 

14 

18 

81 

J3-  54 

Pilot  Medium  ('79-     )  .  . 

114 

17 

32 

23 

33 

65 

12-    23 

Alcantara  ('76-    )  

149 

43 

200 

27 

45 

3i5 

19-111 

Red  Wilkes  ('74-     )  .  .  . 

157 

93 

471 

79 

116 

587 

56-374 

Onward  ('75-     )  

158 

1  06 

454 

57 

91 

545 

34-228 

Electioneer  ('68-'9o)   .  .  . 

1  60 

97 

942 

79 

103 

1045 

60-723 

Nutwood  ('70—     ) 

i6c 

I  72 

607 

iii 

184 

887 

r  e    -7QT 

»*o 

1  3* 

uyj 

1  1  3 

jj   ~yl 

Attention  is   especially  called   to   column   7,   recording  the 

second  generation  of  performers,  as  compared  with  column  2, 

—those  gotten  directly.   It  will  be  noted  of  three  famous  stallions 

that  they  were  represented  by  fewer  performers  in  the  second 

1  This  table  is  made  up  on  exactly  the  same  plan  as  the  previous  table ;  it 
is  designed  to  be  studied  in  connection  with  the  former,  to  show  the  difference 
between  breeders  of  speed  and  breeders  of  breeders.  Years  are  denoted  by  figures 
in  parentheses. 


558  TRANSMISSION 

generation  than  in  the  first,  but  also  that  their  age  is  against 
their  second-generation  record. 

Relation  between  performance  and  breeding  powers.  An  at- 
tempt was  made  to  learn  whether  performers  are  better  breeders 
than  non-performers.  There  were  at  that  time  49  stallions  in 
the  2:10  list.  Only  21  of  these  had  get  in  the  2:30  list,  and 
only  four  had  produced  sires  of  speed. 

The  breeding  record  of  this  class  of  stallions  looks  pitifully 
slim  as  compared  with  that  of  the  great  breeders.  The  best 
breeding  record  made  by  a  horse  in  the  2:10  list,  up  to  the 
time  these  studies  were  made,  was  that  of  Nelson  4209,  who 
had  produced  28-12  p.,  eight  sires  (5-7  p.),  and  three  dams 
(1-2  p.).  The  whole  49  in  the  2:10  list  had  produced  only 
194-65  p.,  and  only  13  sires  of  speed,  8  of  which  have  just  been 
credited  to  Nelson. 

We  might  conclude  that  performance  is  not  a  very  good  index 
of  breeding  power,  but  it  would  be  a  hasty  conclusion  if  made 
on  this  basis.  Two  circumstances  conspire  to  keep  down  the 
breeding  record  of  stallions  of  extreme  speed.  One  of  these  is 
the  fact  that  many  of  them  are  young,  and  the  other  is  the  fact 
that  a  horse  capable  of  making  low  records  is  worth  more  for 
racing  than  for  breeding  purposes,  and  while  racing  engagements 
do  not  absolutely  prevent  breeding  among  stallions,  as  it  does 
among  mares  until  their  racing  days  are  over,1  yet  it  operates 
to  greatly  reduce  it.  Evidently  we  shall  get  little  light  on  our 
question  from  this  source. 

Turning  to  individuals,  we  find  that  Nutwood  600,  the  great- 
est sire  of  speed  (see  table  on  page  555),  had  a  record  of  2:18  f, 
but  that  Electioneer,  the  next  greatest  sire  of  speed,  had  no 
record.  Of  the  "  big  ten,"  but  one  has  a  record  as  good  as 
2:18,  and  his  breeding  record  is  the  lowest  of  the  lot. 

Turning  to  the  greatest  grandsires  of  speed,  Geo.  Wilkes 
heads  the  list  with  a  record  of  2:22,  but  Hambletonian  10 
comes  next,  having  produced  more  sires  of  speed  than  any  horse 

1  There  were  also  49  mares  in  the  2:10  list,  —  a  strange  coincidence,  —  not 
one  of  whom  had  produced  anything  in  the  list.  This  fact  is,  of  course,  not  to  be 
construed  to  mean  that  they  could  not  produce  speed,  but  rather  that  they  have 
not,  as  a  class,  had  the  opportunity.  What  kind  of  brood  mares  they  would  make 
when  tried  is  another  question. 


PREPOTENCY  559 

living  or  dead,  and  he  has  no  record;1  Electioneer  125  comes 
next,  also  with  no  record;  then  Nutwood,  2:i8|  ;  Belmont,  no 
record;  followed  by  Almont,  2:39!;  ^Q^  Wilkes,  2:40;  and 
Onward,  2:25!. 

From  this  showing  of  individuals  we  can  argue  either  that  the 
great  breeders  were  too  busy  to  make  racing  records  or  that 
breeding  power  is  independent  of  the  ability  to  perform. 

Neither  conclusion  is  warranted.  In  the  first  place,  the  breed- 
ing record  of  a  stallion  with  a  track  record  is  injured  by  the 
fact  that  he  has  little  opportunity  until  his  racing  days  are 
over ;  but  it  is  helped  by  the  fact  that  when  he  is  sent  to  the 
stud  he  has  a  superior  class  of  mares. 

Again,  it  does  not  follow,  if  a  horse  has  not  made  a  track 
record,  that  he  should  be  considered  as  unable  to  do  it.  It  may 
be  from  some  slight  defect  or  from  lack  of  proper  training,  from 
some  minor  injury,  or  from  one  or  more  of  a  hundred  other 
causes  having  no  connection  whatever  with  his  inherited  ability 
to  go. 

Evidently,  if  we  are  to  get  any  light  upon  this  question  from 
this  source,  —  and  it  ought  to  be  one  of  the  best  of  sources  for 
information  of  this  class,  —  then  we  must  obtain  it  from  large 
numbers,  in  which  the  breeding  record  of  those  known  to  be 
performers  is  compared  directly  with  that  of  those  that  have  no 
performance  record. 

Accordingly  a  table  was  prepared  exhibiting  the  breeding 
record  of  165  of  the  principal  stallions.  They  were  chosen  from 
the  list  of  207  that  had  produced  ten  or  more  sires  of  speed  or 
ten  or  more  dams  of  speed,  and  included  all  individuals  that  Jiad 
produced  both  performing  and  non-performing  sires?  except  a  very 
few,  the  data  for  which  were  incomplete.  The  table  shows,  first 
(column  i),  the  total  number  of  performers  produced  by  the 

1  It  was  popularly  believed  that  Hambletonian  10  could  go  in  about  2:40,  but 
he  was  dead  long  before  anybody  knew  his  value  as  a  breeder  of  speed. 

2  By  "  performers  "  is  meant  those  that  have  a  track  record  of  2:30,  or  better. 
The  term  "non-performers"  covers  all  without  a  record;  it  manifestly  includes 
two  classes,  —  those  that  might  have  made  a  record  under  suitable  circumstances 
and  those  that  could  not  have  done  so  under  any  circumstances.    As  there  is  no 
way  of  distinguishing  between  these  two,  they  are  all  called  non-performers,  and 
the  table  makes  a  comparison  between  those  that  have  made  a  record  and  all  others, 
able  or  unable,  that  have  not  done  so. 


560 


TRANSMISSION 


various  stallions  without  regard  to  their  breeding  powers ; 
second  (columns  2  and  3),  the  number  of  performing  sires  (that 
is,  sires  with  speed  records  2  :  30  or  better),  with  their  get ; 
third  (columns  4  and  5),  the  number  of  non-performing  sires, 
with  their  get.  For  convenience  there  is  added  (column  6)  the 
track  record  of  those  stallions  (of  the  165)  which  were  themselves 
"  performers  ";  for  example,  line  6:  this  sire  made  a  record  of 
2:23  on  the  track.  He  produced  149  performers,  19  perform- 
ing sires  that  got  1 1 1  performers,  and  24  sires  that  never  made 
a  record  on  the  track  but  that  produced  89  offspring  that  were 
performers.  The  entire  table,  covering  165  individuals,  is  given 
in  order  that  the  reader  may  have  at  hand  the  me'ans  of  making 
individual  comparisons,  many  of  which  are,  to  say  the  least, 
remarkable.  Names  have  been  omitted,  but  the  reader  may  be 
interested  to  know  that  line  65  is  Geo.  Wilkes,  70  is  Hamble- 
tonian  10,  120  is  Nutwood,  and  121  is  Onward. 

BREEDING  RECORD  OF  165  LEADING  STALLIONS  TO  SHOW  THE  RELATION 
BETWEEN  ''PERFORMANCE  AND  BREEDING"  POWERS 


i 

2 

3 

4 

5 

6 

Performing 
Get 

Sires  also 
Performers 

Performing 
Get 

Sires  not 
Performers 

Performing 
Get 

Record 

I 

5 

2 

12 

12 

144 

2 

4 

I 

3 

4 

6 

2:30 

3 

53 

9 

29 

23 

70 

4 

16 

3 

12 

17 

37 

2:29^ 

5 

55 

3 

26 

5 

ii 

6 

149 

19 

III 

24 

89 

2:23 

7 

59 

27 

208 

21 

I05 

2:27 

8 

8 

3 

9 

5 

.11 

2:24X 

9 

92 

i 

2 

i 

i 

2  :  09X 

10 

6 

i 

3 

3 

3 

2:25 

ii 

37 

14 

212 

82 

357 

2  :  29^ 

12 

20 

4 

19 

9 

26 

2:29 

'3 

47 

i 

I 

6 

9 

2:26 

14 

5 

i 

I 

3 

3 

15 

47 

6 

12 

4 

8 

2:26^ 

16 

31 

9 

31 

12 

17 

2:2iX 

17 

30 

7 

25 

5 

12 

2:27^ 

18 

46 

6 

40 

3 

5 

2:l6X 

PREPOTENCY 


561 


i 

2 

3 

4 

5 

6 

Performing 
Get 

Sires  also 
Performers 

Performing 
Get 

Sires  not 
Performers 

Performing 
Get 

Record 

19 

32 

I 

I 

4 

4 

20 

3 

I 

7 

I 

I 

21 

66 

6 

20 

2 

5 

2  :  17^ 

22 

19 

2 

8 

7 

10 

23 

65 

5 

8 

2 

2 

2  :  12 

24 

99 

21 

85 

5 

9 

2:18 

25 

17 

IO 

32 

13 

28 

26 

15 

3 

3 

10 

16 

27 

59 

25 

342 

49 

273 

28 

36 

5 

9 

5 

17 

2:29 

29 

8 

i 

i 

i 

i 

3° 

9 

4 

ii 

9 

13 

31 

6 

2 

6 

4 

7 

2:22^ 

32 

60 

5 

9 

42 

119 

33 

92 

15 

83 

10 

20 

34 

25 

2 

6 

i 

i 

2:  i9# 

35 

45 

10 

52 

4 

13 

2  :  12^ 

36 

9 

I 

i 

3 

3 

2:28 

37 

4 

3 

22 

13 

33 

38 

55 

2 

IO 

4 

10 

2:18 

39 

17 

I 

7 

18 

29 

2  :  22 

40 

14 

2 

8 

4 

6 

41 

38 

7 

88 

28 

65 

42 

35 

2 

3 

6 

8 

43 

54 

3 

5 

i 

6 

44 

57 

21 

71 

34 

189 

45 

51 

10 

67 

16 

32 

46 

18 

4 

ii 

3 

8 

2:2334: 

47 

16 

4 

13 

7 

9 

V 

48 

13 

2 

66 

10 

45 

49 

85 

23 

93 

15 

16 

5° 

1  60 

60 

723 

37 

219 

51 

33 

I 

i 

4 

7 

52 

65 

I 

i 

i 

2 

2:25^ 

53 

4 

I  • 

i 

4 

5 

2  :  29 

54 

24 

I 

i 

i 

2 

2  :  28# 

55 

6 

I 

i 

3 

8 

^ 

56 

25 

2 

3 

i 

2 

2  :  _$# 

57 

22 

3 

7 

3 

4 

2:30 

58 

15 

3 

5 

ii 

.  .1    • 

__  _____ 

562 


TRANSMISSION 


X 

a 

3 

4 

5 

6 

Performing 
Get 

.Sires  also 
Performers 

Performing 
Get 

Sires  not 
Performers 

Performing 
Get 

Record 

59 

IOI 

II 

43 

19 

68 

2:22/2 

60 

20 

7 

19 

IO 

15 

61 

15 

6 

H 

26 

8l 

62 

15 

5 

21 

3 

31 

63 

4 

2 

II 

12 

•52 

2-.23y2 

64 

10 

I 

9 

IO 

'9 

65 

83 

40 

1501 

62 

909 

2  I  22 

66 

4 

I 

2 

17 

33 

67 

38 

8 

43 

15 

47 

2  :2oy2 

68 

12 

6 

17 

3 

5 

2:2714: 

69 

75 

ii 

85 

16 

33 

2:  15^ 

70 

40 

8 

174 

142 

2520 

71 

24 

3 

8 

9 

32 

'   72 

'5 

2 

4 

9 

'9 

73 

28 

6 

32 

*} 

3 

2:26^ 

74 

23 

i 

4 

3 

7 

75 

i5 

i 

14 

4 

ii 

76 

23 

i 

5 

4 

6 

77 

46 

8 

74 

9 

40 

2:2lX 

78 

3° 

2 

5 

4 

4 

79 

94 

34 

'55 

31 

205 

80 

9 

15 

96 

29 

154 

81 

4 

i 

6 

H 

36 

2:29 

82 

5 

i 

22 

i 

8 

83 

18 

7 

2O 

4 

6 

84 

10 

4 

9 

2 

2 

2:21 

85 

20 

i 

I 

I 

4 

2  :28 

86 

7 

3 

12 

7 

25 

87 

85 

u 

172 

ii 

12 

88 

29 

8 

19 

7 

29 

2:21^ 

89 

38 

i 

2 

7 

12 

2:16^ 

90 

8 

i 

12 

6 

8 

9i 

2 

i 

4 

4 

5 

92 

41 

5 

43 

21 

1  06 

93 

40 

13 

32 

IO 

18 

94 

II 

i 

7 

10 

19 

95 

4 

i 

10 

5 

6 

96 

4 

i 

21 

3 

7 

97 

21 

2 

7 

3 

4 

98 

31 

5 

28 

12 

42 

PREPOTENCY 


563 


i 

2 

3 

4 

5 

6 

Performing 
'Get 

Sires  also 
Performers 

Performing 
Get 

Sires  not 
Performers 

Performing 
Get 

Record 

99 

31 

7 

63 

12 

88 

IOO 

24 

3 

7 

4 

9 

2  :  21 

101 

7 

2 

6 

6 

8 

1  02 

17 

I 

2 

7 

9 

103 

13 

2 

3 

2 

4 

2:26^ 

104 

6 

I 

'3 

22 

83 

105 

47 

4 

ii 

7 

J3 

2:21^ 

1  06 

6 

2 

1  1 

4 

IO 

107 

60 

9 

IO2 

12 

'9 

1  08 

25 

5 

24 

52 

158 

109 

9 

2 

9 

14 

43  . 

IIO 

17 

7 

65 

IO 

28 

III 

15 

i 

i 

2 

2 

I  12 

28 

4 

6 

'5 

39 

U3 

IO 

i 

4 

5 

19 

114 

16 

2 

4 

4 

8 

115 

23 

7 

52 

1  8 

51 

116 

M 

3 

19 

3 

21 

117 

25 

3 

3 

2 

7 

118 

5 

2 

25 

6 

6 

119 

70 

3 

9 

5 

22 

120 

165 

55 

291 

77 

402 

2  :  18^ 

121 

158 

34 

228 

72 

226 

2  :  25^ 

122 

'5 

i 

4 

3 

4 

123 

24 

i 

4 

5 

IO 

124 

25 

3 

ii 

9 

32 

2  :  r3^ 

125 

1  1 

4 

8 

3 

9 

2:26X 

126 

25 

6 

15 

i 

i 

2  :  I7X 

I27 

8 

i 

5 

5 

27 

128 

5 

i 

3 

2 

2 

129 

104 

12 

23 

5 

9 

I30 

21 

2 

3 

8 

40 

'31 

51 

T3 

I25 

27 

55 

132 

57 

2 

3 

i 

2 

2  :  2I# 

'33 

'57 

56 

374 

37 

97 

'34 

92 

15 

64 

H 

89 

2:I7X 

'35 

18 

3 

99 

3 

4 

2  :  I7X 

136 

6 

3 

M 

13 

31 

'37 

4 

i 

2 

3 

4 

138 

8 

4 

35 

7 

1  1 

2:29^ 

1  1  

5^4 


TRANSMISSION 


i     . 

a 

3                         4 

5 

6 

Performing 
Get 

Sires  also 
Performers 

Performing 
Get 

Sires  not 
Performers 

Performing 
Get 

Record 

139 

96 

9 

32 

6 

8 

2:  I9# 

140 

12 

2 

6 

IO 

17 

2:i5X 

141 

4 

I 

2 

i 

I 

142 

85 

4 

4 

.     5 

6 

143 

24 

6 

16 

4 

6 

144 

13 

2 

7 

i 

3 

2:26^ 

145 

34 

3 

28 

i 

i 

2:25^ 

146 

88 

13 

85 

25 

54 

147 

52 

ii 

78 

IO 

20 

2:24 

148 

42 

i 

i 

4 

ii 

149 

48 

ii 

38 

27 

55 

150 

22 

2 

'3 

2 

2 

2:27 

151 

IO 

I 

I 

8 

24 

2:22^ 

'52 

15 

3 

5 

9 

73 

153 

T5 

i 

2 

7 

ii 

154 

3i 

7 

48 

12 

33 

155 

34 

5 

14 

36 

142 

156 

ii 

3 

IO 

I 

4 

*57 

35 

7 

42 

9 

16 

2:19 

158 

i 

i 

I 

i 

i 

159 

65 

7 

39 

5 

12 

2:24^ 

160 

IO 

3 

82 

9 

21 

161 

103 

ii 

28 

2 

2 

2:  i9# 

162 

13 

5 

61 

2O 

I05 

2:21^ 

163 

38 

4 

IO 

2 

3 

164 

45 

7 

27 

II 

29 

165 

32 

2 

3 

4 

6 

2:28X 

5688 

1062 

7843 

1941 

9186 

What  light,  now,  does  this  throw  upon  our  query  ?  We  re- 
member the  disadvantage  occasioned  to  the  performing  sire  by  the 
interference  of  track  engagements  during  his  racing  years,  and 
we  remember,  on  the  other  hand,  the  advantage  that  comes  from 
his  enhanced  reputation  and  the  superior  class  of  mares  offered. 

This  table,  taken  as  a  whole,  shows  that  these  165  leading 
stallions  (being  the  ones  of  highest  note  that  produced  both  per- 
forming and  non-performing  sires)  produced  5688  offspring  and 
17,029  grand  offspring  with  track  records  of  2:30  or  better. 


PREPOTENCY  565 

This  is  an  average  of  34.5  direct  get,  and  the  grand-get  (17,029) 
covers  two  thirds  of  all  in  the  list  (26,327).  It  is,  therefore,  the 
very  cream  of  the  breed.  What,  now,  is  the  breeding  record  of 
the  performing  sires  of  this  list  as  compared  with  that  of  the 
non-performing  ? 

The  non-performing  sires  (1941,  column  4)  are  almost  double 
the  number  of  the  performing  sires  (1062,  column  2).  These 
1941  non-performing  sires  produced  a  total  of  9186  performers, 
—  a  ratio  of  4.7  each;  while  the  1062  performing  sires  pro- 
duced in  all  7843  performers,  —  a  ratio  of  7.4  each. 

If  any  difference  in  breeding  powers  is  correlated  with  high 
speed,  it  would  be  reduced  rather  than  exaggerated  in  this  table, 
for  the  list  of  what  are  called  non-performers  clearly  includes  a 
good  many  potential  performers  that  had  the  inherent  ability  to 
"  go  "  if  all  conditions  had  been  favorable. 

At  the  same  time  it  must  not  be  forgotten  that  the  non-per- 
forming sires  on  this  list  are  of  the  same  blood  lines  as  are  'the 
performing  sires,  being  in  every  case  at  least  half-brothers  out  of 
the  same  sire.1  To  the  writer  the  conclusion  seems  inevitable 
that  the  heavy  difference  of  7.4  against  4.7  apiece  is  in  a  large 
sense  correlated  with  the  individual  ability  to  "  perform." 

Turning  to  individual  cases,  we  find  that  the  performing  sires 
got  by  Geo.  Wilkes  (line  65)  produced  on  an  average  37.5 
performers  apiece  (1501-^40),  while  his  non-performing  sires 
produced  an  average  of  only  14.6  (909  -5-  62),  although  the  popu- 
larity of  Wilkes'  blood  was  enough  to  assure  almost  any  son  of 
his  a  "good  chance." 

Nutwood  (line  120),  the  greatest  sire  of  speed,  produced  55 
performing  sires  and  77  «<w-performing  sires.  The  first  produced 
at  the  rate  of  5.3  (291  -s-  55)  and  the  second  at  the  rate  of  5.2 
(402  -j-  77),  — almost  exactly  the  same.  Onward  (line  121)  pro- 
duced 34  performing  sires  and  72  non-performing.  The  first 
produced  performers  at  the  rate  of  6.7  each,  the  second  at  the 
rate  of  3.1. 

Hambletonian  10  (line  70),  the  most  successful  producer  of 
racing  blood  and  the  foundation  of  almost  all  modern  blood  lines, 

1  The  table  is  confined  to  those  stallions  that  produced  both  performing  and 
non-performing  sires. 


566  TRANSMISSION 

produced  only  40  performers  and  8  performing  sires,  but  Geo. 
Wilkes  was  one  of  these,  and  the  average  of  21.7  (174-5-8)  tells 
but  a  small  part  of  the  story  of  these  8  performing  sires  of  this 
remarkable  progenitor  of  speed.  His  142  non-performing  sires 
produced  speed  at  an  average  of  17.7  each.  It  would  be  an 
interesting  study  to  determine  how  the  descendants  of  these 
142  non-performing  sires  compared  with  those  of  the  8  perform- 
ing sires,  —  a  study  that  the  writer  has  left  to  others  1  or  to  a 
future  time. 

A  conservative  conclusion  from  these  data  would  be  that  per- 
formance is  not  an  invariable  index  of  breeding  powers  but  that 
on  the  average  the  performers  are  much  more  likely  to  get  speed 
than  are  non-performers  of  the  same  breeding. 

This  difference,  if  it  really  exists,  is  without  doubt  inherent; 
indeed,  it  is  not  difficult  to  find  instances  in  which  that  which 
seems  to  be  the  general  principle  is  reversed,  so  that  the  non- 
performers  are  the  better  breeders  (see  lines  I,  44,  62,  79,  130, 
and  155).;  all  of  which  shows  that  while  good  negative  testimony 
may  be  found  in  a  single  instance,  positive  statements  must  be 
based  upon  a  comprehensive  study  of  large  numbers.  And  so 
we  need  to  go  through  our  records  and  our  experience  carefully, 
hunting  for  the  things  that  constitute  ground  on  which  pre- 
potency may  safely  be  predicated.  Without  doubt  purity  of 
blood,  in  the  sense  of  the  highest  possible  percentage  of  diameters 
favorable  to  the  purpose  desired,  unalloyed  by  disturbing  factors, 
will  be  found  to  constitute  the  real  basis  of  prepotency.  When 
discussing  the  mathematics  of  breeding  it  was  found  that,  no 
matter  what  the  combinations,  a  few  individuals  will  always 
remain  pure.  By  the  same  process  of  reasoning,  when  we  mix 
the  elements  of  desirable  characters,  diluting  them  as  little  as 
possible  with  "  wild  blood,"  we  shall,  by  the  same  law  of  prob- 
abilities, once  in  a  while  effect  a  phenomenal  combination.  Such 
a  one  is  produced  by  methods  not  under  our  control,  except  as 
we  increase  the  probability  by  increasing  the  intensity  of  breeding. 
This  is  the  very  heart  and  soul  of  "line  breeding,"  and  means 
that  the  best-bred  animal  is  the  most  likely  to  be  prepotent.  In 

1  Work  of  this  kind  runs  into  days,  weeks,  and  months,  at  a  surprising  rate. 
The  data  given  here  represent  many  months  of  laborious  work. 


PREPOTENCY  567 

the  meantime  it  will  be  well  to  remember  that,  to  the  best  of  our 
present  knowledge,  some  individuals  seem  to  be  preeminently 
breeders  of  performers  ;  others,  breeders  of  sires  ;  and  still  others, 
breeders  of  dams  ;  while  a  few  are  breeders  of  all  three  classes. 

Importance  of  the  actual  test.  The  student  cannot  fail  to  note 
that  the  bulk  of  the  business 'of  real  improvement  is  done  by  a 
very  few  really  great  animals,  and  that  the  work  of  most  of  the 
so-called  breeding  stock  is  merely  that  of  reproduction  in  the 
sense  of  increase  of  numbers. 

It  is  perfectly  clear  that  he  who  is  bent  upon  accomplishing 
real  results  will  seek  for  the  occasional  phenomenal  breeder, 
and,  having  found  him,  will  make  the  most  of  him  while  he  is 
able  to  reproduce.  It  is  matter  of  deep  regret  that  so  many  of 
our  phenomenal  animals,  like  Hambletonian  10,  were  never 
recognized  as  such  until  long  after  they  were  dead  and  the 
opportunity  to  utilize  them  to  the  best  advantage  had  passed 
forever,  leaving  us  to  do  the  best  we  can  and  make  the  most  of 
the  "  accidents  "  that  are  left  behind. 

In  seeking  these  phenomenal  breeders  too  much  cannot  be 
said  concerning  the  importance  of  the  actual  breeding  test  as 
the  last  and  final  criterion  of  breeding  powers,  —  a  subject  on 
which  more  will  be  said  later. 

SECTION  II  —  PREPOTENCY  IN  SEX 

There  is  a  traditional  belief  that  in  general  the  sire  is  pre- 
potent over  the  dam.  In  actual  practice  this  is  likely  to  be  the 
case,  for  the  sire  is,  in  most  cases,  the  better  bred  of  the  two 
parents.  If  a  breeder  starts  out  to  breed  half  bloods,  and  to  give 
his  stock  the  most  benefit  possible  of  good  blood  at  the  least 
expense,  he  will  of  course  provide  it  through  the  male  side ;  for 
with  one  male  he  can  influence  the  blood  of  many  offspring, 
while  with  the  female  he  can  influence  but  one  in  horses  or 
cattle,  and  but  few  in  swine.  So  it  comes  about,  for  purely 
economic  reasons  alone,  that  in  general  sires  are  better  bred 
than  dams,  and  on  this  account  should  be  prepotent. 

But,  the  question  of  breeding  aside,  are  they  prepotent  be- 
cause of  sex  ?  On  this  point  speculation  has  long  been  at  work, 


568  TRANSMISSION 

resulting  in  a  choice  collection  of  "  beliefs,"  covering  about  all 
the  combinations  possible.    It  is  held  : 

1.  That  the  male  is  prepotent  on  general  principles,  because 
males  are  stronger  and  more  virile  than  females. 

2.  That  the  female  is  prepotent,  especially  among  mammals, 
because  her  associations  with  the  offspring  are  so  much  more 
intimate,  both  physiologically  and  socially. 

3.  That  that  parent   is   prepotent    which  has   the    stronger 
nervous  and  sexual  organization,  —  whatever  that  may  mean. 

4.  That  the  male  is  prepotent  over  the  forward  and  upper 
parts  of  the  body  and  the  mental  qualities. 

5.  That  the  exact  reverse  of  the  last  statement  is  the  truth. 

6.  That  the  male  governs  the  external  and  the  female  the 
internal  organs  and  parts. 

Instances  are  not  wanting  to  "  prove  "  any  of  these  beliefs ; 
indeed,  proof  by  the  method  of  instance  is  the  favorite  form  of 
argument  for  or  against  any  one  of  them,  and  it  is  not  too  much 
to  say  that  by  this  method  these  or  any  other  assumptions  may 
be  readily  substantiated. 

We  have  learned  long  ago  the  unreliability  of  conclusions  of 
this  kind,  and  it  is  worth  while  to  distinguish  clearly,  so  far  as 
we  are  able,  between  what  is  known  and  what  has  not  yet  been 
learned  touching  this  important  matter. 

In  general  the  sexes  are  equipotent.  So  far  as  is  now  known, 
no  part  of  the  germ  cell  is  naturally  predestined  to  provide  any 
particular  part  of  the  body.  The  germ  cells  from  both  parents 
are  bearers  of  the  hereditary  substance  in  the  proportion  in 
which  they  possess  it,  and  either  sex  may  and  does  transmit 
any  and  all  the  characters  of  the  race  to  its  offspring  of  either 
sex.  We  may  say  then,  in  general,  that  that  parent  will  be 
prepotent  whose  hereditary  substance  is  least  mixed  and,  there- 
fore, most  intensified  along  the  line  of  established  characters. 
The  only  way  we  can  go  farther  than  the  general  principle  just 
stated  is  by  extensive  studies  solving  the  coefficient  of  heredity 
between  each  parent  and  its  offspring  of  both  sexes  for  different 
characters  separately. 

This  has  been  done  for  a  number  of  characters,  both  in  men 
and  in  animals,  though  the  list  is  too  small  to  do  more  than  to 


PREPOTENCY 


569 


indicate  the  direction,  without  showing  the  limits,  of  prepotency. 
The  following  list  from  Pearson 1  includes  the  most  accessible 
data  co-vering  this  point.  Unfortunately  again,  much  of  the 
material  is  drawn  from  studies  in  man,  but  fortunately  also 
horses  and  dogs  have  been  included  to  some  extent.  It  is  all 
useful  in  showing  the  mixed  nature  of  prepotency. 

TABLE  ILLUSTRATING  PREPOTENCY  OF  SEX 


RELATIONSHIP 

MATERIAL 

CHARACTER 

COEFFICIENT 

OF 

HEREDITY 

J 

Father  and  son 

English    

Stature    .  .  . 

.^06 

2 

Father  and  daughter 

English 

Stature 

76o 

9 

Mother  and  son  .  . 

English    

Stature    .  .  . 

102 

Mother  and  daughter 

English 

Stature 

•ju^ 
284 

s 

6 

7 

8 

Mother  and  son  .... 
Mother  and  daughter  . 
Sire  and  foal  
Dam  and  foal 

American  Indians    .  . 
American  Indians    .  . 
Thoroughbred  horses 
Thoroughbred  horses 

Head  index  . 
Head  index  . 
Coat  color.  . 
Coat  color 

.^04 
•370 
.300 

•517 
C27 

Q 

Sire  and  offspring 

Basset  hound  

Coat  color  .  . 

•J*/ 

1  77 

IO 

Dam  and  offspring    .  . 

Basset  hound  

Coat  color  .  . 

C24. 

I  I 

Brother  and  brother 

English       

Stature    .  .  . 

•JQl 

12 

Colt2  and  colt  

Thoroughbred  horses 

Coat  color  .  . 

•jyl 
.621 

I  "? 

Sister  and  sister  . 

English       

Stature    .  .  . 

.A  A  A 

14 

Filly  2  and  filly  

Thoroughbred  horses 

Coat  color  .  . 

.603 

I  e 

Brother  and  sister 

English    

Stature    .  .  . 

.77C 

16 

Colt  and  filly 

Thoroughbred  horses 

Coat  color  .  . 

•&->> 

Here,  in  small  compass,  are  results  of  studies  sufficiently 
extensive  to  justify  careful  consideration.  The  following  con- 
clusions are  certainly  warranted  : 

i .  The  English  father  is  prepotent  over  the  mother  in  respect 
to  stature  in  both  sexes  (see  lines  i,  2,  3,  4) ;  but  the  reverse  is 
true  as  to  coat  color  in  thoroughbred  horses  and  in  Basset 
hounds,  especially  in  the  latter  (see  lines  7,  8,  9,  10).  The  con- 
clusion of  all  this  is  that  sometimes  one  sex  is  prepotent  and 
sometimes  the  other,  and,  accordingly,  that  each  character  must 
be  worked  out  by  itself  and  for  each  race  separately. 

1  Pearson,  Grammar  of  Science,  pp.  458,  461. 

2  By  "colt  "  is  of  course  meant  a  male  foal,  and  by  "  filly"  a  female  foal. 


570  TRANSMISSION 

2.  To  quote  Pearson,  the  male  seems  to  " inherit  more"  than 
the  female  because  his  coefficient  of  heredity  is  higher,  with 
whichever  parent  the  comparison  is  made  (compare  lines  i,  3,  5, 
with  lines  2,  4,  6).    This  conclusion  Pearson  declares  is  con- 
firmed by  data  in  eye  color,  as  well  as  in  stature,  coat  color,  and 
head  index.1 

It  is  a  significant  fact  that  for  the  races  and  characters  here 
involved  the  correlation  between  brother  and  brother  is  less  than 
the  correlation  or  similarity  between  sister  and  sister  (compare 
lines  ii  and  12  with  lines  13  and  14),  which  means  also  that 
sisters  resemble  each  other  more  closely  than  do  brothers. 

3.  The  resemblance  between  members  of  the   same  sex  is 
closer  than  that  between  members  of  opposite  sexes  (compare 
lines  ii  and  13  with  line  15  ;  also  12  and  14  with  16).    Pearson 
also  declares  that  the  same  principle  holds  for  eye  color  and 
head  index,  and  he  is  inclined  to  believe  it  general.2 

This  author  points  out  that  this  principle,  if  general,  means 
that  "  inheritance  in  a  line  through  one  sex  is  prepotent  over 
inheritance  in  the  same  degree  with  a  change  of  sex  "  ;  that  is, 
that  inheritance  tends  to  run  in  sex  lines,  which  means,  to 
quote  Pearson  (italics  and  parentheses  mine),  "  that  a  man  in  eye 
color  (for  example)  more  clearly  resembles  his  paternal  than  his 
maternal  grandfather  (or  other  male  ancestors) ;  a  woman  more 
closely  resembles  her  maternal  grandmother  than  her  paternal 
grandmother.  Again,  a  nephew  is  more  like  his  paternal  uncle 
than  his  paternal  aunt ;  a  niece,  like  her  maternal  aunt  than  her 
maternal  uncle."  3 

Future  investigations  will  add  to  our  knowledge  in  these 
matters,  and  perhaps  modify  some  general  statements  now  con- 
sidered safe,  but  the  matter  as  stated  above  represents  the  best 
conclusions  of  those  who  have  given  most  careful  attention  to 
the  subject  up  to  the  present  time. 

Comparative  variability  of  the  sexes.  There  has  been  a 
general  tendency  to  assert  that  males  are  more  variable  than 
females.4  This  assertion  has  not  been  based  on  actual  studies 

1  Pearson,  Grammar  of  Science,  p.  459.  2  Ibid.  p.  459.  8  Ibid.  p.  460. 

4  See  Geddes  and  Thomson,  Evolution  of  Sex,  pp.  12-13;  Darwin,  Animals 

and  Plants  under  Domestication,  I,  457  ;  Pearson,  Chances  of  Death,  pp.  256-260. 


PREPOTENCY  571 

but  upon  the  theoretical  ground  that  males  lead  a  more  active 
life  and  take  the  lead  in  sexual  selection.  The  data  just  cited 
seem  to  substantiate  this  assertion.  For  the  species  and  charac- 
ters involved  it  appears  that  male  offspring  follow  more  closely 
the  parental  type  than  do  the  female,  and  (which  amounts  to 
the  same  thing)  female  offspring,  or  sisters,  are  more  nearly  alike 
than  are  male  offspring,  or  brothers,  —  tending  to  the  conclusion 
that  males  are  more  variable  than  females. 

Pearson,1  however,  records  data  of  an  exceedingly  exhaustive 
series  of  investigations  of  variability  in  men  and  women,  not 
absolutely  but  relatively,  as  expressed  in  the  coefficient  of 
variability.2  While  he  finds  men  more  variable  at  certain  ages 
and  in  certain  characters,  yet  he  does  not  find  pronounced  and 
decided  differences,  nor  are  these  the  same  for  different  races 
of  men.  He  concludes,  on  the  whole,  that  for  all  races  studied, 
ancient  and  modern,  and  for  all  characters  covered  by  the 
studies,  there  is  "  no  evidence  of  greater  male  variability,  but 
rather  of  a  slightly  greater  female  variability." 

He  finds,  for  example,  that  English  men  are  slightly  more 
variable  as  to  height  than  are  English  women  (4.07  : 4.03),  but 
that,  among  Germans,  women  are  considerably  more  variable 
than  men  (4.26:4.02),  as  they  are  also  among  the  French 
(4.35:3.88). 

In  the  long  bones  sometimes  one  is  more  variable,  sometimes 
the  other  ;  thus,  as  to  the  femur,  men  are  more  variable  :  Libyan 
(5.05:4.46),  French  (5.05:5.04),  Aino  (4.65:4.18),  and  Neo- 
lithic man  (4.73  :4-5i) ;  but  with  the  ancient  inhabitants  of  the 
Canary  Islands  the  reverse  is  true  (men,  4.64;  women,  4.71). 
In  all  cases  examined,  except  the  French  (men,  4.975  ;  women, 
5.365),  the  tibia  is  more  variable  in  men;  but  in  most  cases  the 
humerus  and  radius  are  more  variable  in  women. 

1  Pearson,  Chances  of  Death,  I,  256-377. 

2  Manifestly  the  coefficient  of  variability  is  the  only  correct  estimate  of  com- 
parative variability,  because  in  its  calculation  each  instance  is  compared  with  its 
own  type  as  a  base.    This  is  necessary,  because  the  stature  of  women,  for  example, 
is  different  from  that  of  men  ;  hence  the  two  cannot  be  compared  on  any  common 
basis.    This  is  the  only  way,  for  instance,  as  Pearson  points  out,  in  which  we  can 
compare  the  variability  of  man  with  that  of  the  elephant ;  in  any  other  way  the 
elephant  would  appear  more  variable,  because  he  is  bigger. 


572 


TRANSMISSION 


The  averages  of  coefficients  of  variability  for  all  "  long-bone  " 
determinations  are  as  follows  : l 


FEMUR 

TIBIA 

HUMERUS 

RADIUS 

Men 

4.82 

t.M 

4.88 

4.8l 

\Vomen 

4  & 

4.01 

C.IO 

c  10 

Though  these  are  human,  not  animal  data,  yet  they  involve 
skeletal  measurements  which  are  among  the  most  fundamental 
of  all  organic  parts,  and  they  scarcely  warrant  the  sweeping 
assertion  that  males  are  decidedly  more  variable  than  females. 
Pearson  is  entirely  justified  in  his  protest  against  what  he  calls 
this  "  pseudo-scientific  superstition"  and  the  sweeping  conclu- 
sions involving  "  social  and  practical  consequences  "  affecting 
"  the  whole  of  our  civilization."2 

In  body  weight,  both  among  English  (men,  10.37;  women, 
13.37)  and  among  Germans  (men,  20.67  '•>  women,  25.07),  women 
are  decidedly  more  variable  than  men.3 

In  weight  at  birth,  both  among  English  (boys,  15.65  ;  girls, 
14.44)  and  among  Germans  (boys,  13.567;  girls,  13.278),  the 
males  are  more  variable  ;  but  among  the  Belgians  the  reverse 
is  true  (boys,  14.66;  girls,  17.62). 

Data  of  this  sort  are  full,  but  unfortunately  confined  mostly 
to  humans.  From  all  sources  it  seems  that  men  are  more  vari- 
able in  "height  when  sitting"  and  in  "  swiftness  of  blow,"  but 
that  women  are  more  variable  in  "  stature  "  (height  when  stand- 
ing), "  span,"  "body  weight,"  "breathing  capacity,"  "strength 
of  pull,"  "squeeze  of  hand,"  and  "keenness  of  sight." 

As  Pearson  points  out,  some  of  these  variants  would  disappear 
if  women  were  subjected  to  the  same  conditions  of  life  as  are 
men,  and  we  need  to  be  cautious  when  applying  these  data  to 
races  in  general,  —  for  which  future  researches  are  sorely  needed. 
We  certainly  are  not  warranted  in  assuming  sweeping  and  funda- 
mental differences  in  variability  between  the  sexes.  Here  again 

1  Pearson,  Chances  of  Death,  I,  305.  a  Ibid.  I,  256  and  376. 

3  Incidentally,  the  same  data  warrant  our  conclusion  that  the  German  race, 
both  men  and  women,  are  more  variable  than  the  English  as  to  body  weight. 


PREPOTENCY 


573 


is  fertile  territory  for  careful  and  exhaustive  statistical  studies, 
which  alone  will  yield  reliable  results  on  which  principles  of 
selection  and  breeding  may  be  based. 

SECTION  III— INFLUENCE  OF  AGE  ON  PREPOTENCY 

Is  one  parent  prepotent  over  the  other  merely  by  reason  of 
age  ?  The  question  is  exceedingly  important,  but  the  writer  is 
not  aware  of  reliable  data  bearing  upon  the  subject.  The  matter 
could  be  determined  by  sufficient  investigation  into  the  offspring 
from  parents  with  some  considerable  discrepancy  as  to  age,  and 
by  comparing  the  coefficients  of  heredity  between  the  offspring 
of  young  and  those  of  old  parents,  not  only  with  each  other  but 
with  the  normal  of  the  race.  Helpful  as  it  would  be  to  know  the 
facts  upon  this  point,  they  have  not  yet  been  discovered  and  it  is 
idle  to  speculate.  We  have  no  choice  but  to  wait  until  the  research 
is  made  in  what  will  one  day  constitute  a  prolific  field  for  study. 

SECTION   IV  — INFLUENCE  OF    CONSTITUTIONAL   VIGOR 
UPON  PREPOTENCY 

This  is  an  important  question,  upon  which  we  lack  reliable 
information.  Common  sense  seems  to  indicate  that  the  more 
weakly  parent  would  not  be  equally  influential  in  impressing  his 
or  her  characteristics,  but  we  cannot  yet  say  to  what  extent  the 
character  of  the  reproductive  cells  is  dependent  on  vigor.  Here 
again  speculation  can  easily  run  riot ;  but  from  the  fact  that, 
for  other  reasons,  we  should  reject  the  non-vigorous  parent,  the 
question  loses  most  of  its  point  except  in  human  affairs,  which 
do  not  concern  us  here. 

That  one  stalk  in  a  hill  of  corn  often  resists  the  effects  of 
frost  when  neighboring  stalks  are  killed  is  a  fact  that  has  long 
been  noted,  but  whether  such  plants  are  prepotent  in  transmit- 
ting resistance  to  frost  is  not  known.  It  is  a  significant  fact, 
however,  that  Dr.  Hopkins,  of  the  University  of  Illinois,  when 
conducting  experiments  with  soils  containing  an  excess  of  mag- 
nesium, noticed  one  year  a  single  wheat  plant  that  flourished 
well  where  all  others  succumbed.  Saving  seed  from  this  plant, 


574  TRANSMISSION 

he  found  its  descendants  highly  resistant,  flourishing  well  where 
ordinary  wheat  totally  failed.  It  was,  apparently,  a  true  mutant, 
with  extra  strong  resistance  to  magnesium. 

Influence  of  development  upon  prepotency.  Many  biologists 
contend  that  transmission  depends  to  a  large  extent  upon  the 
development  of  the  parent ;  that  a  stallion  trotting  bred,  for  ex- 
ample, would  get  speed  much  more  successfully  if  he  himself 
were  "  developed  "  or  "  worked  "  upon  the  track  than  would  the 
same  stallion  kept  equally  healthful  and  vigorous  but  not  devel- 
oped as  to  actual  speed.  A  natural  conclusion  of  this  contention 
is,  of  course,  that  the  same  sire  will  get  more  speed  in  his  middle 
and  later  years  than  would  be  possible  before  he  was  developed. 

This  is  the  very  point  of  Casper  L.  Redfield's  recent  articles1 
setting  forth  what  he  calls  his  "  dynamic  theory  of  heredity." 
He  brings  many  instances  and  much  argument  in  support  of  the 
assumption,  but  in  the  opinion  of  the  writer  the  method  of  proof 
adopted  is  not  competent  to  settle  the  question,  nor  is  any 
method  able  to  do  so  that  is  based  upon  the  simple  enumeration 
of  instances. 

As  with  any  other  question  involving  great  variability,  the 
only  way  we  can  settle  this  is  by  employing  large  numbers  on 
both  sides  of  the  proposition ;  in  other  words,  by  comparing  the 
speed  of  all  the  horses  gotten  by  performing  sires  late  in  life 
with  the  records  of  the  get  of  the  same  sires  before  development, 
or  at  least  before  long  service  on  the  track.  Even  then  we  must 
learn  what  deductions  to  make,  if  any,  on  account  of  differences 
in  age ;  after  which,  we  may  hope  to  learn  the  real  effect  of 
development  upon  prepotency. 

As  the  matter  stands  now,  the/^r/  of  prepotency  is  patent  to 
both  the  casual  observer  and  to  the  careful  student ;  but  the 
reasons  for  this  difference  in  breeding  powers  are  not  yet  at  all 
well  understood.  Here,  as  in  many  other  directions,  we  await 
future  studies. 

Summary.  Individuals  of  the  same  ancestry  differ  marvel- 
ously  in  their  breeding  powers.  Some  can  produce  excellence 
directly  in  their  own  descendants,  and  others  indirectly  through 

1  See  The  Horseman,  XXV,  Nos.  19-41,  on  "  Breeding  the  Trotter"  ;  also  The 
American  Field,  LXII,  No.  25,  and  LXIII,  No.  9,  on  "Evolution  of  the  Setter." 


PREPOTENCY  575 

sires  and  dams  they  are  able  to  get.  The  line  of  descent  runs 
only  through  the  few  that  can  produce  breeders  of  breeders,  not 
simply  performers. 

Individual  excellence  is  not  a  certain  guide  to  breeding  powers, 
and  many  ordinary  individuals  are  among  the  greatest  breeders. 
This  is  neither  a  mystery  nor  a  fault  in  heredity ;  it  arises  from 
the  fact  that  individual  excellence  is  partly  a  matter  of  individual 
development  and  not  a  sure  index  of  real  ancestral  possessions. 
The  specimen  may  be  only  fairly  well  born,  though  faultlessly 
developed,  — in  which  case  he  will  probably  be  a  disappointment 
as  a  breeder ;  or  he  may  be  excellently  born,  but  only  fairly  well 
developed,  —  in  which  case  he  will  breed  "  better  than  he  is  him- 
self "  ;  still  again,  he  may  be  well  born  and  perfectly  developed, 
which  is  best  of  all. 

All  studies  yet  made  show  that,  on  the  average,  performers 
(those  individuals  possessing  high  individual  merit)  are  better 
breeders  than  non-performers ;  that  is,  than  those  which  do  not 
show  in  their  personal  development  a  high  degree  of  excellence, 
though,  as  we  should  at  once  surmise,  there  are  numerous  ex- 
ceptions, largely  arising  from  our  inability  to  accurately  judge 
individuals  by  external  appearances. 

SPECIAL  EXERCISES 

Work  out  special  cases  of  prepotency  in  the  breeding  and  speed  records 
of  trotting  and  running  horses,  in  the  advanced  registry  of  cows,  and  in  the 
famous  families  of  beef  cattle  and  of  swine.  Pay  special  attention  to  rela- 
tive prepotency  of  own  brothers  and  to  the  correlation  between  individual 
performance  and  breeding  powers. 

ADDITIONAL  REFERENCES 

A  MEASURE  OF  INTENSITY  OF  TRANSMISSION.    By  Francis  Galton,  1899. 

Nature,  LX,  29. 
DISTRIBUTION  OF  PREPOTENCY.    (Trotting-horse  records.)    By  Francis 

Galton.    Nature,  LVIII,  246-247. 
INFLUENCE    OF    SEX   ON    SIZE    OF    OFFSPRING.    By  F.    B.   Mumford. 

Experiment  Station  Record,  XV,  542. 
PREPOTENCY  AND  XENIA.    By  C.  Correns.   Experiment  Station  Record, 

XI,  1016. 
PREPOTENCY  OF  DIFFERENT  PLANTS.    By  W.  W.  Tracy.    Experiment 

Station  Record,  XIII,  324. 


PART   IV  —  PRACTICAL   PROBLEMS 


CHAPTER  XVI 

SELECTION 

We  have  just  seen  the  power  of  selection  to  fix  type,  providing 
it  continue  unchanged  for  five  or  six  generations.  By  this  we 
discover  that  selection  is  the  most  direct  and  powerful  means  of 
improvement  at  the  disposal  of  the  breeder;  indeed,  it  would 
not  be  too  much  to  say  that  it  is  the  only  means  of  permanent 
improvement  that  is  under  his  direct  control. 

In  most  phases  of  the  breeding  problem  the  stockman  or  the 
plant  improver  is  an  on-looker  merely ;  but  in  the  matter  of 
selection  he  becomes  an  active  agent,  and  his  decisions  and  his 
acts  are  powerful  either  for  good  or  evil  in  controlling  the  des- 
tinies of  the  breed  or  the  variety  he  handles. 

In  this,  to  a  very  large  extent,  he  supplants  natural  selection, 
and  if  he  is  to  succeed  he  must  be  well  grounded  in  four  funda- 
mentals when  he  thus  takes  a  hand  in  the  course  of  nature : 

1.  He  must  have  a  clear  idea  of  what  he  desires  to  accomplish, 
and  he  must  adhere  persistently  to  one  standard. 

2.  He  must  be  well  informed  as  to  the  history  of  the  breed 
or  the  variety  he  handles  and  of  the  variations,  both  new  and 
old,  which  it  is  likely  to  afford. 

3.  He  must  know  the  general  principles  involved  in  selection 
in  order  to  know  the  forces  with  which  he  deals  and  what  is 
likely  to  happen  when  he  interferes. 

4.  He  must  have  judgment  as  to  when  and  how  far  he  may 
depart  from  sound  practice  on  account  of  economic  or  other 
considerations. 

When  we  reach  this  phase  of  breeding  operations  we  begin  to 
touch  financial  as  well  as  biological  principles,  and  all  this  must 

577 


578  PRACTICAL   PROBLEMS 

be  done  with  reference  both  to  what  is  desirable  and  to  what 
will  pay ;  hence  the  necessity  of  considering  all  phases  of  the 
selection  problem  from  a  double  standpoint.  Each  consideration 
outlined  is  self-evident,  yet  each  is  of  sufficient  importance  to 
merit  further  consideration. 


SECTION  I  — IDEALS  IN  SELECTION 

Among  the  multitude  of  variations  which  every  breed  and 
every  variety  will  present,  the  breeder  must  know  which  are 
useful.  The  great  mass  must  be  discarded,  from  the  mere  point 
of  numbers,  and  no  one  cause  of  failure  is  more  common  than 
a  vacillating  policy  regarding  standards  of  selection. 

This  uncertainty  is  due  to  no  other  fact  than  that  the  breeder 
does  not  know  quite  what  he  wants.  He  is  "  in  the  market  " 
for  "any  good  thing"  that  may  turn  up.  In  the  course  of  his 
breeding  operations  a  great  many  new  and  more  or  less  promis- 
ing things  will  appear.  Unless  he  has  unlimited  means  and 
boundless  space  for  his  operations,  these  must  be  discarded 
with  seeming  ruthlessness,  or  he  will  speedily  have  an  assort- 
ment of  novelties  which  if  bred  among  themselves  will  overrun 
his  premises,  and  if  bred  into  his  permanent  stock  will  produce 
a  veritable  jumble,  out  of  which  no  good  thing  can  come.  In 
this  way  ancestry  and  pedigree  can  become  so  hopelessly  mixed 
as  to  be  worthless.  This  may  happen  with  any  breed,  and  even 
within  the  limits  of  purity  of  blood ;  indeed  it  has  happened 
over  and  over  again,  in  all  breeds,  through  the  misguided  enthu- 
siasm of  breeders  working  without  well-defined  standards. 

Standards  wisely  fixed.  Standards  must  not  be  left  to  chance. 
They  must  not  be  warped  or  altered  by  novelties,  no  matter  how 
curious  or  attractive.  They  must  be  fixed  in  advance,  like  build- 
ing plans  and  specifications,  and  should  be  fixed  in  the  light  of 
what  is  needed  and  what  the  breed  is  likely  to  afford.  Indeed, 
the  standards  should  be  roughly  fixed  before  the  breed  is  chosen. 

Once  chosen,  standards  should  be  preserved  unchanged.  As 
the  artist  sees  his  picture  before  he  mixes  his  colors,  and  as  the 
sculptor  chips  away  at  his  marble  to  bring  out  the  particular 
figure  that  stands  in  his  mind,  undisturbed  and  undissuaded 


SELECTION 


579 


from  his  purpose  by  the  many  other  excellent  figures  that  might 
be  cut  from  the  same  material,  so  the  breeder  should  adhere  to 
his  standards  doggedly.  They  should  be  wisely  chosen,  it  is 
true,  but,  once  sure  of  that  fact,  and  with  the  law  of  ancestral 
heredity  in  mind,  nothing  should  warp  the  judgment  as  to  change. 
Everything  that  helps  to  secure  the  ideal  should  be  accepted, 
and  everything  else,  no  matter  how  attractive  in  itself,  should 
be  pushed  aside,  —  unless,  indeed,  the  breeder  have  unlimited 
means  and  is  minded  to  do  not  one  thing  but  many  things. 

Keep  blood  lines  pure.  But  if  the  breeder  is  minded  to  indulge 
in  experiments  outside  the  chosen  standard,  these  experiments 
must  be  carried  on  separately.  Blood  lines  must  be  kept  pure, 
not  pure  within  breed  lines  simply,  but,  remembering  the  law  of 
ancestral  heredity  and  the  pull  of  the  ancestors  back  of  the 
immediate  parent,  they  should  be  kept  as  pure  as  selection  can 
make  them. 

Objects  of  selection.  Indeed,  while  one  object  of  selection  is 
to  reduce  numbers,  by  far  the  larger  object  is  to  purify  the 
ancestry,  to  the  end  that  inheritance  from  all  the  ancestors  shall 
be  alike,  so  that  the  "  pull  of  the  race"  shall  not  be  different 
from  the  transmission  of  the  immediate  parent.  This  being  so, 
selection  according  to  vacillating  standards  is  no  selection  at  all, 
and  he  who  returns  from  each  state  fair  or  exposition  with  new 
rather  than  improved  standards  cannot  hope  to  meet  the  highest 
success  as  a  breeder  or  contribute  real  excellence  to  the  breed 
he  has  chosen. 

SECTION   II  —  HISTORICAL  KNOWLEDGE  OF  THE  BREED 

NECESSARY 

This  is  almost  self-evident,  and  yet  the  number  of  breeders 
who  do  not  possess  it,  and  the  readiness  with  which  large  money 
is  invested  and  plans  made  which  will  require  a  lifetime  to  carry 
out,  —  all  with  the  most  meager  knowledge  of  the  breed  that 
is  chosen,  —  show  how  lightly  this  matter  rests  in  the  minds  of 
many  otherwise  intelligent  and  cautious  business  men. 

These  men  proceed  as  if  the  material  they  were  to  work  with 
were  new  material,  ready  to  be  molded  for  the  first  time  into 


580  PRACTICAL   PROBLEMS 

any  desired  form,  while  in  truth  it  is  very  old  material,  with 
which  many  men  have  worked  before,  —  sometimes  for  profit, 
often  for  amusement  merely. 

And  the  breed  has  inherited  the  results  of  all  these  experi- 
ments, both  bad  and  good,  so  that  this  material  is  in  some 
respects  the  better  and  in  some  the  worse  for  what  others  have 
tried  to  do  with  it.  The  most  ordinary  business  sense  and  the 
commonest  biological  principles  indicate  that  before  the  breeder 
begins  serious  operations  he  should  know  all  that  can  be  known 
of  the  breed  or  the  variety  he  proposes  to  work  with.  In  no 
other  way  can  he  make  intelligent  selection. 

A  few  crude  examples  will  suffice  to  illustrate.  Many  breeders 
of  English  strains  of  cattle  will  not  only  destroy  a  white  calf, 
but  will  consider  its  appearance  an  evidence  of  impurity  of  blood, 
not  knowing  that  these  breeds  in  general  have  descended  from 
the  wild  white  cattle  of  Great  Britain.  It  is  only  recently  that 
white  has  been  restored  to  favor  as  a  good  Shorthorn  color. 

The  Berkshire  swine  are  the  result  of  a  cross  of  the  large 
English  hog  with  the  small,  thin-haired,  plum-colored  Neapolitan, 
and  more  than  one  Berkshire  herd  has  been  ruined  by  selecting 
for  breeding  purposes  the  plump,  quick-maturing,  fine-haired, 
and  most  attractive  pigs. 

A  famous  breeder  of  Kentucky  was  remarkably  successful 
with  Shorthorns,  yet  in  his  efforts  to  secure  a  high  head  and  a  low 
brisket  he  forgot  the  natural  wild  type,  and  speedily  his  breeding 
came  to  be  known  by  its  sloping  rump  and  "  split  quarters." 

The  breeder  should  know  the  peculiarities  of  his  blood.  The 
first  information  needed  by  the  prospective  breeder  is  a  good 
knowledge  of  the  inherent  faults  of  the  breed.  He  needs  to 
know,  for  example,  that  the  Berkshires  are  naturally  deficient  in 
the  hams,  and  the  Poland-Chinas  in  the  shoulders ;  that  the 
Duroc  Jerseys  are  uneven  in  type,  and  the  Chester  Whites  a 
bit  coarse  in  the  bone.  He  needs  to  realize  that  the  Jersey  is 
sometimes  extremely  delicate ;  that  many  of  the  Holstein-Frie- 
sians  are  rough,  and  that  the  breed  is  preeminently  short-tailed, 
—  hence  the  provision  in  the  scale  of  points  that  the  bone  of 
the  tail  should  reach  the  hock,  which  was  but  rarely  the  case  in 
the  foundation  stock  of  the  breed. 


SELECTION  .  581 

The  breeder  of  Shorthorns  should  know  in  advance  that  it  is 
a  breed  not  of  one  type,  but  of  many  types,  of  varying  degrees 
of  excellence.  He  who  expects  to  breed  Herefords  should  know 
at  once  that  the  breed  is  one  of  two  types,  so  distinct  as  to  be 
almost  dimorphic.  The  Angus  breeder  should  not  be  surprised 
at  some  failures,  or  at  a  red  specimen,  nor  the  Galloway  breeder 
at  considerable  roughness,  or  at  the  occasional  appearance,  with- 
out warning,  of  more  or  less  white. 

Breeders  of  the  Percheron  should  know  that,  of  all  modern 
breeds,  this  retains  the  most  of  the  Arabian  infusion  due  to  the 
crusades,  and  that  until  recently  he  was  a  small  not  a  heavy 
horse,  hence  his  "  bone  "  is  to  be  carefully  looked  after. 

These  and  a  mass  of  other  breed  peculiarities,  both  good  and 
bad,  should  be  fully  in  the  mind  of  the  breeder.  Of  course  most 
of  the  advocates  of  any  breed  will  stoutly  resent  the  slightest 
implication  of  faults  in  their  favorites,  yet  the  fact  remains  that 
the  really  able  and  successful  breeders  know  very  well  that  they 
must  be  constantly  upon  their  guard  against  certain  happenings 
which  may  be  called  "  faults  "  or  "  peculiarities  "  according  to 
the  definition  of  terms. 

SECTION  III  — GENERAL  PRINCIPLES  INVOLVED  IN 
SELECTION 

When  the  breeder  determines  which  individuals  shall  and 
which  shall  not  reproduce,  he  must  do  it  with  all  the  intelligence 
possible,  and  with  a  full  knowledge  of  all  that  is  involved  in  his 
decision,  which  is  most  far-reaching  and  irrevocable  in  its  con- 
sequences. It  is  the  purpose  here  to  outline  some  of  the  prin- 
cipal considerations  that  should  be  in  mind  when  these  decisions 
are  made. 

The  purpose  of  selection.  Primarily  the  purpose  of  selection 
is  to  reduce  numbers,  or  to  influence  type  (whichever  way  we 
please  to  put  it),  but  in  the  last  analysis  it  is  to  prevent  the 
birth  of  unwelcome  individuals  not  suited  to  the  purposes  of 
man  ;  and  by  as  much  as  the  breeder  is  able  to  forecast  off- 
spring, by  so  much  is  he  able  to  surround  himself  with  good  and 
serviceable  individuals  without  resorting  to  wholesale  slaughter 


582  PRACTICAL  PROBLEMS 

after  birth,  with  its  attendant  losses.  In  all  theory  we  would 
prevent  the  birth  of  unprofitable  individuals,  and  we  succeed 
nearly  in  proportion  as  we  are  skillful  in  selection. 

Selection  results  in  absolute  increase  in  quality,  not  merely  in 
an  elevation  of  the  average  by  eliminating  the  lower  values. 
We  have  been  told  that  selection  results  only  in  raising  the 
average  by  cutting  off  the  lower  values,  but  that  the  upper 
values  are  not  influenced  thereby.  This  is  clearly  an  error,  as 
will  be  seen  by  a  reference  to  any  systematic  breeding  experi- 
ments and  especially  to  the  tables  giving  the  results  of  selecting 
corn  for  high  or  low  protein  or  high  or  low  oil.1  Here  it  is  seen 
that,  in  the  progress  of  selection,  by  the  use  of  successively 
increasing  standards,  new  and  JiigJicr  values  constantly  appeared. 
Not  only  that,  but  the  principle  is  still  operative  after  ten  years 
of  selection,  and  the  coefficient  of  variability  is  not,  in  most  cases, 
growing  less?  In  general  it  may  be  said  that  the  result  of 
systematic  selection  is  to  shift  the  type  but  not  greatly  to 
reduce  variability,  and  when  applied  to  a  number  of  characters 
at  the  same  time  it  very  clearly  and  very  rapidly  defines  the 
type  of  the  strain  or  breed. 

In  breeding  the  beet  for  sugar,  the  cow  for  milk,  the  horse 
for  speed,  or  any  animal  or  plant  for  any  definite  quality,  there 
is  every  reason  for  believing  that  we  have  succeeded  in  pro- 
ducing a  higher  order  of  excellence  than  ever  arose  spontaneously 
in  the  race  while  in  a  state  of  nature ;  that  is  to  say,  we  have 
done  more  than  to  raise  the  average,  we  have  elevated  the 
upper  limits. 

The  upper  limits  of  improvement.  Manifestly  this  increase  of 
quality  cannot  go  on  indefinitely.  We  cannot  breed  the  horse 
to  be  as  large  as  the  elephant ;  or,  if  we  could,  there  will  be  an 
upper  limit  somewhere.  What  will  set  these  limits  is  an  interest- 
ing question.  In  some  cases,  no  doubt,  the  limit  would  be  fixed 
by  purely  mechanical  principles,3  in  others  by  physiological 
restrictions,  such  as  the  size  of  the  heart  and  the  labor  of 

1  See  pages  494  and  496. 

2  Ibid. 

8  For  example,  there  is  a  mechanical  limit  to  the  length  of  leg,  or  to  the  sixe 
of  udder. 


SELECTION  583 

circulating  the  blood ;  but  apparently  we  have  not  yet,  in  any 
line,  approached  a  limit  so  high  that  variation  is  not  abundantly 
able  to  present  still  higher  values.  How  long  this  may  go  on  is 
a  question  both  of  scientific  and  of  utilitarian  interest,  but  it  will 
be  remembered  that  variation  is  supposed  not  to  be  reducible 
below  some  85  or  89  per  cent  of  its  original  amount.1 

Selection  for  definite  purposes  often  against  valuable  qualities, 
especially  fertility,2  vigor,  and  longevity.  So  intent  are  we  upon 
securing  some  coveted  character,  as  early  maturity,  size,  milking 
or  feeding  quality,  that  we  overlook  other  less  visible  but  none 
the  less  essential  qualities.  This  is  best  seen  among  our  meat- 
producing  animals.  For  example,  it  is  the  heavy-fleshed,  early- 
maturing  sow  pig  that  finds  her  way  to  the  prize  ring  and  ulti- 
mately to  the  fashionable  breeding  pen.  Now  this  is  not  the 
most  prolific  type  of  swine,  and  under  this  policy  of  selection, 
primarily  for  flesh  and  fat,  it  is  not  surprising  that,  of  all  our 
animals,  those  bred  for  meat  production  are  lowest  in  fertility. 
We  know  of  no  fundamental  reason  why  it  must  be  so  ;  it  simply 
is  so  because  fertility  has  been  so  generally  neglected  in  the 
exclusive  standards  and  methods  of  selection  employed. 

"  Fertility,"  "  vigor,"  and  "longevity"  are  all  relative  terms. 
All  animals  and  plants  have  some  degree  of  vigor,  and  nearly 
all  are  able  to  reproduce,  at  least  to  some  extent.  The  evils  on 
this  score  arise  not  from  the  non-breeder,  or  the  individual  that 
succumbs  in  early  life,  but  from  those  individuals  which,  though 
not  entirely  wanting,  are  yet  deficient  in  those  fundamental 
qualities  that  are  of  necessity  correlated  with  propagation  of  a 
vigorous,  lasting,  and  prosperous  race.  It  is  the  "  shy  breeder" 
that  comes  to  nothing,  and  that  is  the  root  of  many  of  the  evils 
of  the  breeding  herd. 

The  relative  values  of  prolific  and  of  shy  breeders  may  be 
brought  out  by  comparing  three  cows,  for  example,  one  of  which 
will  produce  two  calves  before  she  stops  breeding,  another  four, 
and  another  six.  After  five  generations  the  fertile  female 
descendants  of  each  would  be  as  follows,  assuming  that  one  half 

1  Pearson,  Grammar  of  Science,  p.  483. 

2  The  word  "  fertility  "  is  used  in  preference  to  "  fecundity  "  because  the  latter 
term  refers  especially  to  females. 


PRACTICAL  PROBLEMS 


the  calves  are  males  and  one  half  females,  and  that  all  descendants 
are  prolific  in  the  same  proportion  as  the  originals. 

NUMBER  OF   LIVING  AND  PRODUCING  FEMALES  AT  THE   END   OF 

VARIOUS  GENERATIONS,  FROM  Cows  OF  DIFFERENT 

DEGREES  OF  FERTILITY 


FEMALES 

Cow  No. 

CALVES 

First 

Second 

Third 

Fourth 

Fifth 

Generation 

Generation 

Generation 

Generation 

Generation 

r 

2 

I 

I 

I 

, 

I 

2 

4 

2 

4 

8 

16 

32 

3 

6 

3 

9 

27 

81 

243 

It  is  easy  to  see  that  no  matter  what  the  individual  excellence 
of  cow  No.  i  and  her  descendants,  they  could  never  build  up  a 
herd.  Their  rate  of  reproduction  is  so  low  as  only  to  keep  good 
the  original  number.  Careful  search  will  discover  a  surprising 
number  of  females  of  this  class  in  the  herds  of  otherwise  suc- 
cessful stockmen,  —  useless  from  any  standpoint  except  the 
show  ring. 

On  the  other  hand,  cow  No.  2  and  her  descendants  produce 
at  a  rate  that  will  not  only  keep  their  numbers  good  but  will 
admit  of  selection,  and  this  is  the  case  to  a  greater  extent  with 
No.  3,  whose  descendants  in  the  fifth  generation  would  be  no 
fewer  than  243  as  compared  with  32  for  No.  2  and  i  for  No.  i. 
It  is  easy  to  see  that  one  such  cow  as  No.  3  in  a  herd  of  20 
like  No.  i  would  in  a  few  years,  by  very  breeding  powers, 
dominate  the  herd,  at  the  same  time  affording  generous  num- 
bers for  selection,  whereas  the  descendants  of  No.  i  would 
afford  no  opportunity  whatever  for  selection.  It  is  clear  to  the 
most  casual  student  that  when  our  standards  are  decidedly 
against  the  highest  fertility  they  are  dangerous,  if  not  fatal,  to 
the  race. 

Need  of  comparatively  large  numbers  in  breeding  operations. 
Obviously,  comparatively  large  numbers  are  necessary  in  order  to 
provide  selection  with  material  sufficient  for  securing  uniformity 


SELECTION  585 

in  type.  Enthusiastic  amateurs  have  often  attempted  to  maintain 
a  "  small  herd  of  exceptional  excellence."  Such  attempts  have 
always  failed,  and  must  fail,  for  the  reason  that  such  a  herd 
affords  too  little  material  for  selection,  and  therefore  the  impos- 
sibility of  maintaining  its  type  is  a  bar  not  only  to  progress,  but 
even  to  the  bare  maintenance  of  the  initial  excellence.  Suppose, 
for  example,  that  a  small  herd  of  exceptional  animals  be  brought 
together,  —  say,  three  cows  and  a  bull,  the  choice  from  many 
of  the  best  herds.  What  are  the  mathematical  probabilities  of 
their  being  able  to  reproduce  their  own  number  of  equal  excel- 
lence before  the  original  herd  disappears  ?  It  is  very  slight 
indeed,  unless  one  of  the  number  proves  to  be  a  phenomenal 
individual  breeder,  which,  in  truth,  occasionally  happens. 

Value  of  the  exceptional  breeder.  The  more  the  matter  is 
studied  the  more  it  will  be  found  that  the  excellence  of  any  herd 
or  of  any  breed  is  sustained  and  advanced,  not  by  the  general 
mass,  but  by  a  few  exceptional,  not  to  say  phenomenal,  breeders. 

The  trotting  blood  of  to-day  owes  its  high  development  to  a 
very  few  foundation  animals,  coming  to  us  through  Hamble- 
tonian  10,  and  sustained  and  developed  by  an  insignificantly 
small  percentage  of  the  general  mass  of  stallions.'1 

The  excellence  of  the  Shorthorn  is  maintained  in  the  same 
way,  and  it  is  not  too  much  to  say  that  in  all  probability  there 
are  never  living  at  any  one  time  in  any  breed  more  than  a  score 
or  so  of  animals  that  produce  anything  like  a  real  and  positive 
advance  in  the  breed,2 —  "  The  line  of  descent  runs  not  through 
their  veins." 

The  exceptional  breeder  not  necessarily  the  exceptional  indi- 
vidual. Neither  Hambletonian  10  nor  Geo.  Wilkes  was  the 
best  trotter  in  the  breed ;  indeed,  the  highest  performers  have 
contributed  little.  They  were  the  offputs,  but  accidentally,  or 
of  necessity,  they  were  not  of  the  main  line  of  descent.  In  the 
corn-breeding  experiments  already  cited,  the  ear  to  which  the 
present  high-protein  stock  all  traces  was  not  one  of  the  originally 
highest  protein  ears.  The  great  sires  and  the  great  dams  that 

1  See  chapter  on  "  Heredity,"  table  of  the  Big  Ten,  p.  555. 

2  This  number  is  too  high.    The  Shorthorn  breed  probably  never  saw  twenty 
such  bulls  as  Champion  of  England. 


586  PRACTICAL  PROBLEMS 

have  contributed  most  to  their  breeds  have  often  been  incon- 
spicuous as  individuals  and,  unfortunately,  often  have  been  dead 
long  before  their  real  service  to  the  breed  was  known  and 
recognized. 

Need  of  the  actual  breeding  test.  So  valuable  is  the  excep- 
tional breeder,  and  so  impossible  is  it  to  know  him  (or  her)  in 
advance  by  the  ordinary  methods  of  judgment,  that  only  the 
actual  breeding  test  is  reliable.  The  only  safe  method  is  to 
select  the  herd  of  females  of  high  fertility  and  uniformly  excel- 
lent breeding  record,  and  then,  knowing  the  female  side  by  long 
and  intimate  experience,1  select  the  sire  for  his  performance 
record  in  getting  young. 

The  tests  should  first  be  made  with  a  few  well-known,  and 
therefore  fairly  aged,  females.  Too  much  cannot  be  said  against 
the  practice  of  putting  a  new  young  sire  at  once  into  full  service 
in  the  herd,  no  matter  what  his  individuality  or  his  pedigree. 
However  promising,  he  must  be  subjected  to  the  actual  test, 
and  after  having  proved  his  breeding  powers  with  known  females 
he  should  be  used  to  the  utmost  as  long  as  he  will  breed  success- 
fully, and  not  discarded  because  of  loss  of  bloom,  decline  in 
form,  or  even  for  the  acquirement  of  an  evil  disposition.  It  is 
from  the  proved  patriarchs  and  from  the  grandmothers  of  the 
herd  that  real  excellence  will  come,  and  the  real-  value  of  proved 
breeders,  male  or  female,  is  beyond  computation.2 

Install  the  successor  early.  It  is  never  too  early  to  seek  a  new 
head  to  an  established  herd.  Proved  sires  are  seldom  for  sale, 
and  the  only  recourse  for  the  breeder  is  to  prove  his  own ; 
indeed,  what  he  needs  is  a  sire  that  will  produce  well  with  his 
females. 

It  takes  much  time  and  often  many  trials  to  find  a  worthy 
successor  to  the  head  of  the  herd.  Putting  it  off  too  long,  and 
a  feeling  of  fancied  security,  are  the  two  causes  of  leaving  a 

1  A  complete  breeding  record  should  be  kept  of  each  female  separately.    See 
chapter  on  "  Animal  Breeding." 

2  The  author  has  a  mass  of  data  collected  from  hundreds  of  breeders,  from 
which  it  appears  that  young  bulls  are  commonly  preferred  because  they  are  cheaper, 
because  their  period  of  service  is  longer,  and  because  they  are  more  manageable. 
It  appears  too  that  when  a  "  test  "  is  made  it  is  commonly  not  upon  old  and  known 
cows,  but  upon  heifers. 


SELECTION  587 

herd  without  a  head,  and  of  the  enforced  evil  practice  of  using 
an  untried  sire. 

Comparative  value  of  male  and  female.  In  the  matter  of  pre- 
potency, as  we  have  already  seen,  neither  parent  has  any  partic- 
ular advantage  over  the  other.  But  this  refers  to  a  single 
offspring,  and  is  only  a  part  of  the  question.  The  real  differ- 
ence is  one  of  numbers.  Among  animals  the  sire  may  produce 
perhaps  a  hundred  in  a  season,  while  the  dam  is  limited  to  one 
individual  or  at  most  (among  hogs)  to  two  litters.  The  trotting 
records  show  that  certain  sires  produced  hundreds  of  offspring 
in  the  list,  but  Green  -Mountain  Maid,  who  produced  nine  living 
foals,  long  held  the  record,  since  greatly  exceeded  by  other  mares. 

For  purely  mathematical  reasons,  therefore,  the  female  is  of 
vastly  less  consequence  in  herd  or  breed  improvement,  —  indeed, 
wherever  polygamous  mating  occurs.  It  is  here  a  question  of 
numbers  and  opportunity.  As  regards  these,  the  upper  limit  of 
the  male  is  very  high  and  of  the  female  very  low,  which  fact 
teaches  the  necessity  of  extreme  care  in  the  selection  of  the 
sire,  not  so  much  for  biological  as  for  numerical  reasons.  The 
single  female  is,  therefore,  comparatively  insignificant.  Unless 
she  be  one  of  the  few  phenomenal  breeders  her  individual  power 
for  good  is  exceedingly  low,  and  the  readiness  of  many  buyers 
to  pay  extreme  prices  for  females,  especially  of  cattle,  is  wholly 
unaccountable. 

The  sire  more  than  half  the  herd.  It  has  become  a  proverb 
that  the  sire  is  half  the  herd.  He  is  far  more  than  that.  He 
is  half  of  the  first  generation,  three  quarters  of  the  next,  seven 
eighths  of  the  third,  and  so  on  until,  if  judicious  selection  be  main- 
tained for  a  fezv  generations,  the  cJiaracter  of  the  Jierd  -will  be 
fixed  by  the  sire  alone.  This  being  true,  the  folly  of  maintaining 
a  sire  with  but  two  or  three  high-class  females  is  evident ;  he 
should  have  larger  opportunity.  All  this  means  that,  as  a  begin- 
ning, numbers  are  of  more  consequence  relatively  than  quality 
on  the  side  of  the  dam,  and  that  if  the  breeder  must  choose 
between  the  two  it  is  better  to  put  a  given  amount  of  money 
into  a  good  number  of  plain  females  than  into  a  smaller  number 
of  high  quality,  but  that  in  all  cases  the  sire  should  have  quality 
and  plenty  of  it,  because  of  the  principle  here  stated. 


588  PRACTICAL  PROBLEMS 

Size  in  the  dam ;  quality  in  the  sire.  In  many  lines  of  breed- 
ing, size  in  the  sire  is  considered  by  many  breeders  as  of  first 
importance.  This  is  against  reason  and  biological  principles. 
We  need  in  the  sire  all  the  desirable  characters  possible,  and 
these  are  most  readily  found  in  animals  of  medium,  not  extreme, 
size.  It  is  comparatively  easy  to  get  size  alone,  and  this  can  be 
gotten  on  the  side  of  the  dam.  The  herd  must  depend  for  uni- 
formity largely  upon  the  sire,  and  he  should  be  freed  as  much 
as  possible  from  the  requirement  of  size.1 

Natural  selection  always  at  work.  Natural  selection  is  always 
at  work  in  field  and  flock  and  herd.  Of  this  we  may  be  well 
assured.  No  matter  what  we  desire  to  accomplish,  our  success 
or  our  failure  will  turn,  in  the  last  analysis,  upon  the  fitness  of 
the  product  to  live  and  to  reproduce  amid  the  conditions  by 
which  it  must  be  surrounded. 

Some  of  the  best  things  among  both  plants  and  animals  are 
weak  or  comparatively  unprolific.  Natural  selection  is  decidedly 
against  their  survival,  no  matter  how  valuable  they  may  be  to 
us.  Lack  of  constitution  or  vigor  is  easily  seen,  but  lack  of 
breeding  powers  is  not  so  easily  detected,  and  here  is  where 
the  greatest  amount  of  trouble  arises. 

We  have  already  seen  that  in  nature  the  population  that  is 
born  into  the  world  is  proportioned  according  to  relative  fertility, 
while  the  population  that  is  permitted  to  remain  is  conditioned 
upon  relative  powers  to  resist  adverse  conditions  and  to  fit  into 
the  conditions  of  life. 

This  same  relation  obtains  in  our  herds,  with  this  difference, 
that  we,  with  our  selection,  decide  arbitrarily  what  shall  live. 
That  is  right  and  according  to  economic  necessity,  —  only  in 
doing  so  we  must  not  assume  that  all  individuals  and  types  are 
equally  fertile  and  equally  able  to  propagate  themselves. 

It  may  be  in  certain  instances  that  in  order  to  secure  what 
we  desire  we  shall  of  necessity  proceed  temporarily  with  some 

1  A  manifest  exception  to  this  general  principle  is  in  the  breeding  of  draft 
horses  from  farm  mares.  Here  size  is  an  objection  on  the  dam's  side,  besides 
being  difficult  to  get.  Weight  is  the  chief  desideratum  just  now  (it  will  not  always 
be  so)  in  draft-horse  breeding,  and  \a\\Aev  present  circumstances  it  must  be  sought 
especially  in  the  sire. 


SELECTION  589 

handicap  as  to  fertility,  and  perhaps  as  to  vigor,  in  which  case 
these  two  essential  qualities  must  be  borne  in  mind  and  the 
deficiency  remedied  in  future  selections.  The  breeder  is  never 
to  forget  that  natural  selection  is  at  work  side  by  side,  or  per- 
haps over,  his  best  endeavors.  In  nature  the  prevailing  type  is 
a  kind  of  resultant  of  the  highest  fertility  and  the  best  "  fit." 
It  is  not  different  in  our  herds.  The  type  which  naturally  appears 
in  our  herds  will  foe  decided  not  only  by  our  selections  but  by 
the  relative  fertility  and  vigor  of  everything  present. 

Examples  are  not  wanting  in  which  herds,  and  even  whole 
families,  have  gone  down  because  of  this  unequal  battle  against 
the  persistent  influence  of  natural  selection.  The  most  notable 
instance  is  the  "  Duke  and  Duchess  "  family  among  Shorthorns, 
—  most  excellent  individuals  and  true  to  type,  but  not  sufficiently 
prolific  to  maintain  themselves.  So  they  went  down  and  out,  — 
submerged  under  the  inevitable  decree  of  natural  selection  that 
the  unprolific  shall  die.  The  writer  does  not  believe  that  this 
most  excellent  family  need  have  been  lost  to  the  breed  had  the 
breeders  of  the  day  been  sufficiently  alive  to  the  situation.1 

This  response  to  inequality  in  natural  fertility  of  different 
strains  is  technically  known  as  "  genetic  selection,"  and  it  is 
everywhere  at  work.  It  must  be  reckoned  with  in  some  form. 

Physiological  selection.  Certain  individuals  are  sterile  to  each 
other.  It  is  a  difficulty  seldom  encountered,  but  when  it  does 
occur  it  constitutes  an  effective  bar  to  those  particular  blood 
combinations,  however  desirable.  Because  it  is  limited  to  pairs 
of  individuals,  its  interference  is  occasional  rather  than  com- 
mon ;  yet,  when  encountered,  it  should  be  recognized,  and  time 
and  expense  avoided  in  attempts  to  overcome  it. 

Influence  of  age.  Statistics  show  that  a  surprisingly  large 
proportion  of  sires  are  so  young  as  to  be  clearly  immature.  The 
effect  of  this  has  been  much  discussed,  and  the  general  opinion 
seems  to  be  that  breeding  from  immature  animals  is  bad. 

1  This  family  was  always  known  to  be  "  shy  breeders."  The  writer  well 
remembers  hearing  breeders  say,  "  How  fortunate  that  this  is  so,  else  prices  would 
not  be  maintained.'1''  Happy  would  it  have  been  could  these  same  breeders  have 
read  their  doom  in  time  to  save  their  pockets  !  They  had  ample  warning,  had  they 
known  how  to  read  the  handwriting  on  the  wall. 


590  PRACTICAL  PROBLEMS 

In  truth  we  have  little  exact  information  on  which  to  rely,  but 
the  writer  seriously  questions  the  correctness  of  this  conclusion 
from  the  standpoint  of  the  offspring.  That  breeding  at  an  imma- 
ture age  checks  the  growth  of  females  is  next  to  certain,  but  it  is 
also  true  that  the  heifer  will  make  a  better  milker  and  a  more  cer- 
tain breeder  if  bred  before  maturity  and  before  functions  other 
than  milk  production  have  become  the  prevailing  habit  of  life. 

That  the  progeny  of  immature  animals  is  necessarily  faulty 
is  doubtful.  In  nature  everywhere  reproduction  begins  before 
maturity,  and  in  man  at  least  it  has  been  shown  that  the  length 
of  life  of  first  children  is,  on  the  average,  four  years  more  than 
that  of  the  latest  born. 

Considerations  already  advanced  in  connection  with  testing 
breeders  necessitate  the  breeding  at  a  comparatively  advanced 
age,  and  all  things  point  to  the  conclusion  that  in  practice  breed- 
ing may  begin  early  and  continue  as  long  as  possible.  Merely  to 
gain  time,  if  for  no  other  reason,  early  breeding  is  to  be  advocated. 

Blemishes  and  accidental  injuries.  Notwithstanding  popular 
opinion,  the  breeding  animal  is  none  the  worse  for  accidental 
injury ;  that  is,  so  far  as  his  or  her  breeding  value  is  concerned. 
The  question  is  not  whether  the  mare  is  spavined,  but  what  kind 
of  a  hock  had  she  naturally,  and  had  she  sufficient  occasion  to 
be  spavined.  It  is  easy  to  make  a  bad  showing  and  to  say  bitter 
things  about  the  practice  of  breeding  injured  animals,  but  the 
evidence  on  inheritance  all  shows  that  injuries  as  such  are  not 
transmitted.  This  should  not  free  the  mind  from  the  obligation 
to  judge  accurately  as  to  whether  the  part  was  naturally  perfect 
or  naturally  defective. 

Difficulties  in  selection  increase  rapidly  with  the  number  of 
points  on  which  selection  is  to  be  based.  This  purely  mathematical 
consideration  seems  not  to  arrest  the  attention  of  breeders  as  it 
should.  If  we  select  for  one  point  only  we  get  ahead  rapidly. 
That  has  been  the  advantage  of  the  trotter.  Speed  was  the  only 
requirement,  and  while  it  involved  many  subordinate  conditions, 
such  as  a  perfect  body,  vigor,  enduranre,  mental  courage,  and 
determination,  yet  no  other  requirement  has  been  added.  Color, 
size,  style,  action,  conformation,  —  all  have  been  disregarded 
for  the  one  object,  speed. 


SELECTION  591 

Over  against  this  the  Dutch  Belted  Cattle,  for  example,  have 
an  absolute  color  requirement.  Every  cow  must  first  have  a 
white  belt  around  her  body.  This  certainly  has  nothing  to  do 
with  her  milking  abilities,  yet  the  absurd  specification  has  gone 
into  the  very  name  of  the  breed,  —  a  fact  that  will  keep  the 
breed  materially  behind  its  competitors  in  matters  for  which  we 
breed  cows.1 

The  more  clearly  to  show  the  extent  of  the  handicap  of 
striving  after  many  points  in  selection,  let  the  student  work  it 
out  mathematically.  If  but  one  point  is  required,  and  it  can  be 
satisfied,  say  in  one  tenth  of  the  individuals,  then  the  chances 
of  getting  it  are  one  in  ten,  and  one  tenth  of  the  breed  is 
available. 

Now  to  this  let  us  add  a  second  requirement  that  can  be 
found  in  but  one  third  of  the  individuals.  The  probability  of 
finding  these  two  points  in  the  same  individual  will  then  become 
not  y1^  or  J,  but  T^  x  \,  or  ^-,  and  only  about  three  animals 
in  one  hundred  will  meet  the  requirements. 

Need  of  reducing  the  requirements  to  the  utility  basis.  In 
fashionable  animal  breeding  we  have  so  multiplied  our  points 
that  we  are  no  longer  able  to  find  any  very  large  proportion  of 
them  in  any  one  individual,  and  we  are  often  obliged  to  tolerate 
positive  evils  in  order  to  get  the  requirements  even  within  the 
limits  of  the  herd.  This  is  virtually  mixed  breeding. 

What  is  needed  is  a  return  to  first  principles,  —  to  select  a 
very  limited  number  of  the  points  most  important  from  the 
utility  standpoint.  Let  these  be  so  few  and  so  pronounced  that 
they  may  all  be  found  in  every  individual  of  the  breeding  herd. 
Then  later,  as  numbers  multiply,  other  points  can  be  added,  a 
few  at  a  time,  upon  a  practically  pure  ancestry  so  far  as  previous 
points  are  concerned.  "  This  one  thing  I  do  "  should  be  worn  in 
the  hat  of  every  breeder.  A  little  courage  here  would  soon 
work  wonders  ;  but  "  points  "  have  become  so  multiplied  in  some 
of  our  breeds  that  all  possibility  of  finding  any  individuals  that 
possess  them  all  has  long  ago  been  passed,  leaving  us  in  a 

1  The  writer  hesitates  to  use  as  forceful  language  as  the  above  regarding  any 
breed,  because  in  general  all  breeds  are  good,  but  this  is  a  step  so  clearly  adverse 
to  live-stock  interests  that  no  language  is  too  strong  in  condemnation. 


592  PRACTICAL   PROBLEMS 

wellnigh  hopeless  jumble,  with  pedigrees  meaning  next  to  nothing 
so  far  as  definite  information  goes. 

Importance  of  pedigree.  Enough  has  been  shown  to  point 
clearly  to  the  fact  that  the  simply  "  good  individual "  is  worth- 
less as  a  breeder.1  He  must  be  the  product  of  a  good  ancestry, 
and  moreover  of  the  right  kind  of  good  ancestry.  It  is  not 
enough  that  the  animal  or  plant  is  not  mixed  in  its  blood.  We 
ought  to  know,  and  our  pedigrees  ought  to  show,  what  were  the 
special  characters  of  the  ancestors.  There  is  yet  so  much 
variability  in  all  our  breeds  that  a  simple  guaranty  of  non- 
infusion  of  outside  blood  is  not  enough.  Something  positive  is 
needed,  and  great  success  awaits  the  breed  whose  breeders  will 
take  a  few  points  at  a  time  and  establish  a  double  registry,  one  of 
which  shall  be  a  record  of  the  degree  in  which  the  individual 
actually  possessed  the  dominant  characters  of  the  breed.  If  the 
"  advanced  registry  "  of  some  of  the  dairy  breeds  can  be  safe- 
guarded against  abuses,  and  then  be  used  as  a  basis  for  selection, 
it  will  be  of  untold  benefit  to  the  breeds  and  to  the  country  at 
large. 

SECTION  IV  — RATIONAL  SELECTION 

When  and  to  what  extent  to  depart  from  safe  general  prin- 
ciples on  account  of  economic  or  other  considerations  is  a  matter 
calling  for  the  most  discriminating  judgment. 

Fancy  points.  It  is  perfectly  easy  to  show  that  if  the  breeder 
succeeds  in  fixing  really  useful  characters  he  will  have  his  hands 
more  than  full ;  and  yet,  despite  all  this,  fashion  constantly  sets 
certain  fancy  points,  and  insists  upon  their  observance.  The 
trouble  is  not  only  that  most  of  these  fancy  points  have  little  or 
no  utility,  but  also  that,  like  any  other  caprice  of  fashion,  they 
are  likely  to  change  frequently  and  without  warning,  whereas 
all  considerations  of  selection  require  constancy  and  simplicity. 

What,  then,  shall  the  breeder  do  ?  He  is  bent  upon  building 
up  a  herd  of  the  highest  practical  value,  and  he  has  carefully 
weighed  the  relative  value  of  all  utilitarian  characters.  All  of  a 

1  The  regression  table  clearly  shows  that  an  inferior  individual  from  a  good 
ancestry  is  in  every  way  superior  to  a  perfect  individual  from  a  heterogeneous 
ancestry.  Both  are  evils,  but  of  the  two  the  latter  is  by  far  the  worse. 


SELECTION  593 

sudden,  however,  fashion  thrusts  to  the  front  some  absurd 
requirement,  and  insists  that  it  be  met,  or  the  stock  will  remain 
unsold.  The  breeder  is  in  business  not  for  amusement,  but  for 
gain,  as  well  as  for  satisfaction.  He  must  sell  his  product,  or 
very  soon  go  out  of  business.  He  cannot  afford  to  go  on  pro- 
ducing what  nobody  will  buy,  and  he  is  often  brought  face  to 
face  with  the  alternative,  —  financial  ruin,  or  the  destruction  of 
the  herd  from  the  standpoint  of  the  best  breeding. 

For  example,  a  few  years  ago  all  really  good  horsemen  were 
amazed  at  the  demands  of  the  market  for  exceedingly  high 
knee  and  hock  action.  It  was  a  gait  not  only  awkward  to  look 
upon  (except  to  men  who  were  not  horsemen),  but  it  was  exceed- 
ingly hard  on  the  horse,  and  entirely  impractical  except  for 
park  purposes.  Yet  this  was  the  demand,  for  the  time,  on  the 
part  of  the  buyers  who  spent  their  money  freely,  and  it  was 
met  by  the  breeders,  for  such  demands  are  powerful  influences 
in  setting  standards. 

Yet  no  one  knew  better  than  these  same  breeders  that  the 
fashion  was  a  passing  one.  To  what  extent,  then,  should  studs 
be  disturbed,  and  standards  regarding  free,  easy,  and  useful 
action  be  upset  by  a  passing  whim  ?  Requirements  of  fashion 
such  as  these  —  and  they  are  many  and  frequent  in  the  breed- 
ing business  —  call  for  all  the  judgment  of  the  breeder,  and  all 
his  knowledge  and  skill  in  meeting  issues  and  in  freeing  himself 
and  his  herd  or  stud  quickly  from  the  evil  consequences  of  ill- 
advised  standards. 

The  whole  situation  presents  a  case  of  steering  between  diffi- 
culties and  accepting  the  least  of  two  evils,  —  injury  to  the 
breeding  stock  upon  the  one  hand  and  loss  of  sales  upon  the 
other,  and  it  rivals  international  diplomacy  in  the  fineness  of 
distinctions  to  be  observed. 

There  are  two  ways  of  meeting  situations  of  this  kind  with  a 
minimum  of  danger.  One  is  to  meet  the  demand  as  far  as  pos- 
sible by  training  instead  of  breeding  ; l  the  other  is  to  introduce 
whatever  is  to  be  introduced  at  once  in  the  person  of  the  sire, 

1  This  plan  was  actually  used  to  its  limits  in  the  days  of  high  gaits,  when  by 
proper  shoeing,  driving  over  rough  ground,  etc.,  much  was  "  trained  into  "  the 
roadster  being  fitted  for  market. 


594 


PRACTICAL  PROBLEMS 


hoping  the  craze  may  pass  before  the  old  stock  of  females  shall 
pass  away.  If  it  does  not,  then  at  all  hazards  some  remnants 
at  least  must  be  preserved  pure  and  unalloyed  as  a  nucleus 
against  the  day  when  the  pendulum  will  swing  back  to  the 
normal,  or  perhaps  to  the  other  extreme. 

Breeders1  fads.  The  above  has  reference  to  requirements 
imposed  by  the  buyer.  But  the  fact  is,  breeders  themselves 
have  multiplied  their  natural  difficulties  enormously  and  use- 
lessly by  fads  of  their  own  invention,  the  tyranny  of  which  is 
even  worse  than  that  exercised  by  the  alien  buyer.  Against  all 
this  the  strongest  protest  is  far  too  weak. 

Why,  for  example,  should  a  few  curly  hairs  on  the  back  of  a 
hog  disqualify  him  as  a  breeder  ?  Why  are  cows  and  bulls 
selected  by  the  size  or  shape  of  the  escutcheon  ?  Why  must 
a  Jersey  have  a  black  tongue  ?  Why  must  the  tail  bone  of  a 
Holstein-Friesian  cow  reach  to  the  hock  ?  Why  did  the  Shorthorn 
breeders  twenty-five  years  ago  carefully  kill  every  roan  or  white 
calf,  and  so  yield  themselves  to  the  color  craze  that  for  a  decade 
or  more  the  breed  made  progress  backward  ?  Why  such  frantic 
horror  at  the  "  seventeens,"  1  requiring  that  a  book  be  written 
blacklisting  literally  thousands  of  the  best  animals  of  the  breed  ? 

Absurd  standards  of  this  character  should  be  resisted  to  the 
utmost  by  every  reputable  breeder  and  by  every  real  friend  of 
the  breed,  whether  arising  ignorantly  or  from  a  malicious  desire 
to  narrow  the  range  of  possible  sales,  to  discredit  the  animals 
of  competitors,  or  to  destroy  their  herds.  The  writer  is  well 
aware  that  breeders  as  a  class  are  second  to  none,  either  in 
intelligence  or  in  honor.  He  is  aware,  too,  that  many  of  these 
foolish  requirements  or  objections,  like  the  "  querl  "  on  the  pig, 
get  started  no  one  knows  how,  and  gain  strength  by  repetition ; 
but  the  wholesale  destruction  of  reputations,  and  even  of  herds 
and  fortunes,  by  the  war  on  the  " seventeens"  is  convincing  proof 
that  individuals,  even  in  this  honorable  company,  are  not  above 
the  most  dastardly  methods  of  reducing  competition.  Individ- 
uals of  this  sort  are  not  bona  fide  breeders  ;  they  are  commercial 
pirates  who  use  pedigreed  live  stock  as  material  for  speculation. 
They  have  added  nothing  to  the  excellence  of  any  breed,  or  to 

1  Reference  is  here  made  to  the  Shorthorn  importation  of  1817. 


SELECTION 


595 


the  honor  of  breeders,  who,  as  a  class,  are  the  soul  of  honor,  and 
would  no  more  falsify  a  pedigree  than  they  would  rob  a  bank. 

Such  methods  must  be  met,  and  breeders'  fads  generally 
should  receive  their  everlasting  quietus  within  the  confines  of 
our  breeders'  associations.  If  this  may  be,  then  the  individual 
will  be  reasonably  safe  ;  if  not,  then  he  must  take  his  chances 
with  the  rest,  but  against  this  insidious  enemy  of  all  good  breed- 
ing his  voice  and  his  pen  should  be  instant  and  active,  —  this  in 
the  interest  not  only  of  his  own  business  but  of  the  breed  he  loves. 

Fashionable  pedigrees.  All  agree,  and  the  law  of  ancestral 
heredity  proves,  that  the  ancestry  back  of  the  individual  is 
extremely  potent ;  yet  this  potency  largely  resides  in  the  near-by 
members,  and  to  see  a  breeder  poring  over  a  pedigree  running 
ten  or  twelve  generations  back  to  an  "  approved  "  individual  on 
the  female  side,  and  then  gravely  nodding  approbation  of  a 
"  good  foundation,"  —this  is  indeed  both  humorous  and  pathetic. 

According  to  the  law  of  ancestral  heredity  as  stated  by  Galton 
and  fully  noted  in  a  previous  chapter,  each  generation  and  each 
individtial  oi  the  various  generations  has  an  influence  represented 
by  the  following  fractions,  waiving  all  questions  of  prepotency  : 

RELATIVE  INTENSITY  OF  BLOOD  LINES  AND  APPROXIMATELY  RELATIVE 

INFLUENCE  OF  DIFFERENT  GENERATIONS  AND  INDIVIDUALS 

FOR  TEN  GENERATIONS  BACKWARD 


GENERATION 
BACKWARD 

NUMBER  OF 
ANCESTORS 

INFLUENCE  OF  GENERA- 
TION —  PER  CENT 

INFLUENCE  OF  EACH 
INDIVIDUAL  —  PER  CENT 

I 

2 

50.00 

25.00 

2 

4 

25.00 

6.25 

3 

8 

12.5 

1.56  + 

4 

16 

6.25 

0-39+ 

5 

32 

3-^5 

O.IO  — 

6 

64 

1.5625 

0.024  + 

7 

128 

0.78125 

0.006  + 

8 

256 

0.390625 

0.00  1  + 

9 

512 

0.1953125 

0.0004  — 

10 

1024 

0.09765625 

O.OOOI  — 

Total 

2046 

99.90234375  1 

1  This  will  be  100  if  carried  to  infinity. 


596  PRACTICAL  PROBLEMS 

.  By  this  we  see  that  the  individual  inherits  from  no  less  than 
2046  individuals  within  ten  generations  of  ancestry,  and  that, 
on  the  average,  characters  possessed  by  a  single  individual  of 
the  tenth  generation  back  have  an  influence  amounting  to  not 
over  one  ten  thousandth  of  one  per  cent  of  the  total  heritage, 
representing  a  probability  of  about  one  in  a  million  —  certain  to 
be  heard  from  but  of  little  consequence  as  a  foundation. 

We  must  remember  that  besides  the  "foundation"  there  are 
1023  other  ancestors  of  the  tenth  generation,  and  some  1022 
intervening  ancestors,  each  more  powerful  by  far  than  the 
so-called  foundation.  Six  generations  back  the  influence  is  but 
1.5  per  cent  for  the  sixty-four  individuals  involved,  or  about 
-£Q  of  one  per  cent  for  each.  This  is  an  amount  of  influence 
which  for  practical  purposes  may  be  considered  as  a  negligible 
quantity,  and  it  is  for  this  reason  that  in  many  lines  the  dictum 
has  gone  out,  "  The  sixth  cross  is  pure,"  this  meaning  that 
nearly  99  per  cent  is  covered  by  the  "top."  We  have  seen 
already  that  this  agrees  perfectly  with  mathematical  theory. 

The  so-called  foundation  is  therefore  not  a  foundation,  but 
only  a  beginning,  and  it  is  the  /<?/,  and  not  the  bottom,  that  gives 
character  to  the  pedigree. 

This  is  not  intended  to  disparage  purity  of  pedigree  even  to 
the  tenth  generation  and  beyond,  but  it  is  intended  as  a  protest 
against  the  blind  following  of  certain  pedigrees  because  of  the 
"foundation." 

Nor  is  it  to  be  construed  as  a  criticism  directed  against  breed- 
ing along  approved  lines ;  far  from  it ;  but  it  is  a  plea  for  the 
careful  study  and  rational  valuation  of  pedigrees. 

What  deceives  the  breeder  is  the  fact  that  the  "short  form 
pedigree,"  as  it  is  often  presented,  runs  only  on  \kefemale  side,  so 
that,  of  the  2046  ancestors  of  the  first  ten  generations,  only  eight 
or  ten  females  and  their  sires  would  appear  —  the  other  2026 
not  being  noted.  They  exist,  however,  and  their  influence  is  to 
be  reckoned  with.  Of  course  it  is  true  that  in  close  breeding 
the  same  individual  appears  many  times  in  a  pedigree,  and  thus 
his  or  her  influence  is  multiplied ;  but  the  point  here  made  is 
that  a  single  individual  ten  or  even  six  generations  back  counts 
for  little  so  far  as  its  personal  influence  is  concerned. 


SELECTION 


597 


Rational  standards.  In  the  interest  of  rational  breeding,  let 
ideals  be  made  up  of  essentials, — a  few  strong  lines,  which, 
like  the  bold  strokes  of  a  great  painting,  make  the  picture  stand 
strongly  out,  unimpaired  by  a  multitude  of  unimportant  details. 

Summary.  The  whole  purpose  of  selection  is  to  modify  the 
type  to  better  suit  our  purposes,  to  prevent  so  far  as  possible 
the  production  of  undesirable  individuals,  and  to  reduce  the 
population  as  near  as  may  be  to  those  that  are  useful  in  the 
highest  attainable  degree. 

If  the  last  item  is  to  be  accomplished,  then  the  "  pull "  of 
the  ancestry  must  be  in  line  with  the  immediate  parentage,  which 
means  that  there  must  be  a  constant,  not  a  fluctuating,  standard 
of  selection. 

The  probability  of  finding  all  desirable  qualities  in  a  single 
individual  reduces  rapidly  as  the  number  of  characters  multiplies. 
It  is  represented  by  the  product  of  the  chances  of  each,  and  if 
many  characters  are  involved  it  becomes  practically  impossible 
to  find  them  all  in  the  same  individual.  This  leads  inevitably 
to  heterogeneous  breeding  within  the  breed,  and  to  confusion  of 
ancestry  with  respect  to  separate  characters. 

The  practical  way  to  "  fix  "  a  large  number  of  characters  is  to 
do  it  with  one  or  two  at  a  time,  or  at  most  a  few  at  a  time, 
adding  others  as  it  becomes  comparatively  easy  to  secure  them 
all  in  the  same  individual.  Common  sense  dictates  that  we 
should  begin  with  the  most  important  from  the  utility  stand- 
point. In  all  breeds  there  are  too  many  animals  that  do  not 
conform  to  type,  even  approximately,  and  most  standards  of 
selection  call  for  too  many  points. 

Fads  and  fashion,  confined  for  the  most  part  to  minor  matters, 
are  the  bane  of  good  breeding.  They  must  be  reckoned  with  for 
economic  reasons  ;  but  in  the  effort  to  meet  market  demands  it 
is  sometimes  difficult  to  avoid  the  fixing  of  decidedly  objection- 
able characters. 

It  is  the  "top,"  rather  than  the  "  foundation,"  that  gives 
character  to  the  pedigree,  and  in  all  cases  the  individual  should 
conform  to  the  standard  of  selection.  This  calls  for  a  degree  of 
detailed  information  about  individuals  for  at  least  five  or  six 
generations  back,  which  we  do  not  ordinarily  possess,  and  which 


598  PRACTICAL  PROBLEMS 

the  records  do  not  undertake  to  supply,  but  which  breed  histories 
should  afford  for  the  enlightenment  of  young  breeders  and  to 
the  end  that  unfortunate  combinations  may  not  be  unwittingly 
made.  The  student  will  recall  the  difference  between  brothers, 
which  shows  the  need  for  selection  even  within  the  pedigree. 

When  a  family  becomes  famous  it  is  bred  with  less  ability  and 
care  than  before,  whereas  it  is  deserving  of  greater  and  more 
careful  attention.  But  conditions  are  against  it :  the  individuals 
have  a  high  commercial  value,  and  everything  goes  at  a  strong 
price,  indifferent  and  bad  as  well  as  good.  As  long  as  men 
will  pay  for  breeding,  regardless  of  quality,  breeders  are  likely 
to  sell  everything  that  will  find  a  buyer.  A  large  number  of 
breeders  have  reported  to  the  writer  that  they  sell  100  per  cent 
of  their  animals  for  breeding  purposes.  Under  conditions  such 
as  these  all  selection  is  practically  abandoned,  and  we  should  not 
expect  longer  to  maintain  excellence.  Thus  it  is  that  the  very 
success  of  a  popular  strain  is  likely  to  prove  its  undoing. 

This  state  of  affairs  sufficiently  accounts  for  most  disasters  that 
have  overtaken  fashionable  families  in  the  past,  and  we  are  not 
yet  warranted  in  assuming  that  a  favorite  strain  is  bound  quickly 
to  wear  out  or  otherwise  come  to  an  end,  making  it  necessary 
that  we  should  be  forever  effecting  new  combinations.  Indeed, 
there  is  the  best  of  ground  for  the  confident  belief  that  if  a 
tithe  of  the  labor  were  bestowed  upon  the  preservation  of  a  use- 
ful strain  that  was  expended  to  originate  it  we  might  have  it  with 
us  indefinitely,  to  the  infinite  good  of  the  breed  and  the  lasting 
service  of  man.  It  is  not  a  continually  recurring  strain  of  new 
creations  that  is  most  needed,  but  rather  well-protected  and 
solidly  bred  lines  of  long-established  excellence  and  unquestioned 
ancestry.  Here,  in  the  opinion  of  the  writer,  lies  the  field  for 
future  effort  of  American  breeders. 


CHAPTER  XVII 

SYSTEMS  OF  BREEDING 

Of  the  various  possible  systems  of  breeding  some  are  better 
adapted  to  one  purpose,  others  to  another ;  some  again  are 
peculiarly  adapted  to  animals,  and  others  to  plants.  The  practi- 
cal breeder  should  first  of  all  have  a  clear  idea  of  what  he  is 
trying  to  do,  and  then  an  accurate  knowledge  of  the  various 
systems  that  can  be  employed  to  achieve  his  purpose. 

SECTION   I  — PURPOSES  IN   BREEDING 

The  general  principle  that  should  decide  the  system  to  be 
chosen  and  adhered  to  depends  upon  the  answer  to  the  following 
question  :   Is  the  purpose  of  the  breeding  to  improve  the  herd,  — 
that  is,  the  home  stock  of  the  farmer ;  is  it  to  improve  the  breed 
or  variety  as  a  whole ;  or  is  it  to  originate  new  varieties  ? 

The  answer  to  this  question  should  determine  the  system  of 
breeding  to  be  adopted.  These  purposes  are  separate  and  dis- 
tinct. The  first  is  herd  improvement,  the  acknowledged  object 
of  which  is  to  build  up  the  home  stock  until  it  approaches  in 
excellence  the  approved  breeds  or  strains.  This  is  purely  com- 
mercial and  purely  selfish,  in  the  best  sense  of  the  terms,  in  that 
the  breeder  -is  not  operating  for  the  good  of  anybody  or  anything 
but  himself  and  his  own,  and  is  not  aiming  to  outdo  anybody 
else ;  his  purpose  is,  rather,  to  secure  for  himself  the  improve- 
ment that  others  have  originated.  It  is  the  cheapest  and  easiest 
of  all  forms  of  breeding  and  productive  of  the  most  rapid  results. 

The  second  purpose  is,  on  the  other  hand,  chiefly  the  improve- 
ment of  a  recognized  breed  or  variety,  —  an  improvement  in- 
tended to  endow  the  race  more  richly  than  ever  before.  This  is 
the  very  highest  style  of  finished  breeding,  and  calls  for  the  most 
intelligent  and  expensive  methods,  because  in  this  case  the 
breeder  is  a  leader,  not  a  follower  and  an  imitator. 

599 


600  PRACTICAL  PROBLEMS 

The  third  purpose  in  breeding  is  not  to  improve  anything, 
but  to  secure  something  entirely  new,  different  from,  and  pre- 
sumably better  than,  any  previously  existing  strains.  In  carrying 
out  this  purpose  the  breeder  proceeds  upon  the  assumption  that 
our  varieties  are  too  few  ;  that  gaps  exist  which  may  be  filled  up  ; 
and  that  it  is  better  to  produce  something  new  than  to  de- 
pend upon  improving  the  old.  This  is  the  most  ambitious  of  all 
forms  of  breeding,  and  appeals  to  creative  genius  rather  than 
to  conservative  business  instincts,  which  incline  to  improve- 
ment of  existing  races  rather  than  to  the  production  of  new  ones. 
Naturally  it  is  most  common  in  plant  breeding,  in  which  numbers 
are  not  so  serious  a  matter,  and  in  which  breeding  operations  are 
less  expensive. 

As  has  been  remarked,  these  three  purposes  in  breeding  are 
entirely  distinct.  These  distinctions  should  be  clearly  in  the 
mind  of  the  student  when  studying  systems  of  breeding,  and  the 
breeder  himself  must  be  in  no  sense  uncertain  as  to  which  one 
is  really  in  his  mind  when  he  begins  his  breeding  operations. 
If  his  purpose  is  to  improve  his  own,  let  him  frankly  admit  it 
to  himself  and  proceed  accordingly,  leaving  high  prices  and 
hazardous  enterprises  to  others.  If,  on  the  other  hand,  he 
hopes  to  do  something  distinctive  for  his  breed,  and  is  satisfied 
that  he  has  the  money  and  the  patience  to  do  it,  then  again  his 
purpose  is  clear  cut  and  his  methods  are  well  indicated. 

All  breeding  expensive  except  herd  improvement.1  All  forms 
of  breeding  are  costly  whenever  the  purpose  is  to  produce  some- 
thing better  than  ever  before.  If  the  purpose  is  only  to  multi- 
ply excellence,  then  it  is  comparatively  cheap,  but  the  original 
production  of  excellence,  which  is  breeding  in  the  highest 
sense  of  the  term,  is  relatively  expensive,  because  so  few 
individuals,  plant  or  animal,  excel  either  their  predecessors  or 
their  contemporaries,  and  so  few  of  these  can  propagate  their 
own  excellence. 

With  these  considerations  in  mind  it  is  worth  while  to  get  a 
clear  idea  of  the  different  systems  of  breeding  available  for  the 
various  purposes. 

1  "  Herd  improvement "  is  an  expression  used  in  reference  to  the  home  stock, 
•whether  plant  or  animal. 


6oi 


6O2 


PRACTICAL   PROBLEMS 


SECTION  II  — GRADING 

By  "  grading  "  is  meant  the  mating  of  a  common  or  relatively 
unimproved  parent  with  one  that  is  more  highly  improved,  that 
is,  a  "pure  bred."  The  mating  might  be  made  either  way,  but 
in  practice  the  male  is  taken  for  the  pure -bred  parent  for 
economic  reasons.  One  pure-bred  bull  with  a  herd  of  twenty 
cows  can  give  all  the  calves  in  the  herd  a  pure-bred  sire  (that  is, 
make  them  half  bloods),  whereas  if  the  making  of  half  bloods 
were  attempted  in  the  other  way  it  would  require  twenty  pure- 
bred individuals,  and  the  crop  of  calves  would  have  no  more 
improvement ;  besides  which,  the  improvement  made  would  be 
not  in  one  but  in  twenty  lines,  each  with  its  shade  of  difference. 

Expressed  in  terms  of  money,  it  is  possible  to  give  all  the 
calves  in  a  herd. a  pure-bred  sire  —  that  is,  make  them  all  half 
bloods  —  at  a  total  cost  of  approximately  two  dollars  per  calf, 
assuming,  of  course,  a  reasonable  number  of  cows  in  the  herd 
and  a  bull  at  a  moderate  price  but  good  enough  for  grading.  If 
the  making  of  half-blood  calves  were  accomplished  in  the  other 
way,  however,  —  that  is,  by  providing  the  pure -bred  parent  on  the 
dam's  side,  —  it  would  cost,  at  the  same  relative  rate,  close  to 
forty  dollars  as  a  minimum.  This  shows  the  necessarily  extreme 
cost  of  pure  breds  as  compared  with  grades. 

DISAPPEARANCE  OF  UNIMPROVED  BLOOD  BY  THE  CONTINUOUS  USE 
OF  PURE-BRED  SIRES 


SIRES 

DAMS 

OFFSPRING 

GENERATIONS 

Per  Cent  of 

Per  Cent  of 

Per  Cent  of 

Per  Cent  of  Un- 

Purity 

Purity 

Purity 

improved 

I 

TOO 

0 

50     (5) 

50            (-}) 

2 

100 

5° 

75       (!) 

'5            (I) 

3 

IOO 

75 

87-5    (I) 

12.5      U) 

4 

IOO 

87.5 

93-75  (K!) 

6-25     (,',,) 

5 

IOO 

93-75 

96.87  (iji) 

3-"+(A) 

6 

IOO 

96.87 

9844(H) 

i-5+  Mr) 

Improvement  by  grading  is  of  course  limited  to  herd  improve- 
ment.    It  adds  nothing  to  the  breed,  but  it  distributes  breed 


6o3 


604  PRACTICAL  PROBLEMS 

excellence  rapidly  and  with  extreme  certainty.  Such  a  sire  is 
almost  surely  prepotent  over  the  dams,  whatever  they  may  be, 
and  the  mathematics  of  mating  shows  that  if  the  practice  is 
continued  for  six  generations,  but  one  and  a  half  per  cent  of  the 
original  unimproved  blood  will  remain,  as  is  shown  in  the  table 
at  the  bottom  of  page  602. 

By  this  we  see  that  the  unimproved  blood  soon  becomes  insig- 
nificant and  rapidly  disappears.  This  is  why  it  is  that  in  the 
early  days  of  a  breed  the  sixth  or  seventh  cross  is  declared 
eligible  to  record. 

It  should  be  noted  that  if  any  one  of  these  generations  be 
bred  with  itself  (grades  with  grades)  no  progress  is  made.  Thus 
individuals  of  the  second  generation  are  one  fourth  unim- 
proved, and,  bred  to  a  generation  of  their  own  kind,  they  will 
still  remain  one  fourth  unimproved.  By  the  same  principle, 
half  bloods  bred  to  half  bloods  will  produce  half  bloods  indefi- 
nitely. The  effects  of  grading  cease  the  moment  we  discontinue 
the  pure-bred  sire. 

Abuse  of  grading.  The  chief  drawback  in  grading  is  that  it  is 
likely  not  to  be  followed  up.  The  breeder  is  almost  certain  to 
choose  some  promising  half  or  three-quarter  blood  for  a  sire 
because  he  "  looks  as  good"  as  a  pure  bred,  and  then  by  the 
law  of  ancestral  heredity  all  improvement  stops  except  the  little 
that  can  be  accomplished  by  the  slow  process  of  selection. 

Advantages  of  grading.  For  economic  purposes  grades  may  be 
equal  to  pure  breds,  biit  they  are  wortJiless  for  breeding  purposes  ; 
this  is  the  plain  conclusion  of  what  is  well  known  of  the  prin- 
ciples of  breeding.  Grading  is  cheap.  By  the  use  of  a  single 
individual  it  secures  at  once  something  more  than  half  of  the 
total  excellence  of  the  breed,  and  if  followed  up  it  will  secure  in 
time,  through  sires  alone,  practically  all  of  it. 

This  is  the  system  of  breeding  to  be  recommended  to  the 
great  mass  of  stockmen,  and  if  it  could  be  generally  adopted 
and  followed  iip  it  would  add  millions  to  American  agriculture. 
Every  stockman  knows  that  the  great  bulk  of  the  best  cattle  in 
the  markets  are  high-grade  Shorthorns  and  Herefords.  The 
accompanying  figures  surely  show  that  the  less-known  Angus 
and  its  close  relative,  the  Galloway,  arc  equally  successful  for 


SYSTEMS  OF  BREEDING 


605 


grading  purposes.  The  failure  to  make  the  most  of  grading  is 
the  largest  single  mistake  of  American  farmers  and  the  most 
conclusive  evidence  of  shortsighted  business  policy  on  the  part 
both  of  the  general  farmer  and  of  the  breeder  of  pure-bred  stock. 
Breeders  of  pure-bred  stock  largely  to  blame.  When  breeders 
themselves  stop  trying  to  set  up  amateurs,  who  have  little  money 
and  less  experience,  with  small  herds  of  two  or  three  females, 
then  the  longest  step  will  have  been  taken  toward  reform  in  this 


^^^wmH* 


FIG.  48.    Seven-eights  blood  Angus  steers,  six  months  old.  —  Property  of  Hon.  A. 
P.  Grout,  Winchester,  Illinois 

particular.  These  pitifully  inadequate  efforts  at  breeding  are 
foredoomed  to  failure,  after  which  the  unfortunate  farmer,  smart- 
ing under  the  punishment  he  suffered  by  reason  of  his  spasm  of 
enthusiasm  for  better  stock,  forthwith  and  forever  curses  not 
only  the  breed  that  "  let  him  down,"  but  blooded  stock  generally 
and  breeders  in  particular. 

The  breeder's  business  is  the  production  of  sires.  The  profes- 
sional breeder  is  a  producer  of  sires,  and  he  should  sell  males, 
not  females.  He  should  take  the  amateur  kindly  into  his  confi- 
dence and  explain  that  while  he  himself  is  in  the  business  for 
profit,  and  his  animals  are  for  sale,  yet  he  fully  realizes  that 


606  PRACTICAL  PROBLEMS 

grading  is  the  breeding  for  beginners.  He  can  easily  show  the 
novice  that  if  he  will  keep  his  old  females,  or,  if  not,  get  plenty 
of  such  as  are  easily  available,  he  can  have  as  many  grades 
within  a  year  as  he  can  provide  females  now,  and  that  speedily 
he  will  own  a  herd  that  for  all  practical  purposes  except  breed- 
ing will  be  as  good  as  anybody's,  all  at  a  cost  of  only  two  or 
three  dollars  per  calf,  and  correspondingly  less  or  more  for  other 
animals.  Such  a  course  will  demonstrate  at  once  the  excellence 
of  the  breed,  and  make  friends,  not  enemies,  of  the  man  and 
his  neighbors. 

The  burden  is  upon  the  breeders  and  owners  of  pure-bred 
flocks  and  herds  to  lead  in  a  crusade  for  grading.  They  need 
the  market  for  their  excess  of  males,  and  if  this  market  were 
fully  developed,  and  the  mass  of  stockmen  fully  alive  to  the 
advantages  of  grading,  this  market  alone  would  absorb  at  good 
prices  all  the  male  output  from  our  breeding  herds,  —  a  consum- 
mation they  stand  sorely  in  need  of  attaining. 

The  female  output  of  our  breeding  herds  should  be  used,  first, 
to  reenforce  the  home  herds,  and  after  that  to  supply  deficiencies 
in  other  reputable  herds.  Any  further  surplus  animals  should  go 
to  the  open  market,  except  in  some  rare  cases  in  which  they  are 
needed  for  the  real  founding  of  new  herds. 

The  main  difficulty  is  that  the  breeders,  as  a  rule,  are  too 
intent  upon  selling  females  and  setting  up  a  multitude  of  little 
breeders  in  a  small  business ;  whereas  they  should  be  not  only 
intent,  but  persistent,  in  selling  males  for  grading  purposes. 
This  is  their  great  market,  their  natural  outlet,  and  its  exploita- 
tion is  their  opportunity.  The  author  has  replies  from  hundreds 
of  breeders  on  this  point.  A  large  share  of  them  profess  to  ex- 
pend as  much  effort  to  sell  females  as  to  sell  males,  and  a  few 
even  more.  Associations  have  much  to  do  along  this  line. 

Begin  animal  breeding  by  grading.  Grading  is  the  safest  begin- 
ning, even  for  the  prospective  breeder  of  pure-bred  stock.  Not 
only  is  it  cheap  and  safe,  but  it  will  bring  out  clear  and  strong  in 
the  grades  the  main  breed  points,  and  a  few  generations  of  grades 
from  low  to  high  will  spread  out  before  the  eyes  of  the  breeder 
such  a  panorama  of  breed  characters  as  he  would  not  see  in 
years  of  pure  breeding  on  a  small  scale  ;  indeed,  there  is  no 


6o7 


608  PRACTICAL  PROBLEMS 

quicker,  cheaper,  or  more  thorough  way  of  becoming  acquainted 
with  a  breed  than  through  its  grades. 

Disadvantage  of  grading.  The  only  disadvantage  that  can  be 
mentioned  is  this,  —  that  the  first  results  are  so  eminently  satis- 
factory that  some  promising  grade  is  likely  to  be  selected  as  a 
sire,  regardless  of  the  law  of  ancestral  heredity,  whereupon  all 
further  improvement  stops.  This  is  so  likely  to  be  the  case  that 
it  may  be  said  in  general  that  the  very  success  of  grading  is  the 
greatest  guaranty  of  its  failure. 

SECTION   III  —  CROSSING  OR  HYBRIDIZING 

Almost  the  exact  opposite  of  grading,  crossing  combines 
ancestral  lines  of  two  distinct  races,  breeds,  or  varieties,  in  the 
hope  either  of  securing  a  blend  or  else  of  getting  a  fortuitous 
combination  of  characters. 

This  form  of  breeding  is  adapted  only  to  the  production  of 
new  strains,  in  which  it  excels.  Of  course  it  so  mixes  blood  lines 
as  to  effectually  destroy  the  influence  of  the  ancestry  and  all 
meaning  and  value  of  pedigree.  Its  hope  is  in  starting  a  new 
strain,  which  may  perchance  breed  pure. 

The  operation  of  Mendel's  law  teaches  how  small  is  this 
chance.  If  this  law  always  held  with  all  races  and  characters, 
it  would  of  course  be  impossible  to  secure  permanent  strains 
by  crossing,  but  the  fact  remains  that  permanent  hybrids  have 
frequently  been  secured  by  this  method,  especially  among  plants, 
which  is  a  noteworthy  fact  in  breeding. 

Advantages  of  crossing.  Notwithstanding  the  operation  of 
Mendel's  law  as  a  general  principle,  crossing  is  a  fruitful  source 
of  new  strains.  Hybridization  is  better  adapted  to  plants  than 
to  animals  because  of  the  need  of  vigorous  selection  afterward 
and,  therefore,  of  relatively  large  numbers.  It  was  a  favorite 
method  of  plant  improvement  twenty  years  ago,  but  it  has  fallen 
largely  into  disuse  because  of  the  inconstancy  of  Mendel's 
middle  term  (the  50  per  cent  apparent  hybrids)  and  because  as 
good  or  better  results  can  often  be  secured  by  selection  alone, 
without  destruction  of  the  pedigree  and  the  influence  of  the 
ancestry. 


SYSTEMS  OF  BREEDING  609 

Disadvantages  of  crossing  (hybridizing).  The  difficulty  of 
securing  a  blend  out  of  a  violent  cross,  or  indeed  anything 
that  will  breed  pure,  and  the  great  mass  of  long-continued  and 
disappointing  reversions  experienced,  have  turned  the  attention 
largely  away  from  this  system  of  breeding,  to  one  which,  if  less 
spectacular,  is  eminently  safer,  and,  so  far  as  we  now  know, 
fully  as  fruitful  of  results. 

It  is  the  opinion  of  the  writer,  however,  that  as  we  learn  by 
experience  it  will  be  found  that  certain  races  of  plants  will  lend 
themselves  well  to  this  means  of  producing  new  varieties,  and 
that  the  old-time  enthusiasm  for  hybridization  will  return  in 
these  exceptional  cases. 

Crossing  is  a  powerful  means  of  inducing  variability, — indeed, 
it  is  the  most  powerful  method  known  to  breeders.  It  is  alto- 
gether too  fruitful  of  variants  to  be  manageable  in  animal  breed- 
ing, and  only  sheer  necessity,  after  all  other  methods  have  failed, 
would  warrant  its  trial  among  these  slow-breeding  races. 

If  animals  are  to  be  hybridized  it  can  probably  best  be 
accomplished  by  combining,  not  two  races  simply,  but  three  or 
more,  leaving  the  one  nearest  that  which  is  wanted  untouched 
until  a  fairly  favorable  cross  between  two  others  has  been  secured. 
Then  the  pure  form,  if  bred  with  the  cross,  might  be  influenced 
thereby,  but  would  of  course  remain  prepotent.  Such  a  plan  of 
action  aims  rather  at  the  modification  of  a  breed  than  at  the 
creation  of  a  new  one. 

Hybrids  often  sterile.  All  degrees  of  productivity  are  found 
in  hybrids,  from  extreme  fertility  to  absolute  sterility.  Some 
crosses  are  more  fertile  than  either  parent.  Such  a  cross  would 
be  made  readily  in  nature.  Others  are  absolutely  or  nearly  sterile. 
It  is  safe  to  assume  that  about  all  the  possible  fertile  hybrids 
were  long  ago  produced  in  nature,  and  either  went  down  under 
natural  selection,  or  became  good  species  before  they  came  into 
our  hands.  However,  modified  strains  may  yet  be  hybridized, 
and  sterile  hybrids  may  often  be  propagated  asexually. 

The  classic  hybrid  is  the  mule  or  hinny,  the  cross  between  the 
horse  and  the  ass,  and  is  nearly  always  sterile.  The  lion  and  the 
tiger  mate  freely,  in  captivity  at  least,  but  the  mating  is  in  most 
cases  fruitless.  Even  here,  however,  hybrids  have  been  born. 


PRACTICAL  PROBLEMS 

The  reciprocal  cross.  Strange  as  it  may  at  first  appear,  the 
two  possible  crosses  by  interchange  of  the  sexes  often,  though 
not  always,  differ  substantially.  It  is  said  that  the  common 
mule  more  nearly  resembles  the  ass,  and  the  hinny  the  horse. 
Other  instances  have  been  noted,  and  the  point  has  been  urged 
that  reciprocal  crosses  are  in  general  dissimilar.  It  is  the 
writer's  opinion  that  the  rule  applies  only  to  those  particular 
characters  in  which  the  one  parent  (either  male  or  female)  is 
prepotent  over  the  other  because  of  sex.  However,  statistical 
evidence  on  reciprocal  crosses  is  almost  totally  lacking. 

The  whole  subject  of  hybridization  seems  at  present  to 
promise  little  of  interest  to  animal  breeders  beyond  the  produc- 
tion of  the  common  mule,  but  if  we  may  place  a  shrewd  guess, 
it  will  yet  be  found  a  fruitful  source  of  new  varieties  in  certain 
races  of  plants,  in  which  propagation  is  so  easily  effected  by 
budding,  grafting,  or  other  form  of  asexual  multiplication,  thus 
avoiding  the  effects  of  Mendel's  law  in  a  way  quite  impossible 
with  animals. 


SECTION  IV  — LINE  BREEDING 


By  "  line  breeding  "  is  meant  the  restriction  of  selection  and 
mating  to  the  individuals  of  a  single  line  of  descent.    The  pur- 
pose of  this  system  of  breeding  is  real  breed  improvement,  — 
to  get  the  best  that  can  be  gotten  out  of  the  race,  and  better 
than  ever  before  if  possible. 

Experience  has  shown  that  if  the  purpose  be  breed  improve- 
ment, or  even  herd  improvement  carried  to  its  limits,  it  is  not 
enough  to  confine  selection  to  the  limits  of  the  breed.  All 
breeds  are  exceedingly  variable,  and  real  results  aiming  at  any- 
thing more  than  mere  multiplication  can  follow  only  closely 
drawn  lines  within  the  breed, — breeding  in  line,  or  line  breeding. 

Line  breeding  excludes  everything  outside  the  approved  and 
chosen  line  of  breeding.  It  not  only  combines  animals  very 
similar  in  their  characters,  but  it  narrows  the  pedigree  to  few 
and  closely  related  lines  of  descent.  This  ''purifies"  the  pedi- 
gree rapidly  and  gives  the  ancestry  the  largest  possible  oppor- 
tunity. The  system  is  eminently  conservative.  It  discourages 


SYSTEMS  OF   BREEDING 


6l 


variability,  and  rapidly  reduces  it  to  a  minimum.  Moreover, 
whatever  variations  do  occur  will  be  in  line  with  the  prominent 
diameters  of  the  chosen 
branch  of  tJie  breed. 

Advantages  of  line 
breeding.  The  nature  of 
results  secured  by  this 
system  can  almost  cer- 
tainly be  predicted  ;  and 
when  they  do  appear,  and 
improvement  is  at  hand, 
it  is  backed  up  by  the 
most  powerful  hereditary 

influence    obtainable,    be-     FIG.  50.  Baron  Duke  63d,  a  line-bred  Berkshire. 


Property  of  A.  J.  Lovejoy,  Rosco,  Illinois. 
Figures  51  and  52  show  get  of  this  boar 


cause  of  the  simplicity 
and  strength  of  the  an- 
cestry, which,  if  the  selection  has  been  good,  all  "  pulls  "  in  the 
same  direction.  The  records  of  all  breeds  will  show  the  pro- 
nounced results  that  have  followed  judicious  line  breeding.  A 
volume  could  be  filled  with  pictures  of  famous  animals  so  pro- 


FIG.  51.    Line-bred  Berkshire  pigs.    Get  of  Baron  Duke  63d 

duced.    Those  shown  are  of  swine,  for  the  reason  that  the  pig  is 
popularly  supposed  to  be  the  most  sensitive  to  close  breeding. 

Disadvantages  of    line  breeding.    The   chief    danger  in  line 
breeding  is  that  the  breeder  will  select  by  pedigree,  abandoning 


612  PRACTICAL  PROBLEMS 

real  individual  selection.  A  line-bred  pedigree  is  valuable  or 
dangerous  in  exact  proportion  as  the  individuals  have  been  kept 
up  to  grade.  It  will  not  replace  selection,  but,  on  the  contrary, 
calls  for  the  most  discriminating  care  within  the  line. 

If  the  breeder  selects  by  paper,  and  not  in  the  yards,  and  a 
few  generations  of  inferior  animals  creep  in,  then  line  breeding 
will  consign  the  whole  bunch  to  the  limbos  quicker  and  more 
certainly  than  will  any  other  known  system  of  breeding,  —  a 


FIG.  52.    Line-bred  yearling  Berkshires.    Get  of  Baron  Duke  6jd 

fate  that  has  overtaken  more  than  one  line  that  unfortunately 
became  prematurely  fashionable. 

Line  breeding  the  best  system  for  improvement.  No  other 
system  of  breeding  has  ever  secured  the  results  that  line  breed- 
ing has  secured,  and  if  the  present  state  of  knowledge  is  reason- 
ably sound,  no  other  system  will  ever  be  so  powerful  in  getting 
the  most  possible  out  of  a  given  breed  or  variety,  especially  of 
animals,  and  this  with  the  greatest  certainty  as  we  go  along. 
The  only  requirement  is,  not  to  abandon  individual  selection.  A 
pedigree  is  not  a  crutch  on  which  incompetence  can  lean ;  it  is 
a  guaranty  of  blood  lines,  —  a  field  inside  of  which  breeding 
operations  and  selection  may  with  confidence  be  confined. 

The  word  "  confined  "  is  used  advisedly,  for,  after  line  breed- 
ing has  been  practiced  for  a  few  generations,  the  ancestry 
becomes  a  kind  of  pure  breed  of  its  own,  —  a  breed  within  a 
breed,  so  to  speak,  —  and  any  attempt  to  introduce  blood  from 


SYSTEMS  OF   BREEDING  613 

other  lines  is  likely  to  be  followed  by  the  pains  and  penalties  of 
hybridization ;  for  a  departure  from  line  breeding  is  a  kind  of 
crossing  in  a  small  degree,  and  so  rapidly  do  blood  lines  become 
intensified  that  line-bred  animals  assume  all  the  attributes  of 
distinct  strains,  as  they  in  truth  are,  and  they  will  be  likely  to 
behave  as  such  ever  after. 

In  saying  that  line-bred  animals  tend  to  behave  like  pure 
strains,  and  that  their  progeny  from  union  with  other  strains 
behave  like  hybrids,  it  is  not  meant  that  such  unions  should 
never  be  made,  or  that  such  behavior  is  as  persistent  as  with 
real  crosses.  In  truth,  many  lines  are  so  stubborn  as  never  to 
blend  with  others  afterward  (behaving  like  the  most  strongly 
established  races),  but,  on  the  other  hand,  most  of  them  will 
yield  to  well-directed  and  persistent  effort ;  that  is  to  say,  a 
line-bred  herd  can  be  modified,  and  in  time  made  to  assume  the 
characters  of  another  family,  but  the  process  is  attended  with  a 
struggle  and  not  a  few  failures.  It  has  been  fashionable  at 
times  to  decry  line  breeding,  but  the  fact  remains  that  a  few 
generations  of  good  breeding  soon  bring  the  herd  and  its  career 
to  a  point  where  line  breeding  must  be  practiced  or  a  worse 
alternative  must  be  accepted,  for  with  well-selected  strains  all 
outbreeding  is  mixed  breeding. 

SECTION  V  — INBREEDING 

Line  breeding  carried  to  its  limits  involves  the  breeding 
together  of  individuals  closely  related.  When  it  involves  the 
breeding  together  of  sire  and  offspring  or  of  dam  and  offspring 
or  of  brother  and  sister,  it  becomes  inbreeding,  or  "  breeding  in 
and  in."  It  is  line  breeding  carried  to  its  limits,  and  of  course 
possesses. all  the  advantages  and  disadvantages  of  that  form  of 
breeding  carried  to  their  utmost  attainable  degree. 

Forms  of  inbreeding.  Three  forms  of  inbreeding  are  possible 
among  animals,  namely  : 

i.  Breeding  the  sire  upon  his  daughter,  giving  rise  to  off- 
spring three  fourths  of  whose  blood  lines  are  those  of  the  sire, 
—  a  practice  which,  if  followed  up,  soon  results  in  offspring  with 
but  one  line  of  ancestry,  thus  practically  eliminating  the  blood 


6 14  PRACTICAL  PROBLEMS 

of  the  dam.    This  form  of  breeding  is  practiced  when  it  is  de- 
sired to  secure  all  that  is  possible  of  the  blood  of  the  sire. 

2.  Breeding  the  dam  to  her  own  son  or  sons  successively, 
thus  increasing  the  blood  lines  of  the  female  side.    This  form  is 
practiced   when    it    is   the   dam's    blood   lines   that  are   to    be 
preserved  and  condensed.    Both  systems  are  necessarily  limited 
to  the  lifetime  of  the  individuals  involved.     Either  system  can 
of  course   be   approximated   by  the   use   of   granddaughter   or 
grandson,  which  would  by  common  consent  be  called  inbreed- 
ing, but  relationship  more  remote  would  generally  be  regarded 
merely  as  line  breeding. 

3.  Breeding  together  of  brother  and  sister,  —  a  form  of  in- 
breeding which  preserves  the  blood  lines  from  both  sire  and  dam 
in   equal  proportions.    It  is  inferior  to  either  of  the  others  as  a 
means  of  strengthening  previously  existing  blood  lines,  but  it  is 
freely  employed  when  the  combination  has  proved  exceptionally 
successful,  virtually  establishing  a  new  type.    It  has  all  the  dangers 
of  the  other  two,  and  in  a  larger  degree,  because  we  have  prac- 
tically  no  acquaintance  with  the  new  combination,  whereas  in 
strengthening  the  proportion  of  one  line  of  ancestry  over  another, 
whether  it  be  that  of  the  sire  or  that  of  the  dam,  we  are  dealing 
with  previously  existing  blood  lines  known  to  be  harmonious. 

Among  plants  there  are  two  forms  of  inbreeding,  namely  : 

1.  That  in  which  the  fertilization  is  with  pollen  from  another 
flower  on  the  same  plant. 

2.  That  in  which  fertilization  is  by  pollen  of  the  same  flower. 
This,  being  hermaphroditic,  is  the  closest  imaginable  inbreeding, 
and  exceeds  anything  that  is  possible  with  animals. 

Advantages  of  inbreeding.  Nobody  claims  advantages  in  in- 
breeding  per  se,  but  it  is  the  acme  of  line  breeding,  and  when 
superior  individuals  are  at  hand  it  is  the  most  powerful  method 
known  of  making  the  most  of  their  excellence.  It  is  the  method 
by  which  the  highest  possible  percentage  of  the  blood  of  an 
exceptional  individual  or  of  a  particularly  fortunate  "  nick  "  ran 
be  preserved,  fused  into  and  ultimately  made  to  characterize  an 
entire  line  of  descent  on  both  sides. 

If  persisted  in,  the  outside  blood  disappears  by  the  same  law 
that  governs  grading,  and  the  pedigree  is  speedily  enriched  to 


SYSTEMS  OF   BREEDING  615 

an  almost  unlimited  extent  by  the  blood  of  a  single  animal,  - 
in  practice,  generally  that  of  the  sire.    It  is  a  method  not  so 
much  of  originating  excellence  as  of  making  the  most  of  it  when 
it  does  appear,  and  it  is  not  too  much  to  say  that  a  large  pro- 
portion of  the  really  great  sires  have  been  strongly  inbred. 

An  inbred  animal  is  of  course  enormously  prepotent  over 
everything  else.  Its  half  of  the  ancestry,  being  largely  of  iden- 
tical blood,  is  almost  certain  to  dominate  the  offspring.  Inbreed- 
ing is,  therefore,  recognized  as  the  strongest  of  all  breeding, 
giving  rise  to  the  simplest  of  pedigrees,  —  an  advantage  quickly 
recognized  when  we  recall  the  law  of  ancestral  heredity.  In  this 
respect  it  is  all  that  line  breeding  is  and  more. 

A  second  advantage  is  that  successful  associations  of  char- 
acters are  preserved  intact  and  not  shattered  by  the  infusion  of 
new  strains.  If  the  breeder  were  dealing  with  but  a  single  char- 
acter he  could  readily  find  its  equal,  and  there  would  be  little 
need  for  inbreeding ;  but  even  if  breeding  for  but  a  single  utili- 
tarian character,  he  always  has  at  least  two  others,  vigor  and 
fertility,  which  must  be  included  in  selection.  In  practice  he  has 
many  more,  and  a  single  individual  that  contains  all  or  most  of 
them  in  a  high  degree  is  a  veritable  bonanza ;  naturally  the 
temptation  is  to  make  the  most  of  an  opportunity  which  is  none 
too  frequent  in  the  breeding  business. 

All  things  considered,  no  other  known  method  of  breeding 
equals  this  for  intensifying  blood  lines,  doubling  up  existing 
combinations,  and  making  the  most  of  exceptional  individuals 
or  of  unusually  valuable  strains. 

Disadvantages  of  inbreeding.  Clearly,  however,  this  is  not  a 
gun  to  uhit  the  bear  and  miss  the  calf."  This  "doubling  up" 
process,  this  intensifying  of  characters,  increasing  their  prospects 
from  possibility  to  probability  and  afterward  to  certainty,  works 
exactly  the  same  for  one  character  as  for  another ;  it  affects  all 
characters  of  tJic  individuals  involved,  bad  as  well  as  good;  and 
so  it  is  that  this  method,  which  is  applicable  to  both  plant  and 
animal  breeding,  and  which  aims  at  making  the  greatest  use 
possible  of  our  most  valuable  possessions,  has  been  followed 
alike  by  the  most  strikingly  successful  results  and  by  the  most  - 
stupendous  disasters  that  ever  overtook  the  breeding  business. 


616  PRACTICAL  PROBLEMS 

Plenty  of  examples  of  successes  can  be  instanced,  and  every 
breeder  is  familiar  with  them.  The  failures  have  been  many, 
but  they  are  not  to  be  counted  here,  for  the  blood  lines  in- 
volved are  long  since  extinct. 

Special  dangers  from  inbreeding.  Tradition  everywhere  has  it 
that  inbreeding,  if  long  continued,  is  practically  certain  to  end 
in  loss  of  vigor  and  of  fertility,  and  plenty  of  instances  are  given 
to  "prove"  it. 

Now  a  rational  consideration  of  the  principles  of  transmission 
has  already  led  us  to  expect  that  bad  characters  as  well  as  good 
will  be  intensified.  We  could  not  expect  so  powerful  a  method 
to  work  only  to  our  advantage  and  to  grant  immunity  from  dis- 
advantage in  all  cases. 

What  we  want  to  know  is  whether,  in  respect  to  trouble, 
we  are  to  look  out  for  likelihood  or  for  certainty ;  whether  disas- 
ter is  inevitable,  or  only  extremely  probable.  This  question  has 
been  much  befogged  by  certain  catchy  statements  such  as, 
"  Nature  abhors  incestuous  breeding,"  all  of  which  confuse  an 
ethical  and  social  question  with  the  biological  one  in  which  only 
we  are  interested. 

Inbreeding  not  necessarily  disastrous.  Our  attention  is  con- 
stantly called  to  "  nature's  provisions  for  preventing  inbreeding," 
and  to  "  ingenious  devices  for  inducing  cross  pollination  by 
insect  aid  "  ;  but  we  are  not  reminded  that  many  species  of 
plants  are  self -pollinated,  nor  is  our  attention  called  to  the  many 
famous  sires  that  were  strongly  inbred,  nor  to  the  fact  that  in 
nature  among  gregarious  animals  the  head  of  the  herd  is  sire  of 
practically  all  the  young  (so  long  as  he  remains  master),  many  of 
of  whom  are  thus  doubly  his.  Nor  do  we  have  it  called  to  our 
attention  that,  while  corn  seems  peculiarly  sensitive  to  inbreed- 
ing, wheat  is  self-fertilizing  to  the  closest  possible  degree,  and 
that  it  is  perhaps  the  most  vigorous,  prolific,  and  all-round  cos- 
mopolitan success  among  our  domestic  plants. 

Lack  of  vigor  and  low  fertility  the  two  most  common  defects. 
If  what  has  been  said  and  shown  has  any  meaning,  it  is  that  any 
character  can  be  bred  up  or  down,  strengthened  or  weakened 
by  this  method  of  breeding.  Why  then  its  evil  reputation  with 
respect  to  vigor  and  fertility  ?  Is  there  some  inherent  injury 


SYSTEMS  OF  BREEDING  617 

from  close  breeding,  or  is  it  merely  that  vigor  and  fertility  are 
commonly  defective  characters  and  frequently  find  themselves 
on  the  losing  side  ?  Undoubtedly  it  is  the  latter.  There  are 
cases  enough  of  the  greatest  vigor  and  fertility  of  inbred  indi- 
viduals, and  of  family  lines  and  even  of  whole  species,  to  set 
aside  all  fear  of  inevitable  injury  from  close  breeding,  but  a 
little  study  will  convince  us  that  there  is  lurking  weakness  and 
infertility  everywhere.  It  is  said  that  one  third  of  our  children 
die  in  infancy.  A  large  proportion  of  animals  and  an  apparently 
larger  proportion  of  plants  are  relatively  weak  and  easily  suc- 
cumb to  disease  or  to  the  encroachments  of  their  neighbors. 

Few  individuals  are  fully  fertile,  —  that  is,  free  and  regular 
breeders,  — and  fewer  yet  are  both  fertile  and  vigorous.  Short- 
comings in  these  two  respects  may  be  called  the  distinguishing 
defects  of  both  plants  and  animals  under  domestication.  In 
nature  they  constitute  the  chief  points  of  attack  of  natural  selec- 
tion, but  in  domesticated  animals  and  plants  we  commonly  select 
for  other  points,  even  color,  trusting  to  luck  for  vigor  and  fertility. 
Is  it  any  wonder  that  these  lurking  evils  have  crept  upon  us 
until  they  often  constitute  an  insurmountable  bar  to  inbreeding, 
and  have  invaded  even  our  most  carefully  outbred  herds  ? 

As  inbreeding  is  the  supreme  test  of  a  race,  so  it  is  of  a  char- 
acter ;  if  a  character  suffers  by  inbreeding  it  is  a  sign  of  natural 
defectiveness  and  should  be  accepted  as  such,  and  not  laid  up 
as  an  additional  instance  and  a  weapon  with  which  to  abuse  a 
system  with  a  history  of  laudable  achievement  in  the  past  and 
rich  with  possibilities  for  the  future. 

When  we  select  for  vigor  and  fertility  we  shall  hear  less  of  the 
evils  of  inbreeding.  In  the  meantime  we  shall  hear  most  about 
it  where  vitality  and  fertility  are  naturally  lowest.  Both  are 
cardinal  requisites,  —  one  for  life,  the  other  for  reproduction,  — 
and  both  must  be  possessed  in  a  high  degree  by  any  individual 
or  family  line  that  is  to  figure  much  in  descent. 

Noting,  then,  the  remarkable  instances  of  successful  inbreed- 
ing, as  well  as  its  unexampled  capacity  for  trouble,  we  arrive 
at  the  conclusion  that  the  disaster  from  inbreeding  is  probable, 
but  not  inevitable.  With  that  much  gained,  it  is  worth  while  to 
examine  further  into  this  disputed  territory. 


6i8  PRACTICAL   PROBLEMS 

Darwin's  experiments.1  Fortunately  so  far  as  plants  are  con- 
cerned we  are  not  without  some  accurate  data  tending  to  show 
the  actual  effect  of  inbreeding  upon  the  two  most  important 
characters  here  under  discussion,  —  namely,  vigor  and  fertility, 
—  and  for  a  great  variety  of  species.  The  experiments  are  too 
extensive  to  fully  discuss  even  by  abstract,  covering  as  they  do 
some  fifty-seven  species,  belonging  to  fifty-two  genera ; 2  but 
their  results  may  be  briefly  stated. 

The  careful  study  of  these  experiments  shows  the  following 
facts  :  (i)  that  in  general,  and  without  a  doubt,  crossed  forms 
(both  they  and  their  offspring)  are,  on  the  average,  much  more 
fertile  and  far  more  vigorous  than  are  the  self-fertilized  ;  (2)  but 
that  this  is  not  true  of  all  species,  nor  is  it  true  of  all  individuals, 
even  within  those  species  most  sensitive  to  inbreeding. 

Thus,  of  the  83  species  tested  for  height,  26,  or  nearly  one 
third,  were  either  within  5  per  cent  of  the  height  of  their  cross- 
bred companions,  or  else  exceeded  them  in  height.  Of  these  26 
cases,  however,  he  concludes  that  14  were  actually  inferior,  — if 
not  in  height,  at  least  in  other  respects,  —  leaving  12,  or  one 
seventh  of  all,  that  quite  clearly  were  not  inferior  when  inbred, 
and  in  some  cases  were  decidedly  the  better  for  it.3  Concluding, 
Darwin  remarks  : 

Therefore  if  we  exclude  the  species  which  are  approximately  equal,  there 
are  thirty-seven  species  in  which  the  mean  of  the  mean  heights  of  the 

1  Charles   Darwin,  Cross  and  Self  Fertilization  in  the  Vegetable  Kingdom, 
p.  482  [D.  Appleton  &  Company].    It  is  unfortunate  that  we  do  not  possess 
equally  full  and  exact  data  as  to  inbreeding  among  animals,  but  at  this  point  our 
knowledge  is  limited  to  general  results  and  to  individual  experiences.    The  marked 
success  of  close  breeding  and  even  inbreeding  in  our  herds  is  attributed  to  the 
special  skill  of  a  "  master  breeder."    That  this  is  not  the  full  explanation  is  shown 
by  the  experience  of  the  United  States  Bureau  of  Animal  Industry.    Some  years 
ago  it  became  necessary  to  remove  the  stock  of  guinea  pigs  to  new  quarters  a 
considerable  distance  away.    A  severe  storm  was  encountered  en  route  and  only  a 
few  pigs  were  saved.    From  these  few,  and  with  no  infusion  of  outside  blood,  the 
present  stock  is  descended,  and  the  writer  is  credibly  informed  that  the  stock  is 
exceptionally  vigorous  and  fertile. 

2  The  student  desiring  the  data  upon  the  effects  of  cross-  or  self-fertilization  in 
general  should  read  chap,  vii,  pp.  238-284,  of  Darwin's  Cross  and  Self  Fertiliza- 
tion, etc. ;  for  data  concerning  the  effect  upon  seed  production  he  should  read 
chap,  ix,  pp.  312-355  ;  and  for  data  concerning  other  effects,  chap,  viii,  pp.  285-31 1 ; 
for  detailed  reports  of  different  species  see  chaps,  ii-vi,  especially  ii. 

3  Darwin,  Cross  and  Self  Fertilization,  etc.,  pp.  279-283, 


SYSTEMS  OF  BREEDING  619 

crossed  plants  exceeds  that  of  the  self-fertilized  by  22  per  cent,  whereas 
there  are  only  five  species  in  which  the  mean  of  the  mean  heights  of  the 
self -fertilized  plants  exceeds  that  of  the  crossed,  and  this  only  by  9  per  cent.1 

The  writer  again  calls  attention  to  the  fact  that  while  averages 
are  of  prime  consequence  in  commercial  transactions,  they  do 
not  decide  principles  of  breeding,  and  it  is  extremely  suggestive 
that  even  five  species  were  decidedly  more  vigorous  when  inbred. 
It  determines  definitely  that  there  is  nothing  inherently  and 
necessarily  evil  in  inbreeding,  per  se,  for  if  such  were  the  case  it 
would  make  itself  evident  in  every  instance. 

Speaking  of  the  fertility  of  self -fertilized  flowers,  Darwin  says,2 
"  Their  fertility  ranges  from  zero  to  fertility  equaling  that  of  the 
crossed  flowers  ;  and  of  this  fact  no  explanation  can  be  offered." 
Not  only  was  this  true,  but  the  self -fertilized  forms  were  some- 
times actually  more  fertile  than  the  crossed.3 

This  mystery,  for  which  "  no  explanation  can  be  offered,"  is 
largely  cleared  up  by  our  modern  knowledge  of  heredity,  as 
is  shown  by  what  follows. 

The  total  effects  of  inbreeding.  All  characters,  both  good  and 
bad,  exist  in  various  degrees  in  different  individuals.  The  prob- 
lem in  breeding  is  to  secure  the  strongest  combinations  of  desir- 
able characters,  and  it  is  easy  to  show  that  this  is  accomplished 
by  inbreeding.  Not  only  that,  but  it  is  also  easy  to  show  that 
the  same  methods  will  secure  the  lowest  attainable  intensity,  — 
a  consummation  desirable  with  unwelcome  characters,  and  good 
to  know  about  as  a  general  possibility. 

Take,  for  example,  three  intensities  of  any  single  character, 
disregarding  for  the  moment  all  questions  of  correlation.  Let 
these  three  intensities  be  represented  by  3,  2,  and  I,  respec- 
tively, 2  being  the  mean. 

If,  now,  we  exclude  inbreeding,  we  find  three  unions  possible, 
-namely,  3  +  2,  3+1,  and  2  +  i  ;  but  if  we  resort  to  inbreed- 
ing, we  make  also  the  matings  3  +  3,2  +  2,  i  +  I.    Which  unions 
are  richest  in  results  ?    In  which  have  blood  lines  been  most 
intensified  ? 

1  Darwin,  Cross  and  Self  Fertilization,  etc.,  p.  283. 

2  Ibid.  p.  326. 

3  Ibid.  pp.  322-325. 


620  PRACTICAL  PROBLEMS 

RELATIVE  EFFECT  OF  OUTBREEDING  AND  OF  INBREEDING 


MATING 

MID-PARENTS 

OFFSPRING 

• 

3  +  2 

Outbreeding                 .    •< 

3  +  2 

3  +  i 

-  2.5 

3  +   * 

2 
2  +   I 

• 

2   +   1 

2 

-  !-5 

i 

3  +  3 

3  +  3 

2 

2+2 

=  3 

2  +  2 

,:. 

L 

I   +   I 

2 

From  this  we  see  that  both  systems  produce  the  same  mean, 
but  that  inbreeding  produces  the  wider  extremes  (3  and  i). 
Hence  the  greatest  range  of  possibilities  lies  with  inbreeding,  so 
far  as  immediate  parentage  alone  is  concerned,  and  the  advantage 
is  of  course  still  greater  in  the  ancestry  farther  back. 

Again,  the  table  shows  what  will  happen  on  the  average  under 
the  law  of  regression,  but  in  exceptional  cases  the  law  of  pro- 
gression will  apply,  from  which  we  see  that  the  advantage  for 
inbreeding  is  still  greater ;  in  other  words,  it  is  by  inbreeding 
that  the  highest  and  the  lowest  attainable  results  can  be  pro- 
duced, and  this  is  because  no  other  system  can  produce  so  high 
(or  low)  a  mid-parent,  or  in  the  end  so  "  pure  "  an  ancestry.  All 
of  this  indicates  a  principle  that  is  abundantly  powerful  for 
intensifying  good  characters  or  for  breeding  out  evil  ones.  The 
fact  that  it  is  thus  powerful  argues  against  its  use  with  any  but 
superior  individuals.  Furthermore,  inbreeding  is  a  supreme  test 
of  excellence,  and  if  a  family  line  or  an  individual  endures  it,  its 
characters  are  above  reproach. 

Not  all  inbred  individuals  inferior  to  the  cross-bred,  even  in 
species  especially  sensitive  to  inbreeding.  One  of  Darwin's  most 
extensive  series  of  experiments  was  carried  on  with  the  common 


SYSTEMS  OF   BREEDING 


621 


morning-glory  (Ipomcea  purpured)!  This  species  was  bred  both 
crossed  and  self -fertilized  for  ten  generations.  In  every  genera- 
tion the  crossed  forms  were  larger  than  the  self -fertilized,  the 
average  being  as  100  is  to  77.  Not  only  that,  but  they  were 
clearly  the  more  productive.  The  species,  therefore,  is  one  that 
on  the  whole  is  extremely  sensitive  to  inbreeding.  Let  us,  how- 
ever, analyze  the  details  of  the  experiment  and  observe  how  it 
fares  with  individual  plants. 

Darwin's  plan  was  to  put  the  cross  and  the  inbred  seeds  into 
moist  sand  at  the  same  time,  and  then  to  pair  them  off  in  the 
order  of  their  germination.  That  is,  the  first  cross-bred  seed  up 
would  be  paired  with  the  first  inbred  seed  up  as  a  competitor,2 
the  two  being  planted  on  opposite  sides  of  the  same  pot ;  the 
second  would  be  paired  with  the  second,  the  third  with  the  third, 
and  so  on.3 

The  following  table,  reporting  the  first  generation,  shows  how 
the  results  appeared  at  first.  H£IGHTS  QF  CROSS.BRED  AND  IN_ 

The  average  of  these  six  BRED  STOCK)_FIRST  GENERATION* 
pairs  is  86  inches  for  the 
cross-bred  and  65.6  for  the 
self -fertilized,  an  initial  differ- 
ence of  approximately  20 
inches,  which  on  the  whole 
did  not  greatly  change  during 
the  ten  generations  of  the  ex- 
periment. 

It  will  be  noted  that  in  this 
table  every  inbred  plant  is 
inferior  to  its  cross-bred  mate ; 
not  only  that,  but  no  inbred 
individual  of  the  series  is  as  good  as  the  poorest  cross-bred 
reported. 

1  Reported  in  full  in    Darwin's  Cross  and  Self  Fertilization,  etc.,  chap,  ii, 
pp.  28-62. 

2  If,  however,  a  seed  germinated  long  before  a  corresponding  mate  appeared, 
it  was  thrown  away,  the  aim  being  to  mate  seedlings  that  germinated  exactly 
together,  giving  an  even  start. 

3  Darwin,  Cross  and  Self  Fertilization,  etc.,  pp.  n,  12. 

4  Ibid.  p.  29. 


NUMBER  OF 
POT 

CROSSED 

INBRED 

I 
In  pairs 

87.5  in. 
87.5 
89 

69  in. 
66 

73 

2 

In  pairs 

88  in. 

87 

68.5  in. 
60.5 

3 
Plants  crowded 

77  in. 

57  in- 

622 


PRACTICAL  PROBLEMS 


NUMBER  OF 
POT 

CROSSED 

INBRED 

I 

84  in. 

47 

80  in. 
44-5 

2 

83  in. 
59 

73-5  in- 
5i-5 

82  in. 

56.5  in. 

3 

65.5 
68 

63 

52 

On  this  point  compare  the  facts  reported  in  the  following 
table  for  the  fourth  generation.1 

Here  again  each  inbred  plant  is  inferior  to  its  particular  mate, 
but  only  three  of  the  cross-breds  equaled  the  best  inbred  plant 

of  the  series  (80  inches),  and 
all  but  one  of  the  inbreds  were 
more  vigorous  than  the  poor- 
est cross-bred. 

The  same  general  fact  is 
noticeable  in  the  next  (fifth) 
generation,  though  not  quite 
so  pronounced,  except  that  in 
one  case  the  inbred  plant 
equaled  its  own  mate.  Evi- 
dently something  was  prepar- 
ing to  happen. 

The  appearance  of  "  Hero."  In  the  next  (sixth)  generation 
there  appeared  a  specially  vigorous  plant  that  overtopped  its  own 
competitor  by  half  an  inch  and  exceeded  in  height  all  but  three 
of  the  series.  Darwin  named  this  plant  "  Hero,"  and  remarks, 
"  I  was  so  much  surprised  at  this  fact  that  I  resolved  to  ascertain 
whether  this  plant  would  transmit  its  powers  of  growth  to  its 
seedlings." 

Accordingly  he  fertilized  a  number  of  flowers  of  Hero  with 
their  own  pollen,  and  planted  the  seedlings  in  competition  with 
other  inbred  plants  and  with  cross-bred  as  well.  The  two  tables 
on  the  next  page  show  how  the  descendants  of  Hero  acquitted 
themselves. 

Here,  then,  out  of  a  species  sensitive  to  inbreeding,  has  arisen 
a  plant  that  is  strong,  vigorous,  and  prolific,  and  its  own  inbred 
seedlings  at  once  demonstrate  their  superiority  not  only  to  other 
inbred  stock  but  also  to  their  crossed  competitors.  As  Darwin 
remarks,2  "  Hero  transmitted  to  its  offspring  a  peculiar  consti- 
tution adapted  for  self-fertilization";  and  again,3  "It  appears, 
therefore,  that  Hero  and  its  descendants  have  varied  from  the 
common  type  not  only  in  acquiring  great  power  of  growth  and 

1  Darwin,  Cross  and  Self  Fertilization,  etc.,  p.  34. 

2  Ibid.  p.  50.  3  Ibid.  51. 


SYSTEMS  OF  BREEDING 


623 


increased  fertility  when  sub-    OFFSPRING  OF  HERO  COMPARED  WITH 
jected  to  self-fertilization,  but       ORDINARY  INBRED  SEEDLINGS,  — 

SEVENTH  GENERATION  OF 
INBREEDING 


NUMBER  OF 

CHILDREN 

ORDINARY 

POT 

OF  HERO 

INBRED 

74  in. 

89.5  in. 

I 

60 

61 

55-25 

49 

92  in. 

82  in. 

2 

91-75 

56 

74-25 

38 

OFFSPRING  OF  HERO  COMPARED  WITH 

CROSS-FERTILIZATION  SEEDLINGS, 

—  SEVENTH  GENERATION  OF 

INBREEDING 


in  not  profiting  from  a  cross 
with  a  distinct  stock." 

Here  is  excellence  through 
inbreeding  under  what  may 
be  called  the  hardest  condi- 
tions, and  it  gives  great  en- 
couragement to  the  belief  that 
if  it  is  necessary  to  secure  a 
strain  of  plant  or  animal  that 
will  prosper  under  inbreeding, 
that  strain  can  be  produced, 
and  that  its  production  is  a 
question  only  of  time,  pa- 
tience, and  expense.  Hero  will 
undoubtedly  be  called  a  mu- 
tant in  these  days,  but  mutants 
are  welcome.  It  must  be  borne 
in  mind  that  Hero  was  not  the 
only  individual  that  demon- 
strated its  superiority  to  cross- 
bred plants,  but  that  this  was 
a  common  circumstance 
throughout  the  experiments. 

Nor  was  the  morning-glory 
the  only  case  of  the  kind.  Con- 
cerning his  experiments  with  Mimulus  (the  monkey-flower,  of  no 
consequence  to  us  except  as  showing  a  principle)  he  says : l 

In  the  third  and  fourth  generations  a  tall  variety,  often  alluded  to,  hav- 
ing large  white  flowers  blotched  with  crimson,  appeared  amongst  both  the 
intercrossed  and  the  self-fertilized  plants.  It  prevailed  in  all  the  later  self- 
fertilized  generations,  to  the  exclusion  of  every  other  variety,  and  trans- 
mitted its  characters  faithfully,  but  disappeared  from  the  intercrossed 
plants.  .  .  .  The  self-fertilized  plants  belonging  to  this  variety  were  not  only 
taller  but  more  fertile  than  the  intercrossed  plants,  though  these  latter  in 
the  earlier  generations  were  much  taller  and  more  fertile  than  the  self- 
fertilized  plants. 

1  Darwin,  Cross  and  Self  Fertilization,  etc.,  p.  348.    (Italics  are  mine.) 


NUMBER  OF 
POT 

CHILDREN 
OF  HERO 

CROSS-BRED 

' 

92  in. 

76.75  in. 

2 

87 
87-75 

89  in. 
86.75 

624  PRACTICAL  PROBLEMS 

He  adds,1  "  This  variety  seems  to  have  become  specially  adapted 
to  profit  in  every  ^vay  by  self-fertilization^  although  this  process 
was  so  injurious  to  the  parent  plants  during  the  first  four  genera- 
tions." Darwin's  whole  discussion  of  "highly  self-fertile  varie- 
ties "  2  is  exceedingly  valuable,  not  only  because  the  author  seems 
to  consider  the  phenomena  inexplicable,  but  more  especially  be- 
cause it  establishes  the  fact  that  the  closest  inbreeding  is  not 
necessarily  fatal. 

It  should  be  noted,  however,  that  these  are  exceptional  in- 
stances, constituting  no  argument  for  indiscriminate  inbreeding, 
but  they  do  show  that  inbreeding  is  not  necessarily  headed 
straight  for  disaster  and  with  a  full  head  of  steam. 

The  breeding  business  deals  not  with  averages  but  with  pos- 
sibilities, and  it  is  high  time  that  the  foolish  horror  of  inbreed- 
ing be  dissipated.  If  breeders  had  been  as  careful  in  certain 
other  respects  as  they  have  been  to  avoid  the  slightest  form  of 
inbreeding,  our  flocks  and  herds  would  have  progressed  farther 
along  the  road  of  improvement. 

Experience  in  animal  breeding.  Any  one  who  will  take  the 
trouble  to  study  the  pedigrees  of  famous  families  in  almost  any 
line  of  stock  breeding  will  find  that  the  foundation  blood  is 
most  intensely  bred.  Indeed,  the  practical  breeder  working  with 
material  that  is  really  of  distinctive  and  peculiar  merit  comes 
soon  to  the  point  at  which  close  breeding  is  inevitable,  and  he 
must  face  the  issue  sooner  or  later  if  he  is  to  make  any  real  use 
of  his  valuable  creations.  To  breed  them  out  is  but  to  dissipate 
their  excellence,  and  the  only  practical  course  is  close  breeding. 

Among  cattle  breeders  this  practice  is  too  well  known  to 
need  more  than  a  passing  mention,  but  the  following  extracts 
from  personal  letters  recently  received  will  show  how  it  works 
upon  the  highly  organized  horse  and  the  quick-breeding,  heavy- 
fleshed  swine. 

The  veteran  breeder  of  Arab  horses,  Randolph  Huntington, 
of  Rochester,  New  York,  writes  as  follows  : 

With  me  close  breeding  has  proved  a  sure  test  for  purity,  and  my  best, 
most  uniform  results  have  been  in  breeding  the  dam  to  her  son  and  to  her 

1  Darwin,  Cross  and  Self  Fertilization,  etc.,  p.  348.    (Italics  are  mine.) 

2  Ibid.  pp.  347-3S2- 


SYSTEMS  OF   BREEDING  625 

grandson,  and  then  breeding  the  produce  together,  intensifying  such  breeding 
by  going  back  to  the  grand-dam  with  the  grandchildren,  until  I  had  a  family. 

In  this  connection  we  do  not  forget  that  Messenger  was 
three  times  inbred  to  Godolphin. 

The  following  from  A.  J.  Lovejoy,  of  Roscoe,  Illinois,  gives 
his  experience  in  breeding  Berkshires.  The  quality  of  his  stock 
is  indicated  by  Figs.  50-52,  and  his  reputation  as  a  successful 
breeder  is  fairly  won  by  many  years  of  uniform  success.  He 
writes  as  follows  : 

We  are  believers  in  quite  close,  even  inbreeding.  We  find  the  greatest 
show  animals  are  closely  inbred.  Sires  to  half-sisters  is  the  most  common 
form  of  close  breeding,  though  cousins,  nephews,  and  nieces,  and  even 
brothers  and  sisters  are  bred  together  with  great  success.  It  of  course 
requires  good  judgment  in  mating  animals  that  are  particularly  strong  in 
individual  merit.  Should  each  have  a  bad  defect  in  any  way,  we  should 
expect  that  to  be  more  manifest  in  the  offspring  than  in  the  parents,  and 
likewise  the  good  points  would  be  better ;  so  if  one  mates  equally  good 
specimens  the  produce  will  be  an  improvement.  There  is  no  sire  of  any 
breed  so  prepotent  as  an  inbred  sire.  When  we  get  to  the  point  where  we 
feel  the  need  of  outside  blood  we  mate  an  imported  sow  with  our  best  boar, 
and  from  this  litter  we  select  a  boar  to  use  on  the  get  of  his  own  sire  from 
other  sows  in  the  herd  ;  that  is,  we  breed  this  boar  on  his  own  half-sisters. 

No  man  has  bred  Berkshires  more  successfully  than  N.  H. 
Gentry,  of  Sedalia,  Missouri,  and  no  American  breeder  has  been 
credited  with  a  freer  use  of  inbreeding.  This  veteran  breeder 
writes  as  follows  : 

My  experience  in  inbreeding  is  that  you  do  good,  or  fail,  in  proportion 
to  the  quality  in  the  strain  of  blood ;  that  is,  that  you  intensify  what  you 
have,  let  it  be  good  or  bad,  let  it  be  weak  or  strong  in  constitution.  The 
theory  advanced  by  the  mass  of  people,  to  the  effect  that  you  degenerate 
size  and  weaken  constitution,  is  all  wrong  unless  the  strain  you  are  inbreed- 
ing lacks  size  as  a  rule,  or  lacks  constitution.  Animals  that  have  plenty  of 
size  and  a  vigorous  constitution  can  have  these  traits  intensified  as  certainly 
as  you  can  lessen  these  traits  by  inbreeding  with  strains  lacking  these 
essential  traits.  If  you  can  intensify  the  one  it  seems  to  me  as  reasonable 
that  you  can  the  other ;  so  a  man's  success  in  inbreeding  will  depend  upon 
what  he  has  to  inbreed  with.  Rightly  and  intelligently  done  I  have  never 
been  able  to  detect  any  bad  results  whatever  from  inbreeding.  I  inclose 
you  my  prize  list  of  two  World's  Fairs,  and  it  is  especially  true  of  my 
St.  Louis  winners  that  every  animal  was  closely  inbred.  It  has  always 
been  strange  to  me  that  most  every  person  who  has  never  given  the  subject 


626  PRACTICAL   PROBLEMS 

any  study  whatever  has  a  decided  notion  that  inbreeding  is  dangerous.  I 
presume  our  fathers  tell  us  this  simply  because  their  fathers  told  them  so 
and  their  grandfathers  before  them,  and  not  one  in  many  thousands  has 
ever  given  the  matter  any  trial  or  serious  thought.  Even  with  a  trial  it 
does  not  follow  that  every  case  will  be  a  success,  any  more  than  the  mating 
of  animals  not  related  will  be  a  success  in  every  case.  The  animals  mated, 
whether  kin  or  not,  must  be  suited  to  produce  good  results  ;  that  is,  have 
no  weakness  in  common,  and  as  much  good  as  possible. 

How  to  practice  inbreeding.  There  are  two  situations  espe- 
cially indicating  this  method  of  breeding.  One  is  grading,  in 
which  it  may  ordinarily  be  practiced  with  impunity.  The  other 
arises  in  the  very  best  herds  when  the  breeder  finds  himself  in 
possession  of  a  small  amount  of  very  superior  blood  and  is  debat- 
ing how  to  handle  it.  If  he  insists  upon  breeding  "out"  he 
will  lose  it  by  dissipation.  He  has  gone  to  the  limits  of  line 
breeding  ;  what  shall  he  do  ? 

In  a  case  of  this  kind  the  only  course  that  promises  anything 
is  inbreeding.  It  puts  the  line  to  the  severest  possible  test,  of 
course,  and  the  hazard  is  great,  but  the  possible  results  are 
phenomenal.  The  really  good  breeder  should  always  be  ready 
to  accept  whatever  hazard  is  involved. 

If  it  is  to  be  done  at  all,  the  best  way  is  to  "do  it  and  be 
done  with  it,"  and  know  the  worst  at  once.  Many  breeders, 
fearing  the  consequences,  go  at  the  job  gingerly,  breeding 
a  little  more  closely  with  each  successive  trial,  as  if  to  test  the 
situation  before  making  the  bold  and  final  stroke.  This,  if  not 
successful,  is  to  undermine  the  situation  and  accumulate  num- 
bers of  undesirable  individuals  ;  in  any  event  it  consumes  time 
that  is  valuable,  for  animals  grow  old  quickly. 

The  proper  way  is  to  make  the  boldest  stroke  at  once,  so  that, 
if  the  worst  happens,  the  original  stock  is  left  for  other  trials 
and  the  breeder  is  not  possessed  of  a  herd  that  is  destroyed  by 
unsuccessful,  half-hearted  attempts  at  inbreeding. 

SECTION  VI  — BREEDING  FROM  THE  BEST 

This  has  reference  to  the  practice  of  selecting  and  breeding 
from  the  best  individuals  but  without  reference  to  blood  lines. 
It  is  probable,  indeed  it  is  certain,  that  in  process  of  time 


SYSTEMS  OF   BREEDING  627 

exceedingly  valuable  races  could  be  established  in  this  way, 
especially  on  restricted  areas  and  more  particularly  with  field 
crops. 

But  in  actual  practice  the  breeder  following  this  method 
among  animals  succeeds  in  getting  together  a  confused  jumble, 
out  of  which  nothing  of  note  can  be  established.  It  is  the 
practice  followed  by  primitive  races  and  by  careless  farmers, 
and  as  soon  as  some  attention  is  paid  to  strains,  to  families, 
and  to  blood  lines,  it  passes  at  once  into  some  one  of  the  other 
forms  of  breeding  already  discussed. 

In  plant  breeding  the  principle  operates  differently.  Here 
numbers  may  be  employed  so  extensively  that  after  having 
chosen  the  stock  we  can  literally  hunt  through  thousands  for 
the  thing  we  want.  This  when  found  is,  strictly  speaking,  a 
mutant,  and  having  found  it  the  plant  breeder  may  proceed  at 
once  to  multiply  it  by  cuttings  or  to  breed  it  pure,  possibly  by 
inbreeding,  certainly  with  as  little  crossing  as  possible.  This  is 
the  system  followed  by  Luther  Burbank,  and  by  plant  breeders 
generally  who  are  looking  for  new  things,  though  it  is  often 
combined  with  crossing. 

Neither  in  animal  nor  in  plant  breeding,  however,  are  we  to 
expect  much  success  except  by  regarding  ancestral  lines  and 
living  and  working  in  full  realization  that  the  law  of  ancestral 
heredity  is  a  fact. 

Summary.  The  system  of  breeding  to  be  followed  depends 
upon  the  purpose  to  be  accomplished.  Grading  is  the  practical 
method  of  improving  common  stock  and  of  quickly  and  cheaply 
getting  acquainted  with  the  essential  characters  of  a  breed. 

If  the  purpose  is  breed  improvement  through  the  perfection 
of  family  lines,  then  line  breeding  and  even  inbreeding  will  be 
the  systems  found  most  effective. 

If  new  types,  new  strains,  and  new  creations  generally  are 
sought,  two  courses  are  open, —  either  to  watch  for  accidental 
mutations,  or  to  hasten  their  appearance  by  crossing,  a  form 
of  breeding  that  produces  individuals  which  are  good,  but  which, 
under  the  common  law  of  ancestral  heredity,  are  too  bad  mix- 
tures to  produce  a  uniform  type,  and  under  Mendel's  law  are  too 
unstable  to  produce  a  constant  type  of  any  kind.  The  system 


628  PRACTICAL  PROBLEMS 

of  crossing  is,  therefore,  best  adapted  to  plants,  which  can  be 
propagated  asexually,  and  therefore  free  from  the  limitations 
just  mentioned. 

SPECIAL  EXERCISES 

Make  calculations  showing  the  relative  expense  of  grading  as  compared 
with  breeding  pure  for  different  classes  of  animals. 

Also  make  critical  study  of  many  pedigrees  of  famous  animals  in  order 
to  trace  the  systems  of  breeding  actually  employed,  especially  as  to  line 
breeding  and  inbreeding. 


ADDITIONAL  REFERENCES 

Loss  OF  VIGOR  FROM  INBREEDING.    By  H.  J.  Webber.    Science,  1901, 

No.  320,  p.  257. 
POLLINATION    OF    APPLES    AND    PEAS.     Experiment    Station    Record, 

XIII,  620. 
RECIPROCAL    CROSSES    (with    extended   bibliography).     Maine    Station 

Report,  1904,  pp.  81-89. 


CHAPTER  XVIII 

THE  DETERMINATION  OF  SEX 
SECTION  I  — THEORIES 

The  desire  to  control  the  sex,  or  at  least  to  predict  what  it 
will  be,  is  a  very  old  and  a  very  common  one.  There  are 
apparently  about  as  many  theories  purporting  to  cover  the  case 
as  human  ingenuity  has  been  able  to  devise  (more  than  five 
hundred  are  now  known),1  and  as  there  is  but  one  alternative  in 
the  case,  any  theory,  no  matter  how  absurd,  is  certain,  under  the 
law  of  probabilities,  to  come  true  half  the  time.  Some  of  the 
principal  theories  that  have  gained  popular  credence,  and  which, 
so  far  as  present  knowledge  goes,  contain  no  basis  of  truth,  are 
the  following : 

1.  That  one  testicle  is  naturally  male,  the  other  female,  and 
that  the  sex  will  depend  upon  the  source  of  the  particular  sper- 
matozoon taking  part  in  fertilization.  —  Disproved  by  the  fact 
that  males  with  but  one  testicle  are  yet  able  to  sire  both  sexes. 

2.  That  successive  ova  are  alternately  male  and  female,  so 
that  naturally  the  sexes  would  be  evenly  distributed,  and  all 
that  is  needed  to  produce  sex  at  will  is  to  choose  the  proper 
heat  for  service  ;  that  is  to  say,  if  the  last  young  were  a  female, 
then  service  at  the  first,  third,  fifth,  etc.,  heats  thereafter  would 
produce  males,  and  at  the  second,  fourth,  sixth,  etc.,  heats  would 
result  in  females.  —  Disproved  in  the  same  way  as  is  the  first 
theory ;   that   is  to  say,  females  with  but  one  ovary  produce 
both  sexes,  and  the  same  sex  is  repeated  indefinitely,  with  no 
alternation  in  heats. 

3.  That  the  stronger  personality,  especially  in  a  sexual  sense, 
will  impress  its  sex  upon  the  offspring.  —  Disproved  by  the  fact 
that  parents  of  both  sorts  produce  both  sexes  freely,  and  by  the 
further  fact  that  in  general  sires  are  better  bred  and  stronger 

1  Geddes  and  Thomson,  Evolution  of  Sex,  p.  35. 
629 


630  PRACTICAL  PROBLEMS 

specimens  than  are  dams,  which  should  give  a  heavy  prepon- 
derance of  males,  —  a  fact  not  substantiated. 

4.  That  service  early  in  heat  will  produce  a  male  (some  say  a 
female),  and  that  service  late  in  heat  (with  ovum  stale)  will 
produce   the  opposite   sex.  —  Disproved   by   the    fact    that    in 
nature  females,  especially  in  herds,  are  served  early  in  heat,  — 
a  fact  that  should  make  the  offspring  practically  all  of  one  sex. 

5.  That  the  older  parent  will  determine  the  sex,  —  some  say 
the  parent  nearest  the  prime  of  life ;  not  substantiated. 

6.  That  extreme  sexual  excitement  on  the  part  of  the  female 
is  almost  certain  to  result  in  male  (some  say  female)  offspring. 
This  is  a  difficult  assumption  to  prove  or  to  disprove,  because 
everything  turns  upon  what  would  be  called  extreme  excitement, 
and  the  singular  fact  is  that  the  believers  in  this  theory  them- 
selves appear  quite  unable  to  decide  which  sex  is  indicated  by 
the  violent  disturbances  of  the  female ;  some  say  one,  some  say 
the  other,  until  it  looks  like  a  case  of  the  indigo  test  over  again. 

It  is  inconceivable  that  the  general  disturbance  of  the  body 
attending  heat  should  have  the  slightest  influence  upon  the 
character  of  the  union  of  the  nuclear  matter  of  two  germ  cells, 
which  is  all  that  we  now  know  to  be  involved  in  fertilization. 

It  is  noticeable  that  nearly  every  theory  on  determination  of 
sex  contains  some  trace  of  "  male  superiority,"  many  going  so 
far  as  to  state  that  females  are  undeveloped  males.  This  con- 
ceit is  evidenced  wherever  an  advantage  is  supposed  to  exist,  as 
by  excess  of  fertilization,  —  such  advantage  being  always  given 
to  the  male. 

Any  theory  not  involving  obscure  distinctions  —  as  does  this 
one  —  can  be  easily  proved  or  disproved  by  the  statistical 
method,  always  remembering  that  a  correlation  up  to  50  per 
cent  is  inevitable,  indicating  no  cause  at  work  but  chance.  It 
is  far  more  profitable  to  leave  speculation  and  inquire  what  is 
actually  known  about  the  causes  that  determine  sex. 

Sex  differences  slight.  First  of  all,  the  idea  of  fundamental 
sex  differences  is  greatly  exaggerated.  About  the  only  attribute 
that  can  be  ascribed  to  "  maleness  "  in  general  throughout  the 
whole  range  of  life  is  a  little  higher  state  of  activity,  usually  but 
not  always  accompanied  by  somewhat  decreased  size.  Typically 


THE   DETERMINATION  OF  SEX  631 

the  ovum  is  large,  well  supplied  with  nourishment,  and  not 
given  to  activity ;  while  the  sperm  plasm,  spermatozoon,  or 
pollen  grain,  is  small,  and  poor  in  food  material,  but  character- 
ized by  great  activity. 

Aside  from  this,  males  and  females  differ  far  less  than  is 
popularly  supposed.  The  artificial  conventionalities  and  the  es- 
tablished divisions  of  labor  exaggerate  differences  of  sex  in  man, 
and  over-enthusiastic  writers  have  formed  out  of  these  exaggera- 
tions conclusions  as  far-reaching  as  they  are  grotesque. 

Sex  differences  are  few  and  slight,  and  mostly  connected  with 
the  serious  business  of  reproduction.  We  need  not,  therefore, 
in  seeking  causes  for  their  determination,  look  for  such  as  strike 
at  the  very  foundation  of  racial  characters.  Sex  is  something 
superimposed  upon  all  other  considerations  —  not  a  fundamental 
division  halving  the  population  into  one  section  that  may,  and 
another  that  may  not,  enter  into  the  full  possession  of  all  the 
endowments  of  the  race. 

SECTION  II  —  INFLUENCE  OF  NUTRITION 

In  tadpoles.  According  to  Pfliiger,1  three  forms  develop : 
(a)  distinct  males,  (b]  distinct  females,  and  (c)  hermaphrodites. 
In  the  last  case  the  male  organs  "  develop  round  primitive 
ovaries,  and  if  the  tadpoles  are  to  become  males  the  inclosed 
female  organs  are  absorbed." 

According  to  Young,2  sex  in  tadpoles  remains  a  long  time 
indeterminate,  and  during  this  time  the  amount  of  food  exerts 
a  controlling  influence  upon  the  sex.  He  had  three  broods  of 
tadpoles. 

Brood  i,  under  natural  conditions,  developed  54  per  cent 
females,  but  when  fed  freely  with  beef  it  developed  females  in 
the  proportion  of  78  per  cent;  the  proportion  of  females  from 
brood  2  was  increased  by  a  generous  diet  of  fish,  from  61  per 
cent  to  8 1  per  cent ;  and  in  the  same  way  a  diet  of  frogs'  flesh 
raised  the  proportion  in  brood  3  from  56  per  cent  when  "left 
alone  "  to  92  per  cent  when  fed,  —  all  of  which  looks  as  though 
nutrition  has  some  influence  upon  sex  in  frogs  at  least. 

1  Geddes  and  Thomson,  The  Evolution  of  Sex,  p.  45.  2  Ibid. 


632  PRACTICAL   PROBLEMS 

In  plant  lice.1  In  general  it  may  be  said  that  in  summer, 
when  favorable  conditions  of  life  are  at  the  maximum,  these 
creatures  produce  parthenogenetically  generation  after  genera- 
tion, and  only  females,  but  with  the  cool  of  autumn  and  its 
lessened  food  supply,  males  appear,  and  sexual  reproduction  is 
resumed ;  indeed,  to  quote  from  Geddes  and  Thomson,2  "  in 
the  artificial  environment  of  a  greenhouse,  equivalent  to  a  per- 
petual summer  of  warmth  and  abundant  food,  the  partheno- 
genetic  succession  of  females  has  been  experimentally  observed 
for  four  years.  It  seems  in  fact  to  continue  until  lowering  of 
the  temperature  and  diminution  of  food  reintroduce  males  and 
sexual  reproduction."  Others  have  stated  that  males  may  be 
produced  at  any  time  merely  by  letting  the  plants  on  which  the 
lice  are  feeding  become  somewhat  "dried  up." 

SECTION  III  —  INFLUENCE  OF  FERTILIZATION 

In  bees.3  As  is  now  well  known,  bees  are  of  three  forms  as 
regards  sex,  —  drones  (males),  produced  from  unfertilized  eggs  ; 
workers  (females,  generally  but  not  always  sterile),  produced 
from  fertilized  eggs ;  and  queens  (fertile  females),  also  pro- 
duced from  fertilized  eggs  but  quartered  in  special  cells  and 
given  large  amounts  of  special  food.  As  remarked  by  Geddes 
and  Thomson,  "  royal  diet  and  plenty  of  it  develops  the  repro- 
ductive organs  of  the  future  queens,"  and  at  any  time  "  within 
the  first  eight  days  of  larval  life  the  addition  of  a  little  food  will 
determine  the  striking  structural  and  functional  difference 
between  worker  and  queen."  4  This  fact  is  often  taken  advan- 
tage of  by  the  nurse  bees  when  disaster  threatens  through  the 
loss  of  the  queen  cells.  Hastily  extracting  some  worker  larvae 
from  their  ordinary  cells,  they  deposit  them  in  the  queen  cells, 
giving  them  royal  food,  and  speedily  they  acquire  all  the  charac- 
ters of  any  other  fertile  queen,  —  a  result  plainly  due  either  to 
the  character  or  to  the  quantity  of  the  food,  or  to  both. 

In  the  case  of  bees,  therefore,  fertilization  seems  to  be  the 
deciding  factor  as  to  differences  between  male  and  female,  and 

1  Geddes  and  Thomson,  The  Evolution  of  Sex,  p.  49. 

2  Ibid.  p.  50.  3  Ibid.  pp.  46-48.  *  Ibid.  p.  47. 


THE   DETERMINATION   OF  SEX 


633 


food  the  element  that  determines  whether  or  not  the  female  is 
to  be  fertile.  This  is  a  sex  distinction  that  cannot  hold  in  the 
higher  forms,  where  fertilization  is  necessary  to  development, 
whatever  the  sex,  showing  that  one  species  may  differ  from 
another,  even  in  seeming  fundamentals,  and  teaching  us  caution 
in  making  sweeping  generalizations. 

In  wasps.  Von  Siebold l  conducted  investigations  with  the 
fertilized  and  with  the  unfertilized  ova  of  the  wasp,  Nematus 
ventricosus,  each  kind  of  which  produces  both  sexes  under 
certain  conditions. 

DEVELOPMENT  OF  FERTILIZED  OVA 


END  OF  LARVAL 
PERIOD 

NUMBER  OF  FEMALES 
TO  100  MALES 

END  OF  LARVAL 
PERIOD 

NUMBER  OF  FEMALES 
TO  loo  MALES 

Fifteenth  of  June  . 
Tulv 

M 

77 

August      .... 
End  of  August  . 

340 
SOO 

Tulv 

260 

September  .    .    . 

IOO 

DEVELOPMENT  OF  UNFERTILIZED  OVA 


From  this  we  conclude  that  in  general  fertilized  ova  produce 
females,  but  not  exclusively,  the  proportion  of  females  being  in 
some  accord  with  temperature  or  food,  or  both. 

Here  the  unferti- 
lized ova  produced 
males  except  when 
the  conditions  of  de- 
velopment were  so 
favorable  as  to 
shorten  the  larval 
period  to  the  utmost, 
leading  Geddes  and 
Thomson  to  remark 
that  even  "where 
the  production  of 
males  is  the  normal  condition,  favorable  environmental  influ- 
ences appear  to  introduce  females." 


NUMBER  OF 

DURATION  OF 

EXPERIMENT 

LARVAL  STATE 

II 

21  days 

All  males 

12 

19  days 

All  males 

J3 

1  8  days 

493  males,  2  females 

14 

17  days 

265  males,  2  females 

15 

17  days 

374  males,  8  females 

16 

1  8  days 

1  68  males,  i  female 

17 

24  days 

i  male 

1  Geddes  and  Thomson,  The  Evolution  of  Sex,  pp.  48,  49. 


634  PRACTICAL   PROBLEMS 

SECTION    IV  — SEX  IN   MAMMALS 

Temperature  and  nutrition  seem  to  be  controlling  factors  in 
many  of  the  lower  forms,  and  when  such  is  the  case  it  is  remark- 
able that  in  every  instance  the  production  of  females  seems  to 
accompany  the  more  favorable  conditions,  and  that  of  males 
the  harder  or  less  favorable. 

Among  mammals  there  is  little  experimental  evidence,  but 
that  little  points  to  the  same  general  fact  as  found  among  lower 
animals,  though  the  larger  animals  are  manifestly  less  directly 
influenced  by  surrounding  conditions.  Girou  divided  a  flock  of 
three  hundred  ewes  into  two  equal  lots,  one  of  which  was  ex- 
tremely well  fed.  This  lot  was  served  by  two  young  rams  ;  the 
other,  scantily  fed,  by  two  mature  ones.  The  well-fed  lot  (served 
by  young  rams)  produced  60  per  cent  females,  the  other  lot  only 
40  per  cent  females.1  The  difference  in  age  of  the  rams  intro- 
duces a  second  element,  but  the  facts,  if  true,  are  significant. 

This  is  about  all  that  is  known  of  this  phase  of  the  question. 
Experimental  evidence  seems  to  indicate  that  abundant  food, 
optimum  temperatures,  and  generally  favorable  conditions  tend 
to  the  production  of  females  ;  but  when  we  come  to  predict  the 
limits  to  which  the  rule  will  apply  we  must  proceed  with  great 
caution,  confessing  that  our  exact  knowledge  is  exceedingly 
limited. 

SECTION  V  — THE  " ACCESSORY  CHROMOSOME"   AND 
SEX  DETERMINATION2 

Certain  inequalities  between  germ  cells  in  respect  to  the  dis- 
tribution of  chromatin  matter  have  long  been  known.3 

1  Geddes  and  Thomson,  The  Evolution  of  Sex,  p.  51. 

2  Wilson  (1906),  "Studies  on  Chromosomes,  \\\"  Journal  of  Experimental 
Zoology,  III,  No.  i,  pp.  1-39.    Also  the  following  :   Beard,  The  Determination  of 
Sex;  Castle   (1903),  "The  Heredity  of  Sex,"  Bulletin  of  the  Museum  of  Com- 
parative Zoology,  XL,  4;  McClung   (1902),  "The  Accessory  Chromosome.     Sex- 
Determinant?"    Biological  Bulletin,  III,  i,  2;  Morgan  (1904),  "Self-Fertilization 
Induced  by  Artificial  Means,"  Journal  of  Experimental  Zoology,  I,  i  ;  Studies  in 
Spermatogenesis  with  Special  Reference  to  the  Accessory  Chromosome,  Publica- 
tion No.  36,  Carnegie  Institute,  Washington,  D.C.,  September,  1905 ;  Wilson,  "The 
Chromosomes  in  Relation  to  the  Determination  of  Sex  in  Insects,"  Science,  XX11, 
564,  October,  1905.  8  Wilson,  The  Cell,  pp.  271-272. 


THE   DETERMINATION   OF  SEX  635 

For  example,  Wilson  reports  that  as  long  ago  as  1891  Hen- 
king  "  discovered  that  in  the  second  spermatocyte  division  of 
Pyrrhocoris  one  of  the  chromosomes  passes  undivided  into  one 
of  the  daughter  cells  (spermatids),  which  receives  twelve  chro- 
matin  elements,  while  its  sister  receives  but  eleven"  ;  so  that, 
of  the  four  resulting  spermatozoa,  two  possess  an  additional 
chromosome  as  compared  with  the  other  two.1 

Other  discoveries  were  reported,  and  Paulmier  (1898,  1899), 
working  with  Anasa  in  Wilson's  laboratory,  found  that  in  the 
first  spermatocyte  division  eleven  tetrads  appeared,  one  of  which 
was  "  much  smaller  than  the  others  "  and  seemed  "  to  arise  from 
a  single  nucleolus-like  body  .  .  .  and  by  a  process  differing  con- 
siderably from  the  others."  He  adds  :  "  In  the  second  (and  last) 
spermatocyte  division  the  (ten)  larger  dyads  divide  to  form 
chromosomes  in  the  usual  manner ;  the  small  dyad,  however, 
fails  to  divide,  passing  over  bodily  into  one  of  the  spermatids. 
In  this  case,  therefore,  half  the  spermatids  receive  ten  single 
chromosomes,  while  the  remainder  receive  in  addition  a  small 
dyad."  2 

The  fact  was  gradually  established  that,  at  least  in  Hemiptera 
and  in  certain  other  insects,  one  of  the  chromatin  masses  of  the 
male  maturation  cell  differs  from  its  fellows,  and  undergoes  one 
less  division  than  they,  so  that,  of  the  group  of  four  spermatozoa 
arising  out  of  the  double  division  of  the  spermatocyte,  two  will 
possess  an  additional  chromosome  as  compared  with  the  other 
two.  This  additional  member  has  been  variously  named  by  dif- 
ferent experimenters,  the  terms  "  accessory  chromosome"  and 
"  heterotropic  chromosome"  being  the  most  common. 

Here  is  about  where  the  matter  rested  till  McClung  (1902) 
advanced  the  theory  that  the  accessory  chromosome  is  the  sex- 
determinant  t  assuming  (erroneously  as  we  now  believe)  that  if 
the  ovum  should  be  fertilized  by  one  of  the  spermatozoa  contain- 
ing the  accessory  chromosome  the  offspring  would  then  be 
provided  with  the  accessory  and  its  sex  would  therefore  be 
male ;  while  if  the  fertilization  should  be  by  one  of  the  sperma- 
tozoa destitute  of  the  accessory,  the  offspring  would  of  necessity 
be  of  the  opposite  sex. 

1  Wilson,  The  Cell,  p.  271.  2  Ibid.  p.  272. 


636  PRACTICAL  PROBLEMS 

This  view  of  the  case  made  it  appear  that  the  female  cells  cor- 
respond most  closely  with  those  spermatozoa  which  are  destitute 
of  the  accessory,  and  here  the  matter  stood  until  Montgomery 
(1904),  Gross  (1904),  and  Wallace  (1905)  discovered  that,  in  cer- 
tain species  at  least,  the  ovum  has  the  same  number  of  chromo- 
somes as  the  spermatozoa  with  the  accessory.  These  experimenters 
came  to  the  conclusion  that  "  only  one  of  the  two  classes  of  sper- 
matozoa is  functional,  namely,  that  in  which  the  heterotropic  (ac- 
cessory) chromosome  is  present.  Those  of  the  other  class  were 
assumed  to  degenerate,  after  the  fashion  of  polar  bodies."  l 

Wilson  (1906),  shows  that  "the  sexes  in  hemipters  of  this 
type  do  in  fact  show  a  constant  difference  in  the  number  of 
chromosomes."2  He  has  determined,  in  at  least  four  genera, 
that  the  number  of  chromosomes  in  the  female  cell  corresponds 
with  the  larger  number  in  the  male  cell;  in  other  words,  that  the 
"accessory  chromosome,"  though  present  in  but  half  the  sper- 
matozoa, is  found  in  all  female  germ  cells.  This  being  true,  the 
"  remarkable  "  spermatozoa  are  not  those  with  the  accessory, 
but,  on  the  contrary,  those  without  it,  and  they  are  to  be 
regarded  as  in  some  sense  deficient. 

Wilson  shows  conclusively  the  opposite  of  Gross'  and  Wallace's 
hypothesis,  namely,  that  when  a  female  cell  unites  with  a  sper- 
matozoon destitute  of  the  accessory  chromosome,  then  the 
accessory  of  the  ovum  finds  no  mate  and  a  male  develops  ;  and 
that,  on  the  other  hand,  if  the  ovum  happens  to  be  fertilized  by 
one  of  the  spermatozoa  provided  with  an  accessory,  then  each 
accessory  finds  its  mate,  there  is  then  no  solitary  accessory,  and 
a  female  results. 

Extending  his  experiments,  Wilson  finds  two  kinds  of  acces- 
sory chromosomes,  —  the  one  already  described,  which  is  smaller 
than  the  ordinary  chromosomes,  and  another  which  is  larger.  In 
this  connection  it  should  be  remarked  that  his  investigations 
show  great  differences  in  size  among  the  chromosomes  generally, 
but  that  the  "accessory"  can  readily  be  detected,  whether 
larger  or  smaller  than  the  others,  and  that  all  chromosomes, 
large  or  small,  —  except  the  accessory,  —  can  readily  be  assigned 
in  pairs  under  the  microscope. 

^  Journal  of  Experimental  Zoology,  III,  No.  I,  p.  2.  '2  Ibid. 


THE   DETERMINATION   OF  SEX  637 

It  should  be  said  in  this  connection,  too,  that  in  certain  species 
the  accessory  seems  always  present,  —  in  both  spermatozoa  as 
well  as  in  all  female  cells,  — but  that  when  this  is  the  case  the 
accessories  are  distinguished  by  some  kind  of  qualitative  differ- 
ence not  understood,  but  that  gives  to  two  of  the  spermatozoa 
of  each  group  of  four  a  different  character  from  the  other  two. 

If,  therefore,  it  shall  appear  that  all  female  cells,  after  extru- 
sion of  the  polar  bodies,  are  in  possession  of  this  accessory  chro- 
mosome, whatever  its  peculiar  quality,  and  if,  out  of  each  group 
of  four  spermatozoa  arising  from  a  single  spermatocyte,  two  are 
in  possession  and  two  are  destitute  of  this  accessory,  then  we 
have  in  the  spermatozoa  themselves  a  very  evident  fundamental 
cause  of  sex  determination,  and,  as  the  numbers  are  equal,  under 
the  law  of  chance  the  sexes  should  be  equal,  as  in  fact  they 
practically  are. 

Here  in  truth  would  seem  to  be  a  fundamental  cause  of  sex 
determination.  Whether  it  is  operative  in  all  forms  of  life  or  only 
in  certain  species,  it  is  yet  too  early  to  even  speculate.  A  fertile 
field  of  inquiry  is  here  opened  up,  and  the  near  future  may  be 
expected  to  afford  important  additional  data  on  this  most 
difficult  subject. 

Summary.  There  are  various  circumstances  that  appear  to 
influence  the  sex  of  offspring.  These  seem,  in  some  cases,  to  be 
connected  with  nutrition,  and,  in  others,  with  the  inherent  nature 
of  the  germ.  The  present  state  of  knowledge  is  insufficient  to 
solve  the  problem  of  sex  differentiation,  but  it  is  safe  to  say  that 
none  of  the  traditional  beliefs  are  warranted  by  the  known  facts. 


ADDITIONAL  REFERENCES 

CHANGING  SEX  IN  PLANTS.    Tropical  Agriculture,  1903,  pp.  789-790. 
CHROMOSOMES   IN   RELATION   TO   SEX   DETERMINATION    IN    INSECTS. 

By  E.  B.  Wilson.    Science,  XXII,  500-502. 
Do    SEEDLESS    FRUITS   REQUIRE   POLLINATION?    Experiment   Station 

Record,  XV,  1080. 

EXPERIMENTAL  ZOOLOGY.    By  T.  H.  Morgan.    Chapters  XXIV-XXVII. 
EXPERIMENTS   IN    HEREDITY    AND    SEX    DETERMINATION   IN  MOTHS. 

Report  of  the  British  Association  for  the  Advancement  of  Science, 

1904,  p.  594. 


638  PRACTICAL  PROBLEMS 

INFLUENCE  OF  NUTRITION  ON   SEX.    Experiment  Station  Record,  XVI, 

228. 
PARTHENOGENETIC    FERTILIZATION    IN    THE    HONEYBEE.     Experiment 

Station  Record,  XV,  792. 
RECENT  THEORIES  IN  REGARD  TO   DETERMINATION  OF  SEX.    By  T. 

H.  Morgan.    Popular  Science   Monthly,  LXIV,  97-1 16. 
SEX  CONTROL.    By  Professor  Schenck  of  Austria.    Science,  VII,  736- 

738. 
SEX  DETERMINATION  IN  BEES.    (A  discussion  of  the   Dzierzon-Dickel 

controversy.)    By  B.  Sporrer.    Experiment  Station  Record,  XI,  5$i, 

657,  956. 
SEX  DETERMINATION, — WHETHER  BUD  SHALL  BE  LEAF  OR  FLOWER. 

By  E.  S.  Goff.    American  Garden,  1901,  pp.  330-333,  346-347. 
SEX  IN  MICE.     By   Parsons  and  Copeman.     Proceedings  of    the    Royal 

Society,  London,  LXXIII,  32-48. 
SEX  IN  PLANTS   A   MATTER  OF   NUTRITION.    By   T.    Mehan.     Report, 

Department  of  Agriculture,  1898,  pp.  536-548;  Experiment  Station 

Record,  XI,  910. 
WISCONSIN   EXPERIMENT  STATION  REPORT,  1900,  pp.  266-285  ;  1901, 

pp.  304-316. 
ZIEGLER'S    THEORY    OF    SEX    DETERMINATION.     By   T.    H.    Morgan. 

Science,   XXII,    839-841. 


CHAPTER  XIX 

PLANT  BREEDING 

When  the  principles  of  breeding  are  once  understood,  their 
application  to  special  cases,  either  in  plant  or  animal  breeding, 
is  largely  a  matter  of  common  sense,  and  no  extended  discussion 
of  particular  operations  is  necessary. 

It  has  already  been  remarked  that  the  breeder  needs  the 
utmost  possible  familiarity  with  the  particular  line  he  hopes  to 
improve.  This  familiarity  he  will  get  largely  through  experience, 
but  he  cannot  afford  to  neglect  any  source  of  information  that 
will  enlarge  his  acquaintance  with  the  breed  or  the  variety,  for 
every  item  of  knowledge,  will  constitute  a  valuable  asset  in  his 
business  when  the  time  comes,  as  it  surely  will,  for  weighing 
slight  differences  in  the  balance  in  order  to  determine  questions 
of  selection.  This  involves  detail  which  only  the  practical 
breeder  can  acquire,  and  upon  which  attempted  instruction 
amounts  to  little  more  than  academic  dissertation.  Certain 
special  facts  and  principles,  however,  run  through  plant  breed- 
ing, as  distinct  from  animal  breeding,  and  these  it  is  well  to 
clearly  understand  in  advance  of  actual  operations. 

SECTION  I  — ADVANTAGES  AND  LIMITATIONS 

Advantages  in  plant  breeding.  The  plant  breeder  possesses  no 
less  than  six  distinct  advantages  as  compared  with  the  breeder 
of  animals  : 

1.  Large  numbers,  giving  excellent  opportunity  for  selection. 

2.  Rapid  reproducing  powers,  resulting  in  a  marvelous  saving 
of   time  as  compared  with   that   necessarily  consumed  in  the 
slower  process  of  animal  breeding. 

3.  The  relative  cheapness  of  individuals,  making  wholesale 
destruction  economically  possible. 

639 


640  PRACTICAL  PROBLEMS 

4.  The   greater  likelihood   of   mutations   arising  from  mere 
point  of  numbers,  if  from  no  other  cause,  and  the  greater  ease 
with  which  these  may  be  detected  if  they  do  arise. 

5.  The   greater  chance   of   preserving   mutations,   owing   to 
rapid  powers  of  reproduction. 

6.  The  possibility  of  reproducing  asexually  by  budding,  cut- 
ting, etc.,  which  overcomes  to  a  large  extent  the  disasters  of 
sterility  and  avoids  the  operation  of  Mendel's  law  in  the  propa- 
gation of  hybrids. 

The  plant  breeder,  therefore,  not  only  enjoys  superior  advan- 
tages in  selection,  but  he  is  free  to  make  full  use  of  mutations 
and  the  principle  of  crossing,  —  two  forms  of  improvement  all  but 
closed  to  the  animal  breeder.  Naturally,  therefore,  his  operations 
assume  one  of  three  well-defined  forms  or  systems  of  breeding  : 

1.  "  Straight  selection,"  or  breeding  from  the  best,  the  pur- 
pose being  the  improvement  of  existing  varieties  rather  than  the 
production  of  new  strains. 

2.  Maintaining  extensive  plantings  in  the  hope  of  detecting 
spontaneous  mutants,  the  object  being  the  production  of  new 
varieties. 

3.  Crossing,  or  hybridizing,  with  the  purpose  of  producing 
new  strains. 

New  strains  produced  by  either  the  second  or  the  third  method 
are  of  course  variable  and  capable  of  improvement  by  straight 
selection.  Each  system  of  breeding  requires  its  own  methods, 
suited  to  the  material  in  hand  and  the  character  of  the  improve- 
ment sought.  Some  species  do  best  with  one  system,  others 
with  another,  and  only  experience  can  decide  which  is  most 
prolific  of  results  in  a  particular  case.  The  first,  straight  selec- 
tion, is  the  safest,  and  is  always  certain  of  results ;  but  most 
specie::  respond  well  to  the  second  and  the  third,  which,  with 
suitable  material,  are  capable  of  the  richest  results  known  to  all 
breeding,  and  are  the  systems  par  excellence  for  the  production 
of  new  strains. 

Crossing  has  latterly  fallen  into  some  disrepute  because  of 
the  emphasis  laid  on  Mendel's  law,  and  the  principle  of  mutation 
is  but  recently  recognized ;  but  the  prediction  is  ventured  that 
the  former  w:ll  be  restored  to  favor  in  plant  breeding,  and  that 


PLANT  BREEDING  641 

mutation  will  yield  unexampled  results  in  certain  species  that  are 
"  in  the  mutable  state." 

Limitations  and  disadvantages  of  the  plant  breeder.  It  is  not 
all  clear  sailing  for  the  plant  breeder.  He  has  no  less  than  six 
distinct  limitations  which  he  must  recognize  in  advance  : 

1.  His  varieties  are  subject  to  the  effects  of  soil  and  climate 
in  a  way  quite  unknown  to  the  animal  breeder.    His  operations 
are,  therefore,  in  a  large  measure  local  rather  than  general  in 
their  results. 

2.  The    rapid    rate    of    reproduction    necessitates    wholesale 
destruction,  with  the  almost  certain  loss  of  "good  things." 

3.  It  is  impossible  to  prevent  accidental  crossing  of  many 
varieties  by  insects  and  by  the  wind. 

4.  It  is  difficult  to  keep  accurate  records. 

5.  The  product  is  cheap  and  it  can  be  readily  and  rapidly 
reproduced  by  every  novice  the  moment  it  is  on  the  market. 
This  necessitates  that  the  breeder  shall  operate  as  a  seedsman 
in  order  to  secure  financial  returns  for  his  labors,  or  else  that 
he  shall  sell  his  production  to  those  who  are  seedsmen. 

6.  The   extravagant    claims    often .  made    for   new   varieties 
possessing  little  or  no  merit  tend  to  destroy  confidence  in  new 
creations.    This  attitude  on  the  part  of  a  portion  of  the  trade 
leads  the  public  to  discount  heavily  even  the  moderate  state- 
ments of  reputable  seedsmen,  reducing  by  a  considerable  per- 
centage the  profits  of  the  business. 

Two  of  these  natural  limitations,  —  the  limitations  of  the  soil 
and  the  difficulty  of  keeping  accurate  records,  —  call  for  special 
attention. 

SECTION  II  — SOIL  AND  CULTURE  CONDITIONS 

The  breeder  is  all  but  powerless  to  alter  climate  conditions, 
but  the  fertility  of  the  land  is  absolutely  under  his  control. 
Should  the  soil  for  breeding  operations  be  rich  or  poor  ?  at, 
below,  or  above  the  average  of  that  upon  which  the  crop  is 
likely  to  be  grown  ? 

The  argument  is  often  advanced  that  if  breeding  operations 
be  carried  on  upon  land  below  the  average  of  fertility,  then  the 


642  PRACTICAL  PROBLEMS 

strain  will  prosper  even  better  in  the  hands  of  the  farmer,  and 
thereby  stand  more  chances  of  pleasing  when  put  to  the  actual 
test  on  the  farm  or  in  the  orchard.  Specious  but  faulty,  is  the 
only  correct  verdict  as  to  this  position,  though  it  may  be  main- 
tained, perhaps,  as  to  some  special  strains  particularly  sensi- 
tive to  high  fertility.  Improvement  is  what  is  aimed  at  by  the 
breeder,  —  the  production  of  better  strains  than  before.  On 
this  there  are  two  significant  points  : 

1.  The  breeder  will  not  know  when  he  has  succeeded  in  pro- 
ducing an  improvement  unless   the   soil   conditions   are  good 
enough  to  permit  full  and  complete  development. 

2.  All  experience  goes  to  show  that  plants  are  more  variable 
in  soils  of  high  fertility  than  in  soils  of  low  fertility.    This  is  the 
experience  of  De  Vries,  of  Darwin,  and,  so  far  as  is  known  to  the 
writer,  of  every  plant  breeder  upon  record. 

The  object  in  all  plant  breeding  is  the  production  of  improve- 
ment. This  is  partly  dependent  upon  fertility,  and,  in  general, 
plant-breeding  operations  will  be  most  successful  on  lands  of 
maximum  fertility.  Some  acclimatization  may  afterward  be 
necessary  as  to  soil  as  well  as  to  climate,  but  the  latter  is 
involved  in  all  plant  breeding, — and  the  former  too,  for  that 
matter,  —  for  no  soil  can  be  fairly  representative  of  any  very 
great  extent  of  territory. 

The  balance  of  fertility.  Much  remains  to  be  learned  as  to 
the  elements  that  should  predominate  in  a  fertile  soil.  In 
general,  nitrogen  favors  the  growth  of  leaf  and  stem,  but  there 
is  much  reason  to  believe  that  seed  formation  is  intimately 
related  to  the  supply  of  phosphorus.  The  botanist  will  tell  us 
that  Saprolegnia,  for  example,  grows  luxuriantly  in  beef  extract 
or  peptone,  but  produces  no  reproductive  organs  ;  grown  in 
nutrient  solutions  containing  abundance  of  phosphorus,  how- 
ever, reproductive  organs  form  readily,  especially  in  the  female. 

Without  doubt  much  remains  to  be  learned  in  the  matter  of 
making  up  of  soils  most  favorable  for  the  production  of  desirable 
variations  in  different  classes  of  plants.  In  this  matter  of  soil 
fertility  and  cultural  requirements  let  the  plant  breeder  provide 
maximum  conditions,  with  no  fear  of  evil  consequences.  If  he 
can  succeed  in  producing  a  desirable  variety  by  hook  or  by 


PLANT  BREEDING  643 

crook,   acclimatization  will   come  to  his  aid   and  help  him   to 
preserve  it. 

Of  one  fact  we  may  be  well  assured,  namely,  that  every  plant 
is  at  its  best  under  optimum  conditions.  That  is  the  time  when 
favorable  variations  may  be  most  confidently  expected  ;  in  other 
words,  that  is  the  time  when  it  will  respond  most  favorably  to 
selection.  The  writer  believes  this  to  be  the  general  principle 
from  which  to  work  out  the  conditions  under  which  the  particular 
strain  or  strains  yield  best  results,  but  the  plant  breeder  must 
not  deceive  himself  into  thinking  that  he  will  get  valuable  devi- 
ations from  type  while  the  plant  is  enduring  hard  conditions,  the 
effect  of  which  is  to  bring  everything  to  the  dead  level  of  medi- 
ocrity, where  little  improvement  is  possible  by  breeding  without 
first  improving  the  conditions  of  growth. 

SECTION  III  — SYSTEMS  OF  PLANTING 

In  general,  three  systems  of  planting  are  in  use  among  plant 
breeders : 

1.  The  nursery  system,  in  which  the  plants  are  treated  as 
individuals,  each  being  given  abundance  of  room,  and  each  made 
the  basis  of  selection  at  the  close  of  the  season. 

2.  The  field  system,  in  which  individual  plants  are  not  given 
special  opportunities.     Seed  is  saved  from  the  best  plants,  but 
no  attempt  is  made  to  identify  and  isolate  particular  parentage. 
This  is  "  improvement  "  rather  than  breeding,  and  is  in  common 
use  among  general  farmers. 

3.  What   Webber  calls    the   Burbank   method    of    crowding 
thousands  of  seedlings  close  together  on  good   soil   and  then 
selecting  the  few  that  are  able  to  endure  the  battle  and  survive. 

Each  system  has  its  advantages,  especially  the  first  and  third, 
but  the  third  merges  into  the  first  the  moment  that  really  close 
work  begins. 

All  things  considered,  it  is  altogether  likely  that  the  greater 
part  of  our  results  will  be  obtained  by  the  so-called  nursery 
method.  In  any  event  this  is  the  method  that  lends  itself  to 
the  best  grade  of  work  and  to  the  most  complete  records.  It  is 
the  one  therefore  that  will  receive  further  consideration  here. 


644  PRACTICAL  PROBLEMS 

Plot  or  row  in  the  nursery  system.  Shall  the  individuals  of  a 
single  selection  be  planted  together  in  rectangles  or  grown  in 
separate  rows  ?  Each  system  has  its  advocates,  and  the  matter 
is  to  be  decided  first  of  all  by  convenience  in  cultivation  and 
harvesting,  and  second  by  convenience  in  keeping  records.  The 
two  systems  are  well  illustrated  by  the  methods  employed  at 
the  two  experiment  stations  of  Minnesota  and  Illinois. 

The  plot  system.  This  system  is  best  described  by  its  use  at 
the  Minnesota  station,  where  it  has  been  fully  elaborated  and  is 
constantly  employed  for  all  breeding  work.1  Under  this  system 
as  there  employed  the  procedure  is  substantially  as  follows, 
taking  wheat  as  an  illustration.  When  a  new  variety  is  received 
or  a  promising  plant  is  selected  its  history  is  recorded  on  a 
record  sheet  5^  x  8^  inches  and  punched  at  the  end  for  filing. 
It  is  given  a  class  name  and  a  number  of  its  own  ("  Nursery 
Stock  No.  -  "),  and  if  it  sprang  from  a  numbered  stock,  that 
number  is  also  recorded  as  "  Parent  Stock  No.  — ."  This  sheet 
is  known  as  the  "  Introductory  Sheet,"  and  is  reproduced  here 
on  a  reduced  scale. 


Form  61 


SELECTED   STOCK— INTRODUCTORY  SHEET 


Nursery 

S::cx  N:. 


M/HPAT       Class  Name  of  Minn.  No.  of 

WHtAl  stock Parent  Stock.. 


Date- 
Origin  and  History  of  Parent  Stock 


The  seed  is  then  planted  by  itself  in  a  rectangular  plot,  ten 
plants  square  if  possible,  —  hence  known  as  a  "centgener 
plot."  Notes  are  taken  both  on  the  centgener  plot  as  a  whole 
and  on  individual  plants,  and  recorded  on  sheets  (see  table  on 
opposite  page,  reduced  size). 

1  See  BulUti*  Xo.  62,  Minnesota  Agricultural  Experiment  Station,  for  a  full 
description  of  the  plot  system  as  used  at  this  station. 


PLANT  BREEDING 


645 


YEARLY  HISTORY  SHEET 

WHEAT  Class  Name  Nursery  Stock  No  
From  Plant  No  /  Cent.  No  / 
CENTGENER  NOTES 

fc 

NIVHQ 

jo  aiaij^ 

AVVHig 

jo  QIHI^ 

NITROGEN 

1 

o 
z 

jj 

1 

1 

0 

3    -S 

jji 

AVERAGE 
Straw 

!i 

S 

<n 

No.  PLANTS 
HAR- 
VESTED 

o 

3 

£ 

< 

X 

o 

i* 

h 

b 

s 

0) 

3*! 

ri 

H  £  « 
S  B  £ 

«a* 

I,? 

2  o  us 
1      * 

STIFFNESS 

0 

3 

SPIKES 

If 

STRENGTH 

j: 

HEIGHT 

6 
K 

£ 

H 

SDNV 

-XSISH^  xsn^i 

.      SSHNHJIXg 

No.  SEEDS 
PLANTED 

XHOI3H 

M.1XV 

ONI 
JVSAVQ 

DATE 
PLANTED 

II 

II 

I 


646  PRACTICAL  PROBLEMS 

Manifestly  all  the  plants 
on  this  centgener  plot  have 
the  same  centgener  num- 
ber, but  any  promising 
plant  in  the  plot  may  be 
given  a  "  nursery  number  " 
at  any  time,  so  that  after 
the  system  is  well  started 
every  plant  has  two  num- 
bers, its  centgener  number 


and    its    nursery    number. 
From  these  original  records          Z 
three  other  sheets  are  made          Q£ 
up  as  a  kind  of  ledger  ac- 


three  other  sheets  are  made          cr.  6  ^  « 

*l  \ 

count  with  this  particular          UJ 
selection,  extending  per-          [_ 


§  g  £ 

**  < 


a 


haps    over    several    years.          g 
See  forms  65,  67,  and  68. 

The  system  seems  some- 
what  complicated  to  a  uj 
novice,  but  it  is  easily  and  ^ 
quickly  mastered  by  those  ^ 
engaged  in  the  work,  and  it  ^ 
is  applied  to  all  forms  of  <£ 
breeding  carried  on  at  the  |§ 
Minnesota  station.  ^ 

The   row  system.    This          ^  > 

system  is  best  illustrated 
by  its  use  at  the  Univer- 
sity of  Illinois,  where  it  is 
employed  not  only  for  corn 
breeding  but  also  for  wheat, 
oats,  and  other  plants.  The 
same  system  has  been 
adopted  by  the  Illinois  j> 
Seed  Corn  Breeders'  Asso- 
ciation, and  is  in  use  by  all  ^  » 
its  members. 


PLANT  BREEDING 


647 


.  ^  e 

o    Z    a 

^i 


p  2 

PH 


WHEAT  SUMMARY  SHEET  —  INDIVIDUAL  PLANT  NOTES 

Nursery  Stock  No  

NIVHQ 
dO   dlHI^ 

MVHXg  ' 

do  cnai^ 

a 

1 

BERRY 

•|    0    B 

i.    w 

Ij 

1) 
1 

0 

3 

H 

E 

s 
0 

• 

1,1 

ri 

H 

3 

z 

09 

'|.s 

bJO 

3 

6 

I 

SSHNdHIJ-S 

J.HOIHH 

OKIHnXVJ\[ 
SAVQ 

s  >^ 

648  PRACTICAL  PROBLEMS 

Under  this  system  each  ear  of  corn,  for  example,  is  planted 
in  a  separate  row,  and  as  many  rows  will  be  used  as  there  are 
ears  in  the  first  selection.  The  ear  in  the  book  and  the  row  in 
the  field  then  have  the  same  number. 

Suppose  we  are  starting  an  experiment  on  breeding  for  "  high 
oil."  It  is  the  first  year,  and  we  have  the  twenty  highest  oil 
ears  that  could  be  found  out  of  the  seed  at  hand.  These  ears 
will  be  numbered,  not  from  i  to  20,  but  from  101  to  120. 
Next  year  they  will  be  numbered  201  to  220,  or  225,  or  to  what- 
ever number  of  ears  may  be  available.  The  hundreds  always 
show  the  number  of  years  or  generations  of  improvement,  and 
the  rest  of  the  number  shows  the  field  number  of  the  ear  and  of 
the  row  in  which  it  is  planted.  Thus,  if  we  find  ear  No.  612, 
we  know  that  it  is  the  sixth  year  of  the  experiment,  or  the 
sixth  selection  from  the  original  stock,  and  that  it  is  planted  in 
row  No.  12  of  that  year's  field.  This  ear,  like  all  others  that 
have  been  analyzed,  has  its  laboratory  number,  or  "  annual  ear 
number,"  by  which  its  composition  may  be  traced ;  but  its 
"  pedigree  number,"  612,  for  example,  is  the  one  from  which 
its  breeding  is  traced.  A  sample  page  from  such  a  register 
book  shows  the  system  in  full,  there  being  no  other  records 
except  the  chemical  analyses.  This  is  the  entire  record  of  the 
high-oil  corn  for  1902.  (See  table  on  opposite  page.) 

Selecting  607  of  this  table,  for  example,  we  see  by  the  record 
that  its  dam  of  the  year  before  was  No.  504 ;  that  its  number 
in  the  chemical  laboratory  was  3923;  that  the  ear  was  6.5 
inches  long,  its  tip  circumference  4.8  inches,  and  its  butt  cir- 
cumference 5.8  inches;  that  it  had  12  rows,  and  that  each  row 
had  an  average  of  48  kernels ;  that  the  ear  weighed  5.3  ounces, 
and  had  7.13  per  cent  of  oil.  We  learn,  too,  that  it  was  planted 
in  row  No.  7,  which  was  71^$  hills  long  and  produced  85  pounds 
of  corn,  or  at  the  rate  of  63.5  bushels  per  acre;  that  there 
were  in  all  140  ears  of  corn  in  the  row,  the  average  oil  content 
of  which  was  6.65-1 

As  a  practical  detail  in  corn  breeding,  it  may  be  remarked 
that  the  best  ears  are  always  planted  in  the  middle  rows  to  give 
them  the  advantage  in  the  matter  of  pollination. 

1  As  determined  by  a  composite  sample  of  twenty  average  ears. 


PLANT  BREEDING 


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650  PRACTICAL  PROBLEMS 

As  between  the  two  systems  the  individual  must  take  his 
choice.  The  row  system  seems  to  have  the  advantage  of  sim- 
plicity, especially  for  plants  standing  in  cultivated  rows.  It  is 
the  one  most  readily  understood  and  most  easily  managed  by 
the  farmer,  but  either  is  easy  of  application. 

The  performance  record.  One  of  the  surprises  of  plant  breed- 
ing is  the  very  different  appearance  of  the  progeny  from  equally 
promising  individual  ears,  heads,  or  other  selection.  A  differ- 
ence of  two  to  one  is  not  at  all  uncommon,  and  not  infrequently 
a  row  or  centgener  plot  from  promising  seed  proves  almost 
worthless.  Hence  the  necessity  of  accurate  records  of  entire 
rows  and  centgener  plots.1  There  is  little  use  in  wasting  time 
on  inferior  material,  for  the  best  individual  plant  from  such  a 
fraternity  would  be  but  poor  stock  for  breeding  purposes.  All 
individual  selections  for  future  planting,  then,  should  be  made 
from  rows  (or  centgener  plots)  with  a  high  average  perform- 
ance record. 

Multiplying  plots  and  fields.  After  a  new  strain  has  proved 
satisfactory  in  the  nursery  row  or  plot,  it  must  needs  be  "  mul- 
tiplied "  in  order  to  secure  a  sufficient  quantity  for  sale.  It  is 
usually  customary  to  select  for  at  least  three  generations,  as  in 
the  production  of  sugar-beet  seed,  then  multiply  by  planting 
out  in  the  open  field  and  selling  the  total  crop  for  seed.  Thus 
the  beet  seed  of  the  market  is  generally  two  "removes"  from 
the  "  mother  beet,"  whose  selection  was  made  by  sugar  content. 

Seed  production  a  business.  It  is  fashionable  to  advise  the 
farmer  to  produce  his  own  seed.  From  the  standpoint  of 
acclimatization  it  is  good  advice,  but  from  any  other  standpoint 
it  is  bad  counsel,  providing,  of  course,  that  plant  breeders  and 
seedsmen  live  up  to  their  responsibilities. 

It  is  unthinkable  that  the  farmer  who  is  primarily  engaged  in 
production  can  also  be  a  skilled  improver  in  all  that  he  produces. 
He  may  breed  one  or  two  lines  of  animals  or  plants  himself, 
and  if  he  be  a  breeder  by  nature  and  training,  and  if  he  have 
the  leisure,  that  is  well ;  but  by  the  same  token  he  should 

1  The  row  of  the  row  system  corresponds,  of  course,  to  the  centgener  plot 
of  the  plot  system,  and  both  include  the  entire  progeny  of  an  "individual 
selection." 


PLANT  BREEDING  651 

expect  some  other  specialist  to  provide  him  with  his  foundation 
stock  in  other  lines.  No  man  living,  or  that  will  ever  be  born, 
will  succeed  in  breeding  all  lines  of  animals  and  plants,  except 
to  their  confusion  and  general  degradation. 

So  while  it  is  popular  to  advise  the  farmer  to  produce  his 
own  seeds,  it  is  better  business  policy  for  him  to  buy,  and  spend 
a  little  time  and  patience  in  acclimating  the  strains  if  need  be 
for  a  year  or  two,  before  putting  the  new  stock  into  common  use. 
This  will  generally  suffice,  and  if,  in  a  special  case,  as  perhaps 
in  corn,  no  improved  variety  will  successfully  acclimate,  then 
there  is  nothing  to  be  done  but  to  set  about  the  production  of 
an  improved  strain  of  the  local  variety ;  but  this  can  be  accom- 
plished by  a  few  persons  or  even  by'  one  person  as  well  as  it 
would  be  done  if  every  neighbor  undertook  the  task. 

Improvement,  even  in  plants,  is  costly  business,  and  when 
once  it  is  effected  a  real  investment  has  been  made  that  can  be 
multiplied  as  often  as  men  and  lands  are  available. 

The  interests  of  agriculture  demand  that  some  men  give  their 
time  and  genius  to  the  improvement  of  animals  and  plants. 
Their  number,  however,  will  never  be  relatively  large,  and  it 
need  not  be.  It  is  expedient  that  all  farmers  address  themselves 
to  the  serious  business  of  learning  how  to  handle  and  produce 
on  a  commercial  scale  the  really  excellent  creations  in  plant  and 
animal  life  that  the  genius  of  breeders  is  able  to  originate. 


ADDITIONAL  REFERENCES       . 

ABSTRACT  OF  PAPERS  READ  AT  THE  NEW  YORK  CONFERENCE  OF  PLANT 
AND  ANIMAL  BREEDERS  (September  3o-October  2,  1902).  Experi- 
ment Station  Record,  XIV,  208-222. 

BIBLIOGRAPHY.  (A  reference  to  forty-eight  articles  on  plant  breeding.) 
Experiment  Station  Record,  XV,  770 ;  also  in  Experiment  Station 
Record,  XVI,  354,  thirty-one  articles. 

BREEDING  ANIMALS  AND  PLANTS.  By  W.  M.  Hays.  Breeders'  Gazette, 
XLI,  892,944. 

BREEDING  CORN.  By  C.  P.  Hartley.  Year  Book,  United  States  Depart- 
ment of  Agriculture,  1902,  p.  539. 

BREEDING  COTTON.  By  H.  J.  Webber.  Year  Book,  United  States  Depart- 
ment of  Agriculture,  1902,  p.  365. 

BREEDING  FOR  EARLINESS,    Experiment  Station  Record,  X,  352. 


652  PRACTICAL  PROBLEMS 

BREEDING  PEANUTS.  North  Carolina  Experiment  Station,  Bulletin  No. 
168,  pp.  421-434  ;  also  in  Experiment  Station  Record,  XI,  1032. 

BREEDING  WHEAT.  By  William  Saunders.  Agricultural  Science,  1899, 
74-87;  also  in  Experiment  Station  Record,  XII,  339. 

BREEDING  WORK  OF  THE  MINNESOTA  EXPERIMENT  STATION.  By 
W.  M.  Hays.  Breeders'  Gazette,  XLIV,  1187. 

COFFEE  HYBRID.    Gardener's  Chronicle,  1899,  p.  240. 

COOPERATIVE  BREEDING.    By  W.  M.  Hays.    Breeders'  Gazette,  XLV,  14. 

CROSS,  MAIZE-TEOSINTE.  By  J.  W.  Harshberger.  Garden  and  Forest, 
1896,  p.  522  ;  also  in  Experiment  Station  Record,  VIII,  563. 

CROSS-BREEDING  OF  FRUITS.  (Summary  of  series  of  experiments  cover- 
ing a  number  of  years.)  By  J.  L.  Budd.  Iowa  Horticultural  Society, 
1900,  pp.  176-178;  also  in  Experiment  Station  Record,  XIII,  454. 

CROSSING  OF  PEAS,  BEANS,  ETC.    Experiment  Station  Record,  XVI,  263. 

CROSSING  STRAWBERRIES.  By  F.  W.  Card  and  G.  E.  Adams.  Rhode 
Island  Experiment  Station  Report,  1900,  pp.  247-267;  also  in  Experi- 
ment Station  Record,  XII,  944. 

CROSSING  VARIETIES.  By  B.  D.  Halsted.  New  Jersey  Experiment  Sta- 
tion Report,  1901,  pp.  389-411;  also  in  Experiment  Station  Record, 
XIV,  568. 

DIFFERENCE  IN  PLANT  AND  ANIMAL  BREEDING.  By  W.  M.  Hays. 
Breeders'  Gazette,  XLIV,  1132. 

EFFECT  OF  SOIL  ON  DEVELOPMENT.    Experiment  Station  Record,  XVI,  22. 

EXPERIMENTS  IN  PLANT  BREEDING  ON  THE  DOMINION  EXPERIMENTAL 
FARMS.  By  William  Saunders.  Transactions  of  the  Royal  Society 
of  Canada,  1902,  p.  115. 

EXPERIMENTS  OF  LUTHER  BURBANK.  By  David  Starr  Jordan.  Popular 
Science  Monthly,  LXVI,  201-225. 

GERMAN  METHOD  OF  BREEDING  SUGAR  BEETS.  Experiment  Station 
Record,  XIII,  642-948. 

HYBRID,  BLACKBERRY-RASPBERRY.  Experiment  Station  Record,  VII, 
36,  306. 

HYBRID  CORN.  By  C.  P.  Hartley.  Year  Book,  United  States  Department 
of  Agriculture,  1902,  pp.  539-550. 

HYBRID  TOMATOES.    Experiment  Station  Record,  XIII,  348. 

HYBRIDIZATION.  (Lists  of  hybrids  and  general  laws  of  heredity.)  By 
F.  A.  Waugh,  American  Garden,  1899,  No.  234,  p.  431. 

HYBRIDIZATION.  Papers  by  Bateson,  DeVries,  Bailey,  and  Webber. 
Science,  X,  1 13-116. 

HYBRIDIZATION  IN  BEANS.  By  R.  A.  Emerson.  Nebraska  Experiment 
Station  Report,  1903,  pp.  33-68  ;  also  in  Experiment  Station  Record, 
XVI,  563-564- 

HYBRIDIZATION  OF  BARLEY,  WHEAT,  OATS,  AND  FRUITS.  By  William 
Saunders.  Transactions  of  the  Royal  Society  of  Canada,  1894, 
pp.  139-142;  also  in  Experiment  Station  Record,  VII,  273-275. 


PLANT  BREEDING 


653 


HYBRIDIZATION  OF  CEREALS.    By  J.  H.  Wilson.    Report  of  the  British 

Association  for  the  Advancement  of  Science,  1904,  p.  796. 
HYBRIDIZATION  OF  RYE.    By  P.  Nielson.    Experiment  Station  Record, 

VII,  204. 

HYBRIDIZING  ROSES  AND  GOOSEBERRIES.    By  J.  L.  Budd.  Iowa  Experi- 
ment  Station   Bulletin  No.  36,  p.  868  ;  also  in  Experiment  Station 

Report,  X,  47. 
METHODS    OF    PLANTING   AND  SYSTEMS  OF   KEEPING   RECORDS.     By 

VV.  M.  Hays.    Breeders'  Gazette,  XLII,  10,  42,  124,  255. 
PHILOSOPHY    AND    PRACTICE    OF    BREEDING.      By    Luther    Burbank. 

Popular  Science  Monthly,  1905,  pp.  201-225. 
PROFITABLE  BREEDING  BY  IMPROVING  EXISTING  VARIETIES.   By  L.  H. 

Bailey.    Year  Book,  United  States  Department  of  Agriculture,  1896, 

pp.  297-304. 
REVERSION  AND  GRAFT  HYBRIDIZATION.    By  H.  J.  Webber.    Science, 

1896,  No.  92,  pp.  498-500. 
STRAWBERRY  BREEDING.     By  N.  O.  Booth.     American  Garden,   1900, 

p.  534  ;  also  in  Experiment  Station  Record,  XII,  246. 
USE  OF    IMMATURE    SEED   GIVES    INFERIOR   TREES.    By  T.    Christy. 

Gardener's  Chronicle,  1896,  p.  145  ;  also  in  Experiment  Station  Record, 

VII,  588, 


CHAPTER  XX 

ANIMAL  BREEDING 
SECTION  I  — ADVANTAGES  AND  DISADVANTAGES 

Advantages.  Animal  breeding  possesses  three  substantial 
advantages  over  plant  breeding  : 

1.  More  freedom  from  climatic  and  other  local  conditions,  so 
that  the  product  is  fitted  for  a  wider  range  of  service. 

2.  Relatively  good  prices,  because  the  individual  has  a  high 
value  and  is  not  so  easily  or  so  rapidly  multiplied. 

3.  Involving  superior  beings,  animal  breeding  becomes  one  of 
the  highest  forms  of  art.    In  this  we  are  dealing  not  only  with 
superb  physical  form,  but  with  mental  qualities  as  well,  and  here 
the  breeder  may  come  into  sympathetic  personal  relations  with  the 
products  of  his  hand  and  of  his  genius.    The  same  sympathetic 
relation  will  be  claimed  by  the  lover  of  plants,  and  especially  by 
the  lover  of  flowers  ;  but  the  fact  remains  that  only  with  animals 
do  we  find  consciousness  and  intelligent  response  to  our  moods 
and  passions.    What  feeling  on  earth,  outside  of  human  affection, 
can  approach  the  attachment  existing  between  a  man  and  his 
horse,  or  between  a  dog  and  his  master  ? 

Disadvantages.  But  the  animal  breeder  must  face  a  long  line 
of  limitations  and  disadvantages.  Some  of  these  can  be  easily 
singled  out  and  stated,  others  are  too  subtle  for  putting  into 
words  : 

1.  Numbers  are  necessarily  few,  and  reproduction  is  relatively 
slow,  making  selection  difficult  from  mere  scarcity  of  material. 

2.  Individuals  are  costly,  and  those  of  high  breeding  powers 
extremely  so.    This  makes  really  good  breeding  not  only  ex- 
pensive  but   in  a  measure  hazardous,  for  prices  have  a  way 
of    taking    a    sudden    drop,  often    with    little    or    no    warning 
when  nothing  better  than  the  open  market  affords  an  outlet 
for  surplus  stock. 

654 


ANIMAL  BREEDING  655 

3.  The  characters  to  be  selected  and  bred  for  are  generally 
not  few  but  many,  and  difficulties  in  selection  necessarily  increase 
out  of  all  proportion  to  the  number  of  points  to  be  attained. 

4.  As  if  the  breeder  did  not  have  troubles  enough  of  his  own, 
fashion  is.  continually  adding  points  that  demand  his  attention 
most  imperiously,  even  at  the  expense  of  better  things. 

5.  Animals   propagate  but  slowly,  and   breeding  operations 
necessarily  extend  over  many  years  and  several  generations  ;  the 
population  cannot,  therefore,  be  spread  out  to  view,  and  there  is 
more  or  less  uncertainty  as  to  actual  family  history  and  individ- 
ual merit,  —  all  of  which  makes  selection  more  or  less  difficult 
and  uncertain. 

6.  The  young  of  most  animals  are  promising,  but  selection 
cannot  safely  be  made  at  extreme  immaturity,  for  the  differ- 
ences between  inferiority  and  superiority  are  brought  out  only  in 
the  development  that  comes  with  full  maturity.    The  excellence  of 
breeding  is  mainly  shown  in  the  capacity  for  development,  and 
this   cannot  be  foretold  except  as  it   may  be   predicted  by  a 
general  knowledge  of  the   particular  family  line  and  the  spe- 
cial blood  combination  involved.    Some  of  the  most  promising 
"young  things"  are  the  bitterest  disappointment. 

7.  Animals  are   difficult  of  development,  and  many  of  the 
best-bred  things  are  never  properly  developed. 

8.  Animals  do  not  reproduce  asexually,  and  their  successful 
production  is  conditioned  upon  high  sexual  fertility.    Now,  imper- 
fect sexual  development  is  one  of  the  most  common,  if  not  the 
most  common,  defect  in  both  plants  and  animals.    Plants  may  be 
propagated  by  buds  or  cuttings,  but  animals  are  at  the  mercy  of 
sexual  reproduction.    In  nature  the  existing  lines  are  kept  at 
least  fairly  fertile  by  natural  selection,  but  in  domestication  no 
such  controlling  influence  exists  unless  supplied  by  the  breeder 
himself.    This  lack  he  must  provide  for  if  he  hopes  to  succeed, 
but  it  constitutes  one  of  his  principal  difficulties. 

9.  Fashion  and  custom  decree  that  animals  shown  at  the  fairs 
shall  be  put  into  extreme  condition,  and  this  is  a  constant  menace 
to  the  efficiency  of  a  breeding  herd. 

10.  A  strong  vein  of  speculation  has  entered  into  many  lines 
of  animal  breeding,  the  tendency  of  which  is  to  unsettle  prices 


656  PRACTICAL  PROBLEMS 

and  conditions  generally  in  what  ought  to  be  one  of  the  most 
steadily  conducted  of  all  the  industries. 

These,  in  brief,  are  some  of  the  limitations  of  the  animal 
breeder.  He  cannot  afford  to  close  his  eyes  to  their  existence, 
for  they  are  realities.  He  will  get  on  best  to  frankly  confess  their 
existence  and  to  meet  them  to  the  best  of  his  ability.  It  remains 
to  examine  a  little  more  closely  into  some  of  these  and  other 
detailed  considerations  that  must  engage  the  breeder's  attention. 


SECTION   II  — FEWER  CHARACTERS  FOR  SELECTION 

The  greatest  single  improvement  possible  in  present-day 
animal  breeding  in  most  lines  would  be  to  free  the  situation 
from  unimportant  characters.  At  best  the  breeder  must  pay 
regard  to  a  large  number  of  considerations  in  making  selections. 
Constitutional  vigor,  high  productive  powers,  and  utility  for  the 
purpose  in  mind  are  fundamental  considerations,  and  the  last 
(utility)  is  more  than  likely  to  cover  many  points. 

Now  the  difficulties  of  selection  increase  at  a  surprising  rate 
as  requirements  multiply.  If  a  proper  degree  of  constitutional 
vigor  is  found  in  but  one  animal  out  of  two,  —  and  it  is  not 
higher  than  that,  —  then  the  chances  of  a  particular  animal  prov- 
ing satisfactory  in  this  respect  are  but  one  out  of  two,  or,  as  we 
say,  his  probability  is  J.  If,  again,  but  one  animal  out  of  three 
is  fully  fertile,1  —  and  it  is  doubtful  if  the  proportion  is  higher, 
in  certain  lines  at  least,  —  then  the  chances  of  a  strong  constitu- 
tion and  full  fertility  being  found  in  the  same  animal  are  but 
\  X  J,  or  l.  If,  now,  we  add  to  this  a  third  requirement  found, 
say,  in  but  one  animal  out  of  ten,  then  our  chances  have  been 
reduced  to  \  X  \  X  -^  —  g\,  which  is  equivalent  to  saying  that 
only  one  animal  in  60  taken  at  random  —  that  is,  but  one  animal 
in  60  of  all  that  are  born  into  the  breed  —  will  fully  meet  our 
demands  and  satisfy  our  requirements,  except  in  so  far  as  the 
characters  in  question  may  be  related  by  causation  and  to  that 
extent  overlap. 

1  By  full  fertility  is  not  meant  the  power  to  reproduce  as  against  absolute 
barrenness,  but  rather  full  and  maximum  powers  of  reproduction,  —  that  is,  regular 
breeding  throughout  a  reasonably  long  life. 


ANIMAL  BREEDING  657 

If,  now,  to  this  we  add,  say,  three  other  requirements  ("points") 
represented  respectively  by  J-,  J^,  and  ^,  we  have  reduced  our 
chances  to  \  x  ^  X  T^  X  \  X  ^  X  ^,  or  1 1 5,200,  —  meaning 
that  not  one  individual  in  100,000  will  meet  our  demands.  But 
this  is  beyond  the  range  of  practical  selection,  and  it  means  that 
defects  will  of  necessity  be  accepted.  If  the  same  defect  were 
always  accepted  the  damage  would  be  less,  but  in  practice  one 
point  is  now  waived  and  then  another,  as  we  choose  the  least 
of  two  evils,  and  so  defects  linger  and,  behaving  according  to 
the  principles  of  Mendel's  law,  return  to  plague  us  long  after 
we  supposed  ourselves  through  with  them  and  well  freed  from 
their  influence.  This  is  really  mixed  breeding,  however  pure 
the  pedigree. 

Now  the  principle  is  this  :  we  should  tolerate  no  more  points 
at  any  one  time  than  can  all  be  found  in  the  same  individuals. 
When  the  entire  population  come  to  possess  these  few  charac- 
ters in  a  high  degree,  then  other  requirements  can  be  safely 
added,  because  the  breeding  for  a  few  characters  at  a  time 
amounts  to  practical  certainty.  The  breeds  with  which  this 
method  has  been  practiced  —  racing  horses  and  hunting  dogs, 
for  example  —  have  outstripped  anything  known  in  the  rapidity 
of  their  improvement,  and,  moreover,  a  foundation  has  been  se- 
cured on  which  other  requirements  may  safely  be  laid  ;  whereas 
the  breeds  in  which  many  requirements  have  been  exacted  con- 
temporaneously have  had  a  checkered  history,  full  of  ups  and 
downs,  and  the  end  is  not  yet, — nor  will  the  end  be  in  sight 
until  the  custom  is  abandoned  of  requiring  at  the  same  time  so 
many  points  as  to  put  the  matter  beyond  the  range  of  practical 
selection. 

The  direct  effect  of  too  many  points  of  selection  is,  first, 
temptation  to  overlook,  under  the  stress  of  circumstances,  those 
fundamental  biological  requirements,  —  constitution  and  high 
breeding  powers ;  and  history  shows  that  this  has  been  repeat- 
edly done,  to  the  extinction  of  some  of  our  otherwise  most 
promising  creations.  When  this  result  does  not  follow,  the 
inevitable  consequence  of  too  many  points  of  selection  is  that 
we  are  forced  to  accept  defects,  now  one  and  then  another,  as 
has  been  shown,  until,  under  Mendel's  law,  the  breed  becomes 


i 


658  PRACTICAL   PROBLEMS 

at  best  a  mixture  of  good  and  evil, — a  mixture,  moreover,  that 
will  never  purify  itself,  and  that  can  be  purified  only  by  a  return 
to  first  principles. 


SECTION   III  — FASHION 

As  fashion  decrees  the  cut  of  our  clothes,  so  it  also  decrees 
the  length  of  the  tail  of  a  cow  or  the  shape  of  her  horn,  and  the 
height  at  which  a  horse  should  raise  his  feet  from  the  ground. 
If  fashion  would  be  reasonable,  and  consistent,  and  stable,  it 
would  not  be  so  bad,  for  breeders  could  finally  adjust  themselves 
to  its  demands ;  but  it  is  not  stable,  and  often  it  is  neither 
reasonable  nor  consistent. 

Now  it  is  not  so  easy  to  change  the  conformation  of  an  animal 
as  it  is  to  alter  the  cut  of  a  garment,  which  means  at  the  most 
only  a  turn  of  the  shears  this  way  or  that.  Every  one  of  these 
decrees  of  fashion  indicates  an  additional  requirement  for  selec- 
tion, and  we  know  what  that  means  to  the  breeder;  not  only 
that,  but  such  decrees  are  certain  to  be  short-lived,  changing  for 
others  more  or  less  troublesome.  Worst  of  all,  many  of  these 
requirements  of  fashion  are  to  the  distinct  and  permanent  dis- 
advantage of  the  breed  —  that  is,  permanent  until  bred  out, 
which  we  have  learned  requires  approximately  six  generations 
of  successful  selection. 

But  the  mandates  of  fashion  are  to  be  reckoned  with,  erratic 
and  troublesome  though  they  may  be,  for  in  a  very  large  measure 
they  determine  sales  and  fix  pv  ices.  Now  the  breeder  is  in  the 
business  for  money,  and  he  must  sell  stock  or  abandon  all  hope 
of  profit,  —  which  in  the  end  means  to  abandon  the  enterprise 
entirely  ~  and  no  phase  of  practical  breeding  calls  for  more  wis- 
dom and  shrewdness  than  this  particular  problem, — how  to 
meet  the  changing  demands  of  the  market  and  keep  the  herd  or 
stud  intact  and  if  possible  improving. 

In  so  far  as  these  fashions  emanate  from  the  open  market 
their  control  is  practically  beyond  the  breeder.  But  some  of  the 
worst  of  them  emanate  from  among  the  breeders  themselves,  who 
sometimes  seem  bent  on  inventing  artificial  issues  on  which  to 
make  sales.  Sometimes  there  comes  a  feeling,  apparently,  that 


ANIMAL  BREEDING  659 

there  are  too  many  animals  of  a  given  breed  available,  and  that, 
in  self-protection,  new  standards  must  be  set  up. 

This  is  confusing  to  the  buyer  and  only  hurtful  to  the  breed- 
As  a  matter  of  fact,  there  never  were  and  never  can  be  too  many 
really  excellent  animals  of  any  breed.  The  question  of  develop- 
ing the  market  for  pure-bred  stuff  will  be  discussed  later,  but  here 
it  is  enough  to  say  that  no  artificial  standards  should  be  tolerated 
in  any  breed  merely  to  create  sales.  This  matter  can  be  con- 
trolled by  the  breeders  themselves  in  their  own  associations,  and 
when  it  is  controlled  a  large  share  of  the  senseless  and  disturbing 
"decrees  of  fashion"  will  have  disappeared  and  the  remaining 
ones  will  have  been  mostly  modified  into  comparative  harmless- 
ness.  There  is  too  much  homemade  law  passing  from  mouth  to 
mouth  among  breeders,  without  the  sanction  of  associations,  and 
much  of  it  would  never  be  seriously  supported  on  any  floor  if  the 
advocates  were  really  required  to  seriously  defend  it.  Here  is  a 
duty  that  every  association  owes  the  breed  it  advocates  and 
whose  interests  it  maintains. 

But  when  all  is  said  and  done,  how  shall  the  individual  proceed  to 
meet  the  decrees  of  a  craze  that  in  his  judgment  will  speedily  pass  ? 

There  is  no  better  way  than  by  the  use  of  sires  that  strongly 
possess  the  points  demanded  in  the  market,  always  being  care- 
ful to  preserve  a  goodly  number  of  the  best  females  uncontami- 
nated  from  the  infection.  These  will  form  the  nucleus  of  the 
new  herd  or  stud  after  the  craze  has  passed  and  the  pendulum 
has  swung  back  to  the  normal. 

Here  the  breeder  must  be  wise  in  his  judgment  as  to  whether 
a  new  thing  is  only  a  passing  craze  or  is  really  a  permanent 
improvement  in  the  breed,  and  here  his  accumulated  knowledge 
of  animals  will  serve  him  well;  but  he  should  be  well  advised 
that  by  the  proper  use  of  the  sire  a  herd  may  be  made  to  turn 
out  a  new  style  of  animal  for  a  considerable  time  without  in  any 
way  affecting  the  real  character  of  the  foundation,  and  this  can  be 
continued  as  long  as  the  old  stock  of  females  lasts.  As  the  time 
of  their  end  approaches,  however,  something  must  be  done  to 
restore  their  number,  or  else  the  new  point  must  be  accepted  and 
bred  into  the  females  which  really  constitute  the  backbone  of 
every  producing  herd. 


660  PRACTICAL  PROBLEMS 

SECTION   IV  — SHOW-RING  CONSEQUENCES 

Animals  that  have  made  their  record  in  the  show  ring  are 
none  the  worse  for  that  fact,  and  this  success  adds  greatly  to 
their  credit  as  individuals  and  to  the  commercial  value  of  their 
get  afterward.  Although  the  excessive  fitting  required  in  the 
ring  is  often  injurious,  it. is  not  necessarily  so.  It  is  of  course 
true  that  no  animal  will  remain  long  in  "  form,"  nor  can  the 
process  of  fitting  be  repeated  many  times.  Show-ring  animals 
are  thus  often  a  disappointment  to  the  eye  later  on,  but  this  is 
no  detriment  to  their  breeding  powers.  The  only  danger  from 
excessive  fitting  is  its  effect  upon  fertility,  and  if  this  has  been 
impaired  it  will  very  soon  become  evident. 

It  is  a  serious  question  as  to  when  a  breeder  can  afford  to 
take  the  risk  of  putting  into  the  ring  a  valuable  breeding  animal. 
As  a  matter  of  fact,  if  not  of  necessity,  most  show  animals  are 
young.  The  writer  does  not  share  the  opinion  that  show-ring 
animals  have  necessarily  been  injured  for  breeding  purposes,  any 
more  than  he  shares  the  opinion  that  show-ring  success  is  a 
guaranty  of  breeding  powers.  Upon  this  point  nothing  is  reli- 
able but  the  actual  test. 


SECTION  V  — TESTING  OF  SIRES  AND  DAMS 

When  we  remember  that  variability  cannot  be  reduced  below 
89  or  90  per  cent  of  the  variability  of  the  race,  or,  in  extreme 
cases,  perhaps  to  85  per  cent,  and  when  we  appreciate  the  fact 
that  no  matter  how  much  the  type  (or  mean)  has  been  improved 
the  variability  remains,  then  we  are  no  longer  surprised  at  the  large 
number  of  mediocre  individuals  that  appear  even  in  blood  lines 
the  most  aristocratic  and  that  have  been  longest  "  in  the  purple." 

The  necessity  for  selection,  therefore,  will  always  exist,  and 
when  we  add  to  this  that  other  fact,  that  many  mediocTe-foe&itg 
animals  are  after  all  great  breeders  and  many  exceptional  individ- 
uals bitter  disappointments,  there  is  an  additional  reason  for 
the  actual  test. 

And  still  again,  no  one  knows  positively  what  will  be  the 
result  of  a  new  combination  of  blood  lines  until  it  has  been 


ANIMAL  BREEDING  66 1 

tried ;  thus,  by  every  count,  we  arrive  at  the  conclusion  that 
real  progress  is  assured  only  with  tested  animals. 

Testing  dams.  The  test  of  a  dam  is  what  she  has  produced. 
If  the  herd  has  been  bred  by  the  owner,  —  and  in  general  no 
other  course  is  consistent,  —  then  the  records  of  the  herd  will 
show  the  breeding  powers  of  every  female  in  it,  and  any  one 
that  is  not  satisfactory  should  be  promptly  eliminated.  If  this 
course  is  pursued,  then  at  any  given  moment  the  owner  of  an 
established  herd  will  be  in  possession  of  a  tested  herd,  so  far  as 
the  females  are  concerned,  and  the  only  additional  testing  is  of 
each  new  sire  that  is  brought  into  service.1 

This  is  a  comparatively  simple  matter  if  the  breeding  powers 
of  the  female  side  of  the  herd  are  well  known.  If  they  are  not 
well  known,  the  breeder  is  worse  off  than  the  ship  at  sea  without 
rudder  or  compass ;  he  may  multiply  animals,  but  he  will  never 
do  much  real  breeding.  If  a  female  is  brought  into  the  herd,  she 
should  on  all  accounts  be  brought  in  on  her  breeding  record  if 
possible  ;  for,  of  a  hundred  females,  only  a  few  will  prove  great 
mothers  or  even  good  mothers.  If,  of  necessity,  young  females 
are  put  into  the  herd,  then  they  must  be  regarded,  like  the  regu- 
lar produce  of  the  herd,  as  under  a  test  until  each  shall  prove 
herself  a  breeder  entitled  to  a  place  in  the  permanent  herd. 

Testing  young  females.  This  is  a  job  that  the  breeder  has 
always  at  hand.  His  herd  is  short-lived  at  the  best,  and  however 
good  it  may  be  it  will  become  extinct  by  death  in  a  few  years 
unless  reenforced  from  younger  stock. 

While  individuals  live  many  years,  it  is  found  in  actual  prac- 
tice that  the  character  of  the  entire  herd  will  change  in  five 
years  with  cattle  and  horses,  and  in  much  less  time  with  sheep 
and  swine,  unless  properly  reenforced  with  young  animals.  A 
breeding  herd  is  a  moving  tide  of  life,  and  what  the  breeder 
does  he  must  do  quickly.  He  must  reenforce  the  stream  while 
it  is  at  the  flood.  He  must  keep  the  number  high  by  con- 
tinual reinforcement  and  not  wait  till  the  herd  is  shrinking  on 
his  hands. 

1  It  is  needless  to  remark  that  many  breeders  have  not  yet  learned  the  prin- 
ciple of  maintaining  their  own  stock  of  females ;  indeed,  a  good  number  confess 
to  buying  females  to  "  keep  up  the  herd." 


662  PRACTICAL   PROBLEMS 

* 

The  testing  of  young  females  is  a  difficult  business.  There 
is  little  use  in  breeding  them  to  unknown  sires,  whose  own  breed- 
ing powers  are  problematical.  To  do  that  is  to  measure  one 
yardstick  with  another  whose  standard  of  accuracy  is  unknown. 
The  young  females  should  be  bred  whenever  possible  to  tested 
sires,  and  then  the  breeder  will  have  an  accurate  measure  of 
what  they  should  be  expected  to  do  under  herd  conditions. 

Unity  of  the  herd.  The  old  plan  of  having  represented  in  the 
same  herd  all  fashionable  families  in  the  person  of  its  females  is 
fortunately  passing.  Such  a  herd,  no  matter  how  excellent  or 
well  bred  its  individuals,  was  after  all  but  a  motley  collection 
of  strongly  bred  differences,  on  which  no  sire  ever  born  could 
be  expected  to  succeed.  Such  attempts  have  involved  many 
breeders  in  a  hopeless  tangle  of  Mendelism,  for  these  violent 
admixtures  of  family  lines  amount  to  little  else  than  crossing, 
either  in  theory  or  in  practice. 

The  individual  breeder  succeeds  best  who  attempts  to  do  a 
distinctive  thing,  and  who  preserves  one  type  throughout  his 
collection  of  females,  which  is  his  herd.  He  will  find  this  diffi. 
cult  enough  to  accomplish  without  seeking  the  multiplication 
of  types  ;  and  he  will,  if  he  is  wise,  discard  many  females  in  the 
testing,  because,  if  working  with  well-known  and  tested  strains 
of  line-bred  stock,  one  or  two  tests  of  a  particular  combination  are 
as  good  as  a  dozen.  There  is  no  need  that  the  breeder  should 
waste  time  and  money  and  live  in  uncertainty  if  only  he  will  keep 
his  type  distinct,  his  blood  lines  pure,  and  will  test  every  animal 
that  is  to  have  a  permanent  place  in  the  herd.  If  he  will  not  do 
this  he  will  indeed  be  treading  a  maze  of  uncertainty,  and  will 
be  ready  to  say  at  the  end  of  a  long  life  and  as  the  fruit  of  his 
experience,  "Verily,  breeding  is  a  lottery,"  -  —  an  honestly  uttered 
but  gross  libel  on  one  of  the  greatest  professions  on  earth. 

Testing  sires.  A  well-established  herd  has  always  in  service  a 
mature  and  well-tested  sire  who  has  proved  his  breeding  power 
on  some  of  the  best-known  females  of  the  herd.1  Not  only  that, 
but  the  owner  of  such  a  herd  is  always  looking  for  his  successor. 

1  Among  the  many  answers  to  questions  touching  this  point  a  surprisingly 
large  proportion  of  breeders  confess  to  testing  bulls,  not  on  cows  of  known  breed- 
ing powers  but  on  heifers. 


ANIMAL  BREEDING  663 

If  an  old  and  proved  sire  can  be  had,  that  is  the  sire  to  buy, 
but  ordinarily  sires  of  this  kind  are  not  obtainable,  for,  if  they 
are  really  tested  sires,  they  are  usually  held  in  the  herd  that 
tested  them  until  their  period  of  usefulness  is  over.  If,  however, 
one  is  available,  it  is  a  treasure  that  should  not  go  begging, 
as  it  often  does.  If  the  young  breeder  would  make  it  a  rule  to 
buy  only  old,  tested  sires,  —  though  there  is  no  virtue  in  old 
sires  per  se,  —  he  would  do  better  breeding  than  many  another 
with  long  experience  behind  him  who  is  constantly  accumula- 
ting excellence  and  as  constantly  dissipating  it  by  the  use  of 
untested  sires. 

The  writer  has  conducted  an  extensive  correspondence  with 
breeders  of  cattle  on  this  point,  and  has  found  that  the  almost 
universal  practice  is  to  buy  a  young  bull,  probably  a  yearling, 
and  put  him  at  once  into  service  on  the  entire  herd.  This  is 
business  suicide,  for  it  constitutes  a  bar  to  any  very  high  degree 
of  success  and  is,  besides,  extremely  dangerous.  It  is  headed 
straight  for  mediocrity  —  within  the  breed  of  course,  but  it  is 
mediocrity  nevertheless. 

Testing  young  sires.  This  test,  to  be  most  valuable,  should 
be  made  on  some  of  the  better  females  of  the  herd,  whose 
breeding  powers  are  known.  It  would  be  folly  to  use  the  very 
choicest  individuals,  for  they  are  needed  for  more  certain  work 
with  the  tested  sire  at  the  head  ;  but  something  must  be  known 
about  the  females  on  which  even  the  preliminary  test  is  made, 
or  it  is  of  little  value. 

As  all  young  things  look  promising,  this  test  will  not  be 
worth  much  until  the  young  have  neared  maturity.  To  be  sure, 
some  individuals  will  be  so  unpromising  as  to  show  it  at  birth, 
or  soon  after,  but  very  many  mediocre  animals  will  not  make 
their  mediocrity  manifest  until  maturity  approaches.  They  then 
exhibit  their  inability  to  take  on  the  finer  finish  and  the  better 
touches  that  go  with  the  breed. 

On  this  point  experience  is  full.  One  of  the  finest  sucking  colts 
ever  known  to  the  writer  was  exceedingly  perfect  as  a  yearling, 
gave  good  promise  as  a  two-year-old,  commenced  to  fall  away  as 
a  three-year-old,  and  before  he  was  five  had  developed  into  a 
veritable  "  pelter  "  with  ewe  neck  and  sway  back. 


664  PRACTICAL  PROBLEMS 

If  the  young  that  are  to  show  the  breeding  powers  of  prospec- 
tive sires  must  reach  practical  maturity  much  time  will  be  con- 
sumed in  the  process.  In  cattle,  for  example,  the  young  must 
be  not  less  than  one,  and  preferably  they  should  be  at  least  two, 
years  old.  Practically  a  year  was  consumed  in  pregnancy,  and 
the  bull  was  a  year  old  at  the  time  of  service.  This  will  make  the 
prospective  sire  at  least  four  years  old  by  the  time  his  breeding 
powers  are  actually  known.  This  is  the  age  at  which  most  bulls 
are  sold  as  uugly  and  dangerous,"  a  practice  which  is  deplorable. 
All  bulls  are  ugly  or  dangerous,  or  both,  —  that  is  always  to  be 
assumed,  — but  at  four  years  of  age  they  are  just  ready  to  enter 
upon  the  period  of  real  usefulness,  and  the  records  will  show 
that  all  great  sires  have  done  their  work  not  as  yearlings  but 
later,  after  their  powers  were  known. 

Having  been  tested  and  proved  on  a  portion  of  the  herd,  a  sire 
is,  of  course,  placed  in  full  service,  and  it  is  but  business  sense 
to  make  the  most  of  him  as  long  as  he  is  able  to  continue  at  its 
head ;  it  is  even  more  business  sense  to  begin  at  once  to  look 
for  his  successor. 

A  herd  without  a  head.  Herds  pass  quickly,  and  a  herd  with- 
out a  head  is  doomed  to  speedy  extinction  unless  a  suitable  one 
can  be  found.  A  herd  in  such  a  condition  presents  a  hard 
problem  to  the  breeder  and  owner.  He  has  a  lot  of  accumulated 
excellence,  but  it  is  liable  to  die  before  he  can  use  it  unless  he 
puts  a  proper  sire  at  the  head  without  delay.  If  he  cannot  do 
that,  in  all  probability  dissipation  will  follow,  which  is  but 
another  form  of  extinction.  In  this  event  the  only  practical 
remedy  seems  to  be  dispersion,  and  this  is  the  real  reason  for 
more  than  one  of  the  dispersion  sales  that  come  along  each  year 
to  arouse  our  wonder. 

The  dispersion  sale  affords  an  exceptional  opportunity  to 
secure  real  excellence  in  breeders,  for  animals  are  there  offered 
that  ordinarily  no  purchaser  could  buy,  but  these  sales  are  not 
necessarily  for  the  best  interest  of  the  breed  ;  in  many  cases 
it  would  have  been  better  if  the  herd  could  have  been  kept 
together. 

Tested  individuals,  male  and  female,  are  the  backbone  of  the 
herd,  and  these  are  what  the  wise  breeder  will  preserve  through 


ANIMAL  BREEDING  665 

all  the  ups  and  downs  of  his  experience.  They  are  his  chief 
stock  in  trade,  and  he  will  cherish  them  as  any  other  business 
man  would  protect  a  vested  interest. 


SECTION  VI  —  WEATHERING  A  PERIOD  OF  DEPRESSION 
AND  PRESERVING  THE  HERD 

No  herd  can  live  without  ruining  its  owner  unless  sales  are 
made  regularly  and  at  good  prices.  It  is  a  stream  that  cannot 
be  stopped  without  damage. 

More  than  once  in  the  history  of  most  breeds  a  time  comes 
suddenly  when  for  some  reason,  or  for  no  assignable  cause, 
prices  drop  and  matters  collapse  generally.  This  calls  for  all 
the  ingenuity  of  the  breeder  and  all  his  fortitude  in  dealing 
with  a  difficult  situation. 

One  thing  is  certain,  —  the  herd  must  be  reduced.  It  is  simply 
business  folly  to  go  on  multiplying  animals  in  the  face  of  no 
market.  Such  a  course  leads  to  unmanageable  numbers,  and 
when  they  seem  to  have  lost  their  value  no  man  has  the  courage 
to  do  for  them  what  a  real  breeding  herd  requires.  Under  con- 
ditions such  as  this  the  herd  is  doomed  to  neglect.  It  is  only  a 
question  of  time  when  their  hungry  eyes  will  become  a  posi- 
tive source  of  displeasure,  if  not  of  disgust,  to  the  owner.  No 
one  ever  looked  upon  such  a  herd  without  a  feeling  of  sorrow, 
for  its  end  is  extinction,  even  though  the  storm  pass  and  the 
palmy  days  of  the  breed  return. 

Neither  is  the  other  extreme  to  be  advocated,  —  the  dumping 
of  everything  upon  the  open  market  for  what  it  will  bring.  The 
writer  has  seen  Shorthorns  that  cost  $300  to  $500  sold  to  the 
butcher  for  $40,  to  be  killed  and  eaten,  only  because  in  sudden 
panic  the  owners  had  assumed  that  the  Shorthorns  had  seen 
their  day. 

Now  a  really  excellent  breed  will  never  "  have  its  day."  If  it 
looks  that  way  it  means  only  that  the  day  will  come  again,  and 
not  so  very  far  in  the  future.  The  breed  has  served  us  before 
and  it  will  serve  us  again,  and  the  man  who  sells  the  cream  of 
his  herd  to  the  butcher  or  "  shoots  his  horses  to  feed  to  the 
hogs,"  — he  is  the  first  man  on  the  ground  to  restock  himself 


666  PRACTICAL  PROBLEMS 

at  long  prices  from  the  herds  of  those  who  were  wise  enough 
to  protect  themselves  and  make  everything  taut  while  the  storm 
might  last,  but  who  continued  in  business  against  the  day  when 
the  market  would  again  want  the  produce  of  their  herds. 

When  the  herd  is  reduced  at  such  a  time,  and  it  must  be 
reduced,  it  is  the  young  and  unproved  stuff  that  should  be 
sacrificed  first,  and  it  is  marvelous  how  much  can  be  sold  off 
without  disturbing  the  real  nucleus  or  producing  part  of  the  herd. 

If  the  herd  is  not  all  the  breeder  could  desire,  such  a  time  is 
the  most  favorable  opportunity  that  will  ever  appear  to  perfect 
the  herd  by  purchase.  This  is  the  time  to  gather  in  the  mothers 
and  the  grandmothers  of  the  breed  from  other  herds,  keep  them 
out  of  the  butcher's  hand,  and  set  them  at  work ;  and  about 
the  time  they  have  produced  another  generation,  their  former 
owners,  or  other  equally  anxious  purchasers,  will  be  ready  to  pay 
more  for  a  calf  than  the  tested  dam  and  sire  both  cost.  Every 
one  who  has  lived  long  among  breeders  has  seen  this  stampede 
out  of  the  business  followed  by  an  equally  insane  tumble  into  it. 
The  solid  breeder  will  hold  himself  well  together  at  such  a  time 
and  avail  himself  of  the  opportunity  both  to  improve  his  herd 
and  to  reap  an  assured  harvest  later  on. 

SECTION  VII  — RECORDS 

One  of  the  requirements  of  all  good  breeding  operations  is 
an  accurate  system  of  records,  covering  every  important  detail, 
leaving  nothing  to  memory.  Moreover,  the  record  should  be 
made  on  the  spot. 

Herd  records.  Simple  records  of  all  purchases,  sales,  births, 
and  deaths  are  matters  of  ordinary  business  accounts  and  inven- 
tory, but  in  addition  to  these  there  should  be  kept  what  may  be 
known  as  the  performance  record  of  the  herd.  This  consists  of 
three  distinctly  separate  features  : 

i.  An  accurate  description  in  writing  of  every  individual  ani- 
mal of  the  herd,  taken  not  only  at  maturity  but  at  birth  or  time 
of  purchase,  and  as  often  thereafter  as  changes  in  development 
occur.  Such  a  record  should  be  a  descriptive  history  of  the  in- 
dividual from  birth  to  death,  or  at  least  to  disposal,  accompanied 


ANIMAL  BREEDING  667 

by  photographs,  if  possible,  and  by  any  measurements,  weights, 
achievements,  or  facts  of  any  kind  that  may  later  assist  the  judg- 
ment in  basing  conclusions  as  to  selection.  The  record  of  the 
service  males  should  be  especially  full  and  complete. 

2.  A  full  description  of  every  individual  offspring  of  every  sire 
of  the  herd  as  compared  with  his  own  description  and  with  that 
of  the  dam,  —  such  a  series  of  descriptions  to  constitute  the 
breeding  record  of  the  sires. 

3.  A  breeding  record  should  be  opened  with  every  female  of 
the  herd,  showing  date  of  service  or  services,  xiate  of  birth  of  all 
offspring,  and  some  name  or  number  which  may  serve  as  an 
identification  mark  for  every  individual  produced,  whether  living 
or  dead. 

If  these  three  lines  of  data  are  kept,  the  breeder  will  have  not 
only  an  accurate  personal  description  of  every  animal  constitut- 
ing the  herd  and  every  one  produced  by  the  herd,  but  he  will 
also  have  a  complete  breeding  record  of  every  animal,  both  male 
and  female,  and  the  two  together  will  show  not  only  how  much 
each  animal  has  produced  but  also  what  was  its  quality.  When 
breeding  operations  have  been  carried  on  after  this  plan  for  a 
number  of  years,  such  records  will  constitute  a  mine  of  informa- 
tion which  no  memory  can  supply  with  sufficient  accuracy  to  be 
dependable.  Trusting  to  recollection  is  dangerous,  and  the  fleet- 
ing impressions  formed  of  certain  individuals  become  rapidly  dis- 
torted and  unreliable  as  time  passes,  —  how  rapidly  no  one  knows 
until  he  has  been  confronted  a  few  times  with  his  own  record 
made  first  hand  and  upon  the  spot.  These  records  are  essential 
to  the  best  breeding  and  absolutely  indispensable  to  the  man  who 
may  succeed  to  the  management  of  the  herd  later  on. 

Breeders  too  often  proceed  as  if  they  expected  to  live  forever, 
or  at  least  as  long  as  the  herd  exists,  whereas  we  must  look 
forward  to  the  time  when  an  established  herd  shall  outlast  the. 
lifetime  of  its  founder,  and  perhaps  two,  three,  or  more  genera- 
tions of  men  shall  be  involved  in  shaping  the  policies  of  its 
breeding,  —  all  of  which  is  possible  only  when  the  most  perfect 
records  are  kept. 

In  connection  with  private  herd  records  the  following  is 
appended  as  the  plan  in  actual  use  by  the  late  Honorable 


668 


PRACTICAL  PROBLEMS 


L.  H.  Kerrick,  of  Bloomington,  Illinois,  a  very  successful 
breeder  of  the  Aberdeen- Angus.  These  records  are  kept  on 
cardboard  5^  x  8|  inches,  and  containing  no  printing  whatever. 
They  are  kept  on  edge  in  alphabetical  order  in  a  special  box,  and 
it  is  but  a  moment's  work  to  note  the  present  condition  of  any 
female  in  the  herd  ;  moreover,  every  time  the  owner  consults  a 
card  he  is  afforded  at  a  glance  and  involuntarily  a  picture  of 
the  complete  breeding  record  of  the  cow  for  her  entire  lifetime. 
Two  records  are  presented,  one  of  Fair  Lady  of  Verulam  and 
the  other  of  her  first  offspring,  Fancy  Fair. 

f  Ermine  Bearer  .    1749 
9122  4  Fair  Lady  of  Chil- 

[    licothe  .    .     .     2760 
15215     Ellenreagh  of 

Kinnoul  Park  10203 
15094  C.  C.  Allen  .  .11266 
16988  Ebonist  .  .  .  5266 
19155  Ebonist  .  .  .  5266 
21243  Ebonist  .  .  .  5266 
23451  Craigo  of  Estill .  19518 
24961  Craigo  of  Estill .  19518 
27945  Craigo  of  Estill .  19518 
32444  Willis  E.  Gray  .  24751 
34196  Craftof  the  Wells  23450 
41949  Craftof  the  Wells  23450 
47813  Craft  of  the  Wells  23450 
57703  Painstaker  of 

Aberlour  .  .  34220 
75751  Painstaker  of 

Aberlour     .     .  34220 


March  ax, 1888 
June  20,  1890 

June  18,  1891 
April  1 8,  1892 
March  25,  1893 
March  12,  1894 
June  15,  1895 
May  2,  1896 
March  15,  1897 
January  27,  1898 
April  6,  1899 
March  30,  1900 
February  12,  1901 
January  17,  1902 


Fair  Lady  of  Verulam 

Fancy  Fair C. 

Wapella  Boy B. 

Ebon  Lizzie C. 

Bunty B. 

Irene  of  the  Wells  .     .     .  C. 

Lucy  M.  of  the  Wells.     .  C. 

Fairie  D C. 

Lygia  of  the  Wells      .     .  C. 

Florence  F.  of  the  Wells  C. 

Erie  of  the  Wells    .     .     .  C. 
Senator  Hoar  of  the  Wells  B. 

Statesman  of  the  Wells   .  B. 

Bunker  of  the  Wells    .     .  B. 


March  18,  1904        Florida  of  the  Wells    .     .    C. 


June  23.  1800 

Fancy  Fair  .... 

T  eoiS  " 

Ellenreagh    of 
Kinnoul  Park 

10203 

z  ••£)    *»yw 

August  20,  1892 
•  September  10,  1893 

Wapella  Lady  .... 
Fair  Fancy  . 

C. 
C. 

*0**3 

16991 
IQ24.I 

Fair  Lady  of 
L    Verulam    .     . 
H.  C.  Allen    .     . 
Ebonist      . 

9122 
11266 
5266 

July  2,  1894 
February  6,  1897 

Rose  F.  of  the  Wells  . 
Little  Ben  .  .  .  . 

C. 

B. 

y    T" 
36968 
27Q44 

Ebonist      .     .     . 
Craigo  of  Estill  . 

5266 

IQClS 

December  28,  1897 
January  21,  1899 
February  24,  1900 
January  15,  1901 

Operator  of  the  Wells  . 
Graymont  of  the  Wells  . 
Crouje  of  the  Wells  .  . 
Miss  West  of  the  Wells 

B. 
B. 
B. 
C. 

*/  yft 
27962 

32536 

41945 
47809 

Willis  E.  Gray   . 
Willis  E.  Gray    . 
Royal  Judge  . 
Painstaker  of 
Aberlour     .     . 

*yj 
24751 
24751 
20371 

34220 

ANIMAL  BREEDING  669 

December  1 6, 1901     Andee  of  the  Wells    .     .    6.50342     Painstaker  of 

Aberlour  .  .  34220 
November 20, 1902  Castro  of  the  Wells  .  .  6.57747  Painstaker  of 

Aberlour  .  .  34220 
December  2 1, 1903  Black  Heath  of  the  Wells  B.  72985  Painstaker  of 

Aberlour  .  .  34220 
November  27,  1904  Fan-Dan  of  the  Wells  B.  (Castrated)  Danwessels  of 

the  Wells  .    .  47821 

The  plan  of  the  record  is  simple.  It  shows  that  Fair  Lady  of 
Verulam,  born  March  21,  1888,  was  recorded  as  No.  9122; 
that  her  sire  was  Ermine  Bearer  1749,  and  her  dam  was  Fair 
Lady  of  Chillicothe  2760.  It  shows  that  her  first  calf  was 
dropped  June  20,  1890,  when  she  was  a  little  over  two  years  of 
age.  The  C.  shows  that  it  was  a  cow  calf.  It  was  named  Fancy 
Fair,  and  recorded  as  No.  15215.  Her  sire  was  Ellenreagh  of 
Kinnoul  Park  10203. 

Thus  the  first  name  in  the  first  line  is  that  of  the  cow  whose 
record  is  to  be  kept.  All  that  follow  in  her  line  are  her  offspring, 
and  all  the  names  of  the  second  column  are  their  sires,  except 
the  first  two.  Of  these,  one  (the  first)  is  her  own  sire,  the  other 
is  her  dam.1 

In  transmitting  these  data  Mr.  Kerrick  observed  : 

You  will  see  that  whenever  I  am  so  inclined,  I  can  commence  with  the 
letter  A  and  lift  up  these  cards  in  order  until  the  right  one  appears. 
Instantly,  when  I  lift  a  card,  the  life  performance  of  a  cow  is  shown.  It 
does  not  take  long  to  go  through  a  large  herd  and  see  just  what  each  cow 
is  doing.  If  I  find  a  number  of  cows  not  showing  a  calf  reasonably  near 
the  date  at  which  I  am  looking  through  the  cards,  we  can  make  a  note  in 
each  case. 

It  would  be  interesting  to  you  to  see  what  this  one  cow,  Fair  Lady  of 
Verulam,  has  done.  If  a  22-year-old  boy  would  luckily  buy  three  such 
cows,  he  would  have  a  fine  big  herd  at  32,  and  after  that  all  the  cattle  he 
would  want.  On  the  other  hand,  with  a  couple  of  shy-breeding  things,  and 
they  bringing  mostly  bulls,  he  might  not  have  any  more  at  32  than  when  he 
started  in  the  business.  A  big  part  of  our  herd  to-day  (numbering  over 
300)  are  descendants  of  Fair  Lady  of  Verulam. 

These  cards  might  well  be  extended  to  cover  other  details, 
especially  as  to  whether  the  offspring  is  retained  in  the  herd  or 
sold,  and,  if  sold,  to  whom  and  at  what  price. 

1  On  the  back  of  these  cards  is  an  outline  for  an  extended  pedigree. 


670  PRACTICAL  PROBLEMS 

This  latter  point  is  covered  in  the  system  in  use  by  A.  J.  Love- 
joy,  of  Roscoe,  Illinois,  a  well-known  breeder  of  Berkshires,  a 
sample  card  from  whose  herd  is  here  reproduced  : 

Index  No.  16.     Imported  Bessie  II  55101,  farrowed  April  10  to  Master- 
piece 77000.    Farrowed  5,  saved  5  :  boars  4,  sow  i 

Sold  boar  to  J.  W.  Martin,  Gotham,  Wisconsin  .     .     .    '.     .'.     '.     .$150.00 

"         "      "   L.  W.  Brown,  Berlin,  Illinois 75-oo 

"         "      "  J.  R.  Logan,  Seward,  Illinois      .........       50.00 

"         "      "  Hibbard  &  Brown,  Michigan 125.00 

"      sow    "  Nebraska  Insane  Hospital,  Lincoln,  Nebraska     .     .     .       50.00 
Total  for  litter  of  1905 $450.00 

In  connection  with  office  records  of  this  kind  the  "breeding 
book  "  kept  at  the  barn  should  record  the  date  of  every  service, 
the  date,  sex,  and  any  distinguishing  fact  concerning  the  birth 
of  every  individual,  living  or  dead,  and  any  other  fact  that  would 
prove  of  the  slightest  value  in  estimating  what  the  herd  is  doing 
or  has  done. 

If,  then,  in  addition,  there  were  kept  an  accurate  "  descriptive 
record"  of  every  individual  that  is  considered  worthy  to  enter 
the  herd,  or  to  be  sold  as  a  breeder,  and  besides  this  also  as  ac- 
curate a  record,  of  the  unworthy  products  of  the  herd,  the  breeder 
would  have  —  not  only  for  his  own  satisfaction  and  profit  when 
memory  fails  or  becomes  confused,  but  for  that  of  others  who 
may  handle  his  breeding  —  a  record  of  qualities  good  and  bad 
on  which  a  skillful  breeder  can  safely  base  his  selection.  With- 
out a  record  such  as  this  all  real  selection  is  limited  to  what  is 
done  with  the  eyes  on  animals-  still  living,  except  as  a  man  may 
be  guided  by  an  uncertain  memory.  How  uncertain  that  is  he 
will  realize  when  he  revisits  in  full  prime  of  life  the  hills  and 
valleys  of  his  boyhood. 

Pedigree  records.  That  which  is  needed  within  the  herd  is 
equally  important  within  the  breed.  The  facts  of  heredity  go 
to  show  that  all  good  breeding  requires  that  the  type  shall  be 
unchanged  for  at  least  six  generations,  if  we  hope  to  get  any- 
thing like  uniformity  of  offspring.  If  this  be  true,  we  need 
accurate  records  covering  all  important  details  and  all  valuable 
characters  for  at  least  the  six  generations  required  to  produce 
a  stable  type. . 


ANIMAL   BREEDING  671 

Now  our  pedigree  records  furnish  little  information  outside  of 
blood  lines,  and  they  are  totally  silent  as  to  what  the  individuals 
actually  were  in  their  own  personalities.  This  information  the 
breeder  needs  and  must  have  if  he  is  to  succeed.  Some  slight 
beginning  has  been  made  in  the  way  of  track  records  among 
racing  horses,  and  in  advanced  registry  among  dairy  cows. 
Then,  too,  breeders  aim  to  supply  in  their  private  catalogues 
some  detailed  information  about  particular  animals  ;  but  in  many 
cases  such  description  contains  so  large  an  element  of  adver- 
tising as  to  throw  doubt  upon  its  accuracy. 

As  the  case  stands  to-day,  there  is  no  way  in  which  an  impar- 
tial and  trustworthy  record  can  be  assured  even  of  our  most 
famous  and  valuable  animals.  This  being  the  case,  the  individual 
breeder  coming  into  the  business  must  devote  years  of  his  life 
to  the  accumulation  of  a  mass  of  data  more  or  less  reliable, 
gathered  irregularly  and  often  surreptitiously  from  the  under- 
current of  side  talk  in  which  old  and  prominent  breeders,  like 
other  mortals,  sometimes  indulge. 

Now  this  ought  not  to  be.  Such  information  belongs  to  the 
breed  and  to  future  breeders,  who  have  a  right  to  know  the  facts 
about  the  animals  whose  blood  lines  they  are  obliged  to  use  ;  and 
sometime,  in  some  way,  when  commercial  interests  are  no  longer 
supreme,  —  if  not  before,  —  an  accurate  and  impartial  descrip- 
tion of  every  great  animal  will  be  made  a  matter  of  permanent 
record  and  will  find  its  way  into  the  history  of  the  breed. 

It  is  to  the  interest  of  the  breed  that  this  should  be  so,  and  it 
is  also  to  the  interest  of  the  young  breeder,  that  he  may  proceed 
at  once  and  intelligently  with  his  breeding  operations  and  not 
spend  twenty  of  the  best  years  of  his  life  in  collecting  informa- 
tion by  indirect  and  often  devious  methods,  —  information  that 
is  by  good  rights  public  property,  and  as  such  is  the  rightful 
heritage  of  every  man  from  the  moment  he  becomes  a  breeder 
of  that  particular  breed. 

A  brilliant  future  awaits  the  breed  that  will  secure  and  put 
into  its  history  an  accurate  and  critical  description,  at  least  of 
every  famous  animal,  said  description  covering  all  distinguishing 
or  unusual  traits  both  desirable  and  undesirable,  and  not  confined 
to  extravagant  praise. 


6j 2  PRACTICAL  PROBLEMS 

If  this  is  ever  to  be  done,  some  feasible  plan  must  be  devised. 
Now  in  this  matter  two  things  are  self-evident :  first,  such  truth- 
ful and  critical  description  could  not  be  made,  or  at  least  made 
public,  during  the  lifetime  of  the  animal,  while  large  commercial 
interests  were  involved  ;  and  second,  more  than  one  man's  judg- 
ment should  be  consulted  in  making  the  actual  record. 

The  writer  ventures  to  suggest  that  while  the  animal  lives, 
and  is  in  his  prime,  and  while  his  character  and  achievements 
are  well  known,  a  full  statement  of  his  achievements  be  made 
and  two  critical  descriptions  be  prepared,  one  by  the  owner, 
the  other  by  a  committee  of  the  association,  —  all  to  find  a  per- 
manent place  in  the  published  records  of  the  breed. 

How  this  object  can  be  achieved  is  problematical,  but  until  it 
can  be  achieved,  the  best  results  in  animal  breeding  will  never 
be  possible.  One  thing  is  certain,  —  the  public  at  large  and  the 
association  of  breeders  in  particular  have  an  inherent,  if  not  a 
vested  right,  in  every  animal  that  comes  prominently  before  the 
public,  and  sometime,  in  some  way,  this  larger  right  of  public 
ownership  will  be  conceded  greatly  to  the  general  interests  of 
the  breed  and  to  the  convenience  of  future  breeders  ;  in  other 
words,  not  even  private  commercial  interests  will  always  inter- 
vene to  prevent  a  record  of  the  facts,  until,  by  the  death  of  all 
parties  possessing  actual  knowledge,  the  real  personality  of  a 
famous  animal  has  become  lost  beyond  the  power  of  restoration. 

The  blood  of  not  only  one  famous  animal  but  of  many  famous 
animals  runs  through  the  pedigrees  of  all  our  herds.  The  fame 
of  some  of  them  rested  on  real  excellence  and  well-earned  merit ; 
that  of  others  was  due  chiefly  to  skillful  management,  often  to 
shrewd  advertising.  Animals  of  both  classes  possessed  points 
of  high  excellence,  and  both  classes  also  possessed  defects.  The 
public  has  a  right  to  the  facts,  which  are  no  less  than  a  vested 
interest  to  every  man  who  owns  a  breeding  herd. 

SECTION  VIII  —  DISPOSAL  OF  SURPLUS  FEMALES 

The  herd  itself  must  make  the  first  draft  upon  its  female 
output  in  order  to  secure  material  to  reenforce  its  numbers. 
Some  females  will  be  needed  by  other  breeders  of  standing  to 


ANIMAL   BREEDING  673 

replenish  or  extend  their  herds.  What  shall  be  done  with  the 
rest  ?  The  answer  to  this  question  depends  somewhat  upon  the 
class  of  animals  and  the  circumstances  of  the  breeder,  but  on 
general  principles  the  destination  of  surplus  females  should  be 
the  open  market,  and  this,  destination  should  be  reached  as 
soon  as  possible  after  unfitness  to  take  a  place  in  the  permanent 
herd  is  well  established. 

The  one  thing  that  should  not  be  done  is  to  employ  this 
surplus  generally  as  material  for  the  establishment  of  new  herds. 
There  is  a  feeling  among  breeders  that  no  animal  eligible  to 
registry  should  be  sent  to  the  open  market,  especially  to  the 
shambles.  Nothing  could  be  more  erroneous.  To  use  surplus 
females  for  the  establishment  of  a  multitude  of  small,  weak 
herds  in  the  hands  of  men  who  have  no  experience  and  no 
genius  for  breeding,  is  at  first  to  arouse  vain  hopes  that  will  not 
be  realized  and  afterward  to  bring  down  curses,  not  only  on 
"blooded  stock"  and  breeders  in  general  but  on  this  special 
breed  in  particular. 

The  safest  and  the  best  destination  of  all  surplus  females  is 
the  open  market,  where  they  will  sell  for  what  they  are  worth 
and  be  entirely  safe  and  out  of  the  way,  with  a  small  but  safe 
balance  to  their  account  on  the  books  at  home,  after  having 
afforded  the  best  possible  practical  test  of  the  real  commercial 
value  of  the  type  that  is  being  bred  in  the  herd  which  they 
represent.  In  this  way  all  females  help  to  test  the  herd. 

SECTION  IX  — A  MARKET  FOR  SIRES 

It  is  quite  the  opposite  with  males.  The  great  business  of 
all  pure-bred  herds  is  the  production  of  sires,  and  the  country 
ought  to  be  industriously  campaigned  in  the  interest  of  "  placing  " 
sires  for  grading  purposes.  If  they  cannot  be  sold  let  them  be 
rented,  or  in  some  way  gotten  at  work.  Let  there  be  coopera- 
tion between  breeders,  even  between  breeds,  for  the  placing  of 
sires.  Let  salesmen  cover  the  country  as  do  agents  of  machinery, 
and  sell  sires  on  some  terms.  The  practice  of  grading  must 
be  brought  into  American  farming,  and  nobody  is  so  much 
interested  in  this  as  the  breeders  themselves.  The  common 


674  PRACTICAL  PROBLEMS 

stock  needs  the  sires  for  the  service,  and  the  breeders  need 
the  market. 

Breeders  are  selling  too  much  back  and  forth  among  them- 
selves. The  breeding  business  is  too  much  of  a  mutual  benefit 
association,  while  there  is  an  undeveloped  public  with  almost 
unlimited  buying  powers,  that  needs  to  be  educated  and  its 
buying  powers  developed.  Many  a  breeder  works  industriously 
to  sell  two  or  three  females  and  a  sire  to  a  novice,  partly  for  the 
money  that  is*  in  the  sale  and  partly  to  spread  the  gospel  of 
better  breeding,  as  he  thinks. 

It  does  not  work  that  way.  A  novice  has  been  started  in  a 
small  business.  The  chances  are  great  that  he  will  not  succeed. 
He  will  either  fail  and  curse  the  breed,  or  succeed  only  indif- 
ferently well  and  make  an  undesirable  competitor  who  is  willing 
to  sell  stock  of  the  "  same  breeding"  at  prices  much  below 
what  they  must  cost  when  produced  by  careful  breeding. 

If  the  same  man  had  bought  a  sire  he  would  have  been  satis- 
fied with  the  new  breed,  and  he  would  be  on  the  road  to  a  perma- 
nent habit  of  keeping  better  live  stock.  He  would  then  become  a 
customer  again  and  again.  From  any  point  of  view  the  breeders 
must  develop  the  market  for  sires  for  grading  purposes. 

SECTION  X  — COMMUNITY  BREEDING 

Many  advantages  will  follow  if  an  entire  community  will  go 
into  the  production  of  a  particular  class  of  animals,  as,  for 
example,  driving  horses.  There  are  a  thousand  little  details  in 
the  successful  management  of  any  business,  and  for  the  best 
success,  mind  must  react  upon  mind.  If  a  whole  community 
would  go  into  the  production  of  driving  horses  and  discuss  the 
driver,  his  breeding,  care,  development,  and  education,  as  com- 
munities now  discuss  corn  raising  in  the  corn  belt,  in  a  few 
years  every  man,  woman,  and  child  in  that  particular  locality 
would  "  know  all  about  horses."  They  would  soon  become 
skillful  drivers,  and,  as  is  now  the  case  in  the  famous  blue-grass 
region  of  Kentucky,  the  community  would  have  a  reputation 
that  would  attract  buyers,  and  a  horse  would  bring  more  money 
than  he  could  bring  if  he  were  the  only  one  in  the  neighborhood. 


ANIMAL  BREEDING  675 

Let  the  whole  community,  as  far  as  possible,  breed  the  same 
kind  of  horse  or  other  animal,  so  that  it  may  win  a  reputation 
for  a  distinctive  product,  and  it  will  not  only  do  better  breeding 
than  it  would  if  it  were  to  breed  many  types,  but  the  business 
will  be  vastly  more  profitable.  Practically  all  the  canaries  of 
the  world  are  bred  in  two  villages  in  Germany,  and  no  bird  with 
a  false  note  is  ever  allowed  to  live,  so  skilled  have  the  entire 
village  become  in  what  might  be  called  canary  excellence.  No 
individual  breeder  can  ever  equal  the  degree  of  success  which 
is  here  evolved,  where  practically  no  other  interest  engages 
the  attention  of  the  community. 

SECTION  XI  — THE  YOUNG  BREEDER 

There  is  no  reason  why  the  young  breeder  should  not  possess 
himself  thoroughly  and  quickly  with  the  principles  of  breeding. 
What  he  lacks  is  experience  with  animals  and  real  information 
about  breeds.  He  should  get  his  experience  either  by  grading 
or  by  association  with  a  good  herd,  but  he  must  needs  pick  up . 
his  information,  much  of  it  at  least,  from  intimate  association 
with  men  who  are  in  the  active  business  of  breeding. 

The  "  sucker  "  in  the  sales  ring.  Above  all,  the  young  breeder 
must  keep  his  head.  He  does  not  need  and  he  cannot  afford  to 
pay  large  prices  for  females.  If  he  sees  some  old  and  established 
breeder  bidding  high  on  a  young  female,  he  must  not  assume  that 
he  can  afford  to  bid  equally  high.  There  are  a  dozen  reasons 
why  the  older  breeder  may  want  that  particular  animal,  none  of 
which  would  apply  to  the  young  breeder.  For  example,  it  may 
be  the  only  one  of  that  particular  breeding  outside  the  herd  of 
the  older  breeder,  and  he  can  perhaps,  or  thinks  he  can,  afford 
to  pay  even  more  than  the  animal  is  worth  for  the  sake  of  con- 
trolling that  particular  combination ;  or  he  may  want  it  to  put 
into  the  show  ring,  or  to  mate  with  a  particular  sire.  None  of 
these  reasons  would  apply  to  the  young  breeder,  who,  if  he  buys 
it,  takes  it  for  its  merit. 

The  best  way  for  a  young  breeder  to  get  his  start  in  pure-bred 
animals  is  to  get  it  from  a  reputable  breeder  who  can  be  persuaded 
to  sell  some  really  excellent  and  tested,  or  partially  tested,  females. 


676  PRACTICAL  PROBLEMS 

It  is  doing  no  injustice  to  any  breed  to  remind  the  young 
breeder  that  the  bulk  of  young  things  come  to  very  little.  He 
will  be  safer  with  old  animals  —  even  those  of  considerable  age, 
providing  they  are  still  fertile. 

With  him  much  depends  upon  price.  He  has  no  call  to  pay 
extreme  prices.  He  cannot  sell  his  stuff  at  maximum  prices  till 
he  has  been  in  the  business  long  enough  to  acquire  something 
of  a  reputation,  and  one  of  his  best  early  reputations  is  as  a 
careful,  judicious  buyer. 

If  the  young  breeder  ever  loses  his  head  in  the  sales  ring,  let 
him  not  do  it  on  a  female,  that  can  at  best  produce  but  few,  or 
upon  extremely  young  things,  which  stand  about  as  many  chances 
of  coming  out  wrong  as  they  do  of  coming  out  right. 

ADDITIONAL  REFERENCES 

ANIMAL  BREEDING.  By  W.  M.  Hays.  Breeders'  Gazette,  XLV,  199, 
252,  305,  356,  461,  5*3,  565,  608. 

BREEDING  BEES  TO  INCREASE  LENGTH  OF  TONGUE.  By  J.  M.  Rankin. 
Michigan  Experiment  Station  Report,  1897,  p.  127  ;  also  in  Experiment 
Station  Record,  XI,  61,  1062. 

BREEDING  EXPERIMENTS  WITH  SHEEP.  Missouri  Experiment  Station, 
Bulletin  No.  53,  pp.  167-188;  also  in  Experiment  Station  Record, 
XIV,  383- 

BREEDING  POULTRY.    Experiment  Station  Record,  XIII,  176. 

BREEDING  POULTRY  FOR  EGG  PRODUCTION.  By  G.  M.  Gowell.  Maine 
Experiment  Station,  Bulletin  No.  79  ;  No.  93,  pp.  69-92  ;  also  in 
Experiment  Station  Record,  XV,  394. 

BREEDING  SHEEP  TO  CHANGE  BREEDING  SEASON.  By  T.  Shaw.  Min- 
nesota Experiment  Station,  Bulletin  No.  78,  pp.  71-87. 

CROSS-BREEDING  CHICKENS.  By  E.  P.  Miles.  Virginia  Experiment  Station, 
Bulletin  No.  96,  p.  6  ;  also  in  Experiment  Station  Report,  XI,  1074. 

CROSS-BREEDING  SHEEP.  By  F.  Winter.  Agricultural  Gazette,  London, 
1900,  p.  246. 

CROSS-BREEDING  SWINE.    Experiment  Station  Record,  XI,  1077. 

CROSSING  CATTLE.    Experiment  Station  Report,  VIII,  720. 

HYBRID,  GAMECOCK-GUINEA-FOWL.  By  T.  Vilaro.  Bulletin  of  the 
American  Museum  of  Natural  History,  1897,  p.  225  ;  also  in  Experi- 
ment Station  Record,  IX,  1031. 

PEDIGREE  STOCK  RECORDS.  (Report  of  Committee  on  Photographic 
Methods  of  Preserving.)  By  Francis  Galton.  Report  of  the  British 
Association  for  the  Advancement  of  Science,  1899,  pp.  424-429. 


CHAPTER  XXI 

DEVELOPMENT 

Thremmatology  is  interested  in  growth  as  well  as  in  reproduc- 
tion ;  in  the  proper  development  of  valuable  characters  as  well 
as  in  their  transmission  and  inheritance. 

What  an  individual  comes  to  be  at  maturity  is  a  kind  of  result- 
ant of  the  characters  born  into  him  and  the  opportunities  for 
their  development  afforded  by  the  conditions  of  life.  While  the 
surroundings  during  development  cannot  in  any  sense  compen- 
sate for  deficiency  in  inheritance,  the  opposite  is  also  true,  that 
the  richest  heritage  is  fruitless  of  results  if  conditions  of  life 
make  their  development  impossible. 

External  conditions  only  indirectly  causes  of  variation.  Con- 
ditions external  to  the  organism  thus  operate  only  indirectly  as 
causes  of  variation.  Their  good  results  depend  entirely  upon  the 
capacity  on  the  part  of  the  individual  or  the  breed  to  avail  itself 
of  their  advantages,  and  this  capacity  is  born  into  the  organism 
or  it  does  not  possess  it,  —  it  cannot  be  implanted  from  without. 
That  is  to  say,  no  amount  of  feeding  would  make  draft  horses 
out  of  those  that  are  racing  bred,  or  beef  cattle  out  of  those 
bred  for  the  dairy,  and  it  would  be  a  great  waste  of  feed  to  try 
it.  Certain  experiments  with  individual  animals,  it  is  true,  seem 
to  teach  that  Jerseys,  for  example,  are  successful  feeders.  Such 
experiments  will  deceive  no  one  who  realizes  the  full  extent  of 
variability  in  all  breeds,  and  that  individuals  can  be  found  to 
prove  almost  anything.  When  some  adventurous  investigator  will 
take  the  trouble  to  feed  off  three  hundred  Jerseys  against  three 
hundred  Shorthorns,  and  work  out  the  mean  and  the  standard 
deviation  for  both,  then  he  will  learn  that  a  breed  cannot  be 
selected  for  unknown  generations  for  milk  only,  and  still  retain 
or  attain  meat-producing  powers  equal  to  those  of  a  breed 
selected  almost  exclusively  for  that  purpose.  If  it  could,  there 
is  little  in  selection  and  less  in  breeding,  and  the  wonder  is  that 

677 


678  PRACTICAL  PROBLEMS 

anybody  ever  seriously  doubted  this  fact.  This  is  altogether 
outside  the  question  of  the  "dual  purpose"  animal,  for  no 
attempt  has  been  made  to  breed  the  Jersey  for  other  purposes 
than  milk  production.  Nor  is  it  a  reproach  to  Jerseys  that  they 
do  not  excel  in  something  for  which  they  have  never  been  bred. 
As  well  expect  them  to  take  records  upon  the  race  track,  or  to  do 
any  other  thing  for  which  they  have  not  been  fitted  by  selection. 

The  influence  of  the  environment  is  therefore  permissive 
rather  than  assertive.  It  affords  the  material  and  the  opportu- 
nity for  development  of  what  was  born  into  the  individual,  and 
what  was  not  born  into  it  cannot  develop,  no  matter  how  favor- 
able the  environment,  —  as  witness  the  very  different  develop- 
ment of  two  individuals  differently  born  but  living  under  the 
same  conditions  of  life.  If  an  individual  is  exceptional,  we  may 
say  of  him  with  confidence  that  he  was  both  well  born  and  well 
conditioned  during  development.  If,  on  the  other  hand,  he  is 
inferior,  we  are  uncertain  whether  to  attribute  it  to  non-inherit- 
ance of  valuable  characters,  or  to  their  failure  to  develop  owing 
to  unfortunate  conditions,  or  to  both. 

Well-bred  individuals  should  have  good  conditions.  It  is  mani- 
festly unwise  to  expend  time,  money,  and  thought  on  the  pro- 
duction of  individuals  highly  endowed  with  the  richest  possibilities 
of  the  race  and  then  fail  to  provide  the  necessary  conditions  for 
their  development.  Ordinary  business  sense,  therefore,  dictates 
that  the  breeder  should  secure  ideal  conditions  for  the  full  and 
proper  development  of  the  characters  whose  improvement  he 
aims  to  secure  through  fortunate  combinations  of  blood  lines. 
To  see  herds  of  the  best-bred  animals  suffering  for  feed  is  at 
once  pathetic  from  the  humanitarian  standpoint  and  unaccount- 
able from  a  business  standpoint. 

Having  spent  time  and  money  for  the  infusion  of  the  highest 
possibilities  into  the  herd,  certainly  business  foresight  demands 
that  their  full  realization  shall  be  prevented  by  no  ordinary  cir- 
cumstance ;  yet  what  share  of  the  best-bred  animals  and  what 
proportion  of  our  improved  seeds  are  given  full  opportunity  to 
show  what  is  really  in  them  ? 

The  breeder  is  interested  for  another  reason  in  securing  the 
full  development  of  all  that  is  born  into  individuals  and  family 


DEVELOPMENT 


679 


lines.  In  no  other  way  can  he  judge  of  their  real  excellence  and 
in  no  other  way  is  his  selection  safe.  The  practice  of  fitting  for 
the  show  ring  is  often  deplored,  and  not  without  good  reason, 
but  of  one  thing  we  may  be  well  assured,  —  we  can  never  be 
certain  of  the  capacities  of  an  individual  until  they  have  been 
put  to  the  test  by  development. 

One  of  the  hard  facts  of  animal  breeding  is  that  the  develop- 
ment of  young  things  is  very  often  left  to  men  who  are  not 
skilled  in  animal  production.  They  seem  to  assume  that  the 
well-bred  animal  in  some  way  can  get  along  under  less  favorable 
conditions  than  can  the  unimproved,  —  a  kind  of  offsetting  of 
breeding  against  feeding  and  care. 

Improvement  consists  in  producing  animals  and  plants  able  to 
make  good  returns  for  good  conditions,  not  merely  to  exist  under 
hard  conditions.  This  fact  ought  to  be  pasted  in  the  hat  of 
every  farmer.  The  purpose  of  breeders  is  not  to  produce  strains 
that  can  live  on  next  to  nothing,  and  that  are  able  to  endure 
hard  conditions  and  not  die  outright ;  it  is  to  produce  strains  of 
animals  and  plants  that  are  able  to  make  good  returns  for  the 
fuller  feed  and  better  care  which  the  civilized  and  educated 
farmer  can  give  as  compared  with  nature,  which  is  capricious, 
or  with  the  unskillful  semi-savage,  who  is  improvident. 

One  of  the  most  serious  faults  of  unimproved  strains  is  that 
they  do  not  respond  to  better  food  or  to  more  of  it.  They  have 
been  selected  for  generations  for  their  powers  of  resistance  to 
hard  conditions,  and  that  is  where  their  strength  lies.  Now  that 
we  can  provide  better  food,  we  need  animals  of  higher  efficiency  ; 
indeed,  that  is  our  argument  for  better  animals.  Then,  again, 
having  animals  of  higher  efficiency,  we  need  better  feed  and 
more  of  it,  and  that  is  our  argument  for  better-bred  corn  and 
other  crops.  So  the  two  —  animal  breeding  and  better  feeding 
—  react  the  one  upon  the  other,  and  both  go  with  better  farming 
and  with  the  greater  needs  of  an  advancing  civilization. 

The  well-bred  animal  is  a  high-class  machine.  This  fact  can- 
not be  too  well  understood  by  every  man  who  comes  into  relations 
with  the  well-bred  animal,  and  it  is  true,  whether  we  consider 
animals  as  machines  for  the  producing  of  milk  or  meat,  of  labor, 
or  of  body  covering ;  whether  we  consider  that  they  are  to 


680  PRACTICAL  PROBLEMS 

minister  to  our  necessities  or  to  cater  to  our  enjoyment  by 
personal  service,  as  with  the  saddler  and  the  driving  horse. 

Excellence  is  not  to  be  measured  by  the  power  to  withstand 
deprivation,  but  rather  by  efficiency  to  do  work  under  full  feed 
and  under  good  conditions ;  and  to  this  end  it  is  but  good  busi- 
ness sense  to  secure  for  each  individual  the  full  development  of 
all  the  useful  qualities  with  which  he  is  naturally  endowed. 

Development  is  a  study  by  itself.  Here  is  an  entire  field 
almost  unexplored.  We  know,  in  a  general  way,  that  the 
"energy  of  embryonic  development"  is  never  attained  later  in 
life,  and  that  if  we  would  secure  full  development  in  growth  we 
must  "keep  the  young  thing  growing."  In  some  way  or  other 
this  business  of  body  development,  if  once  checked,  is  never 
again  fully  resumed.  It  is  true  that  a  few  experts  have  learned 
fairly  well  how  to  develop  speed  in  horses,  and  others  how  to 
train  saddlers  and  drivers  ;  but  whether  we  consider  the  growth 
of  the  body,  the  development  of  its  functions,  or  the  education  of 
the  mental  faculties,  we  do  not  yet  possess  even  the  rudiments  of 
the  knowledge  of  the  most  successful  development.  With  us  only 
an  occasional  individual  enjoys  optimum  conditions  throughout 
his  life,  and  only  a  few  exhibit  in  their  own  personality  the  really 
wonderful  capacity  of  the  breed  to  which  they  belong.  If  one 
were  to  say  that  the  science  and  practice  of  breeding  is  far  better 
known  than  that  of  development  afterward,  he  would  be  well 
within  the  truth,  and  in  the  opinion  of  the  writer  here  will  lie 
some  of  our  greatest  improvements  of  the  near  future.  The 
excessive  fitting  of  an  occasional  individual  for  the  show  ring, 
regardless  of  consequences  afterward,  is  not  what  is  here  meant, 
but  rather  the  orderly  and  full  development,  in  substantially  all 
individuals,  of  those  qualities  which  we  deem  valuable,  so  that 
we  may  fully  realize  in  our  animals  the  qualities  we  select  and 
breed  for  in  our  yards. 


APPENDIX 

STATISTICAL  METHODS 

BY  H.  L.  RIETZ,  PH.D. 

Assistant  Professor  of  Mathematics,  University  of  Illinois 

SECTION   I  — INTRODUCTION 

An  elementary  account  of  the  mathematical  theory  of  statistics  in  a 
treatise  on  Thremmatology  needs  no  justification  after  the  foregoing  text. 
The  doctrines  of  evolution  and  heredity  rest  on  a  statistical  basis,1  because 
we  are,  in  general,  concerned  with  groups  of  individuals,  and  with  occur- 
rences of  such  a  nature  that,  although  we  cannot  make  definite  quantitative 
statements  about  any  one  of  them  taken  singly,  we  can  make  statements 
in  regard  to  a  large  number  of  them  taken  together  with  a  degree  of  cer- 
tainty which  increases  as  the  number  increases.  For  example,  a  thousand 
ears  of  corn  may  vary  in  length  from  three  inches  to  eleven  inches  and 
have  an  average  (average  to  be  defined  in  Section  II)  length  of  8.5  inches. 
We  cannot  state  with  any  degree  of  certainty  the  length  of  an  ear  selected 
at  random  out  of  this  group  of  a  thousand  ears  ;  but  if  we  select  at  random 
five  hundred  ears  out  of  the  thousand  we  can  assert  with  considerable  confi- 
dence that  the  average  length  of  the  five  hundred  ears  will  differ  but  little 
from  8.5  inches. 

The  important  questions  in  every  case  are  these :  In  what  way  can  we 
best  describe  a  population  whose  variates  we  have  measured  ?  How  can 
we  give  the  meaning  and  information  contained  in  this  mass  of  figures  in 
a  few  words  or  symbols  ? 

A  glance  at  the  figures  may  give  a  personal  impression,  but  this  is  not 
reliable,  as  is  proved  by  the  fact  that  two  persons  may  each  get  a  very 
different  personal  impression,  even  when  examining  the  same  set  of  figures. 
We  must  here  resort  to  more  exact  methods,  and  it  is  the  object  of  this 
appendix  to  present  in  a  brief  and  elementary  manner  the  mathematical 
methods  of  dealing  with  such  masses  of  figures. 

SECTION   II— AVERAGES 

• 

Meaning  and  function  of  an  average.  The  fundamental  questions  which 
arise  in  the  discussion  of  averages  are:  (i)  What  is  meant  by  "the  aver- 
age of  a  system  of  variates  "  ?  (2)  Why  do  we  make  use  of  averages  at 

1  See  Karl  Pearson,  Grammar  of  Science. 
68 1 


682  APPENDIX 

all  ?  (3)  What  are  the  objects  of  having  different  kinds  of  averages  ? 
Such  questions  as  these  are  apt  to  be  overlooked  by  those  who  have  formed 
the  habit  of  averaging  all  kinds  of  results  without  careful  thought. 

In  popular  language,  we  speak  of  the  average  daily  temperature,  the 
average  length  of  ears  of  corn,  the  average  student,  the  average  citizen ; 
and  we  should  know  the  exact  meaning  to  be  conveyed  by  these  and  simi- 
lar expressions  before  using  them  in  scientific  discourse. 

The  taking  of  an  average  presupposes  a  population  whose  variates  have 
a  certain  measurable  character  about  which  we  are  concerned,  and  that 
the  measurement  of  this  character  differs  in  different  individuals.  We 
attempt  to  describe  this  population  by  putting  aside  the  measurements  of 
individuals  and  constructing  a  single  intermediate  number  which  shall  be 
descriptive  of  the  total  population,  in  so  far  as  one  number  can  describe 
a  population. 

The  single  intermediate  number  which  answers  this  purpose  is,  in  the 
general  sense,  some  kind  of  an  average.  We  thus  use  averages  for  descrip- 
tive purposes  in  the  interest  of  brevity ;  but,  taken  alone,  an  average  can- 
not completely  describe  a  population  any  more  than  the  motion  of  the 
center  of  gravity  of  a  system  of  material  particles  can  completely  describe 
the  motion  of  the  separate  particles. 

In  stating  what  an  average  is  we  have  also  stated  its  function ;  but,  as 
just  indicated,  it  must  not  be  assumed  that  an  average  gives  all  the  infor- 
mation which  is  to  be  secured  from  the  measurement  of  a  population.  It 
can  only  take  the  place  of  the  mass  of  figures  for  certain  special  purposes. 
In  fact,  there  has  been  a  tendency,  by  somewhat  careless  workers  with 
statistical  data,  to  attach  too  much  importance  to  averages  and  not  enough 
to  deviations  from  the  average,  —  a  point  that  will  be  dealt  with  in  a  later 
section. 

There  are  five  different  kinds  of  averages  in  common  use  for  different 
purposes.  These  are  (i)  the  arithmetic  mean,  (2)  the  weighted  arithmetic 
mean,  (3)  the  geometric  mean,  (4)  the  mode,  (5)  the  median. 

While  some  of  these  averages  have  been  defined,  and  used  freely  in  the 
text,  it  seems  well  to  restate  these  definitions  together  with  the  others,  the 
better  to  discuss  their  respective  advantages  and  disadvantages,  and  some 
of  the  purposes  to  which  each  is  adapted. 

The  arithmetic  mean.  The  arithmetic  mean  of  a  population  of  n  variates 
may  be  defined  as  follows : 

sum  of  measurement  of  n  variates 

arithmetic  mean  = 

n 

That  is,  to  find  the  arithmetic  mean  of  n  variates,  we  divide  the  sum  of  the 
measurements  of  these  variates  by  the  number  of  variates. 

Thus,  in  the  case  of  a  thousand  ears  of  corn,  the  arithmetic  mean  of  the 
lengths  of  the  ears  is  the  sum  of  the  lengths  of  1000  ears  divided  by  1000. 
The  use  of  this  kind  of  an  average  has  always  been  taken  by  observers  as  the 
best  method  of  combining  direct  measurements  of  the  same  quantity.  This  is 


APPENDIX 


683 


the  average  most  commonly  employed,  and  one  of  the  strongest  arguments 
advanced  to  justify  this  method  is  its  universal  acceptance.  It  is  worth 
while,  however,  to  call  attention  to  one  of  the  abuses  of  the  arithmetic 
mean.  For  instance,  if  a  very  few  (say  four)  measurements  have  been 
made  of  a  certain  character,  the  arithmetic  mean  has  often  been  taken  as 
a  good  index  of  their  meaning ;  but  if  these  few  measurements  differ 
widely,  to  report  their  arithmetic  mean  is  to  furnish  a  very  misleading  and 
untrustworthy  piece  of  information.  This  has  often  been  done  by  those 
who  have  given  no  thought  to  statistical  methods. 

There  is  a  sort  of  commercial  point  involved  in  the  arithmetic  mean 
which  should  not  be  overlooked.  For  instance,  if  a  real  estate  dealer  sells 
a  hundred  lots  at  various  prices,  of  which  the  arithmetical  average  is  $800, 
this  assures  us  that  if  the  seller  had  sold  each  of  the  lots  for  $800,  instead 
of  selling  at  different  prices,  he  would  have  realized  precisely  the  same 
from  the  sale  of  the  whole  number  of  lots  as  he  has  realized  from  selling 
at  varying  rates,  even  though  we  have  no  information  as  to  what  any  indi- 
vidual has  paid  for  a  lot. 

Weighted  arithmetic  mean.  A  slight  modification  of  the  above  method 
is  often  used.  To  illustrate,  the  thousand  measurements  of  lengths  of  ears 
of  corn  may  be  arranged,  let  us  say,  in  half-inch  groups  as  follows : 


Inches  .... 

3-° 

3-5 

4.0 

4-5 

5-° 

5-5 

6.0 

6-5 

7.0 

7-5 

8.0 

8-5 

g.o 

9-5 

10.0 

10.5 

II.O 

,..s 

Frequencies  .  . 

5 

6 

'3 

17 

18 

55 

61 

73 

80 

„ 

113 

.» 

142 

100 

53 

26 

5 

• 

where,  for  instance,  the  6-inch  group  includes  all  ears  whose  lengths  are 
between  5.75  and  6.25.  In  general,  if  vv  vz, . . .,  vr  represent  the  class  marks, 
and/^,/2,  "'ifr  represent  the  corresponding  frequencies,  then 

weighted  arithmetic  mean  =/iyi +/«"«  +  ' ' ' +/^  . 

/I   +/2  +  ~'+fr 

Stated  in  words,  this  mean  is  obtained  by  multiplying  each  mark  of  a 
class  by  the  corresponding  frequency,  and  dividing  the  sum  of  the  products 
by  the  total  population. 

This  kind  of  average  is  used  a  great  deal  in  our  work  and  is  approxi- 
mately equal  to  the  ordinary  arithmetical  average  if  the  groups  are  fairly 
narrow.  Its  advantage  over  the  ordinary  arithmetic  mean  lies  in  the  fact 
that  it  is  more  easily  computed.  In  reporting  the  mean  daily  temperature, 
the  average  length  of  ears  of  corn,  the  average  height  of  a  certain  class  of 
men,  one  of  the  above  kinds  of  averages  is  meant.  We  use  these  averages 
so  much  in  this  work  that  we  speak  of  them  as  "  the  mean,"  for  brevity, 
so  that  when  the  term  "  mean  "  is  used  without  a  limiting  adjective,  it  is  to 
be  understood  that  an  arithmetic  mean  is  meant. 

The  geometric  mean.  The  geometric  mean  of  n  numbers  is  found  by  mul- 
tiplying the  numbers  together  and  extracting  the  nth  root  of  the  product. 


684  APPENDIX 

Let  us  assume  that  during  a  decade  the  attendance  at  a  university  in- 
creased 100  per  cent,  and  let  us  propose  the  problem  of  rinding  the  average 
annual  rate  of  increase.  Will  it  do  to  resort  to  the  arithmetic  mean  in 
this  case  and  say  that  the  average  rate  of  increase  is  10  per  cent  ?  No  ;  an 
increase  of  10  per  cent  annually  would  give  an  attendance  (i.io)10  =  2.59 
times  the  attendance  at  the  beginning  of  the  decade.  What  we  really  want 
is  ^2~=  1.07  +  ;  that  is,  an  increase  of  a  little  more  than  7  per  cent  each 
year  will  double  the  population  in  a  decade. 

The  geometrical  average  is  but  little  used  in  our  work,  but  it  is  brought 
forward  here  to  remind  us  that  an  average  can,  in  general,  be  depended 
upon  only  to  serve  a  definite  purpose  ;  and,  when  the  purpose  is  known,  we 
are  sometimes  confined  to  one  kind  of  average,  or  at  least  able  to  see  the 
advantage  of  one  kind  of  average  over  another.  Suppose  that  we  know  the 
protein  content  of  corn  to  have  been  increased  50  per  cent  in  ten  years' 
breeding.  Can  we  say  that  the  average  annual  rate  of  increase  was  5  per 
cent  ?  Clearly  we  cannot.  What  we  should  do  is  to  take 

^1.50  —  i  .00  =  0.041 

and  say  that  the  average  annual  rate  of  increase  is  approximately  4  per  cent. 

The  mode.  When  we  speak  of  the  average  college  student  or  the  aver- 
age citizen  we  certainly  do  not  have  reference  to  the  arithmetic  or  geo- 
metric average  of  anything.  When  we  say  a  man  is  an  average  citizen 
we  mean  that  he  represents  a  type  which  is  met  oftener  than  any  other. 

If  a  community  has  ten  millionaires,  but  all  the  other  citizens  are  in  pov- 
erty, an  arithmetical  average  might  give  the  impression  that  the  people  of 
the  community  are  in  good  financial  condition,  while  really  the  "  average 
citizen "  is  in  poverty.  The  averages  thus  far  discussed  are  in  no  way 
suited  to  describe  this  population,  but  the  average  called  the  "  mode  "  is 
useful  for  this  purpose. 

If  a  population  be  arranged  in  seriate  order  with  respect  to  some  char- 
acter, a  mode  is  a  value  to  which  there  corresponds  a  greater  frequency 
than  to  values  just  preceding  and  immediately  following  it  in  the  arrange- 
ment. A  population  may  have  more  than  one  mode,  but  the  populations 
with  which  we  shall  deal  have,  in  general,  only  one. 

This  kind  of  average  seems  to  be  about  the  same  as  that  of  the  news- 
papers when  they  speak  of  the  average  citizen.  In  a  democracy  we  often 
hear  the  cry  of  "  the  greatest  good  for  the  greatest  number,"  and  insist  that 
legislation  shall  benefit  the  average  man,  —  the  man  at  the  mode. 

Reverting  again  to  the  thousand  ears  of  corn  arranged  in  half-inch  groups, 
it  should  be  noted  that  the  frequency  increases  up  to  the  class  of  mark 
9  inches  and  then  decreases.  We  might  conclude  that  9  inches  is  exactly 
the  mode  for  this  population.  It  must  be  remembered  that  all  measure- 
ments from  8.75  to  9.25  inches  were  placed  in  the  9-inch  group,  and  that 
a  different  grouping  might  change  the  frequencies  somewhat.  Hence  9  is 
said  to  be  the  empirical  mode,  and  the  theoretical  mode  is  defined  as  a 


APPENDIX  685 

point  of  greatest  frequency  of  the  theoretical  distribution,  of  which  the 
given  distribution  is  a  sample.  As  a  disadvantage,  it  should  be  mentioned 
that  it  is  somewhat  difficult  to  determine  the  theoretical  mode  accurately. 
It  may  also  be  pointed  out  that  for  a  very  irregular  group  of  figures  the 
mode  is  practically  useless.  Its  great  service  is  to  characterize  a  type,  and 
with  a  very  irregular  group  of  figures  the  existence  of  a  type  is  not  mani- 
fest ;  indeed,  a  type  may  not  exist. 

The  median.  If  all  the  variates  are  arranged  in  serial  order,  the  value 
corresponding  to  the  middle  variate  is  called  the  median  of  the  population. 
Thus,  if  we  should  speak  of  the  wages  of  a  thousand  and  one  laborers,  we 
should  mean  by  the  median  the  wages  of  the  middlemost  of  these  men 
when  they  are  arranged  in  serial  order  with  respect  to  wages ;  that  is,  if 
five  hundred  received  less  than  $1.72,  and  five  hundred  received  more  than 
$1.72,  we  should  say  that  $1.72  is  the  median  wage.  The  median  has  the 
great  advantage  that  it  can  be  easily  determined.  Very  large  and  very 
small  values  do  not  affect  it.  It  is  only  a  question  of  being  above  or  below 
the  middle  in  an  arrangement.  Its  great  disadvantages  are  that  it  may  be 
totally  removed  from  the  type  and  that  it  gives  no  special  importance  to 
extreme  values. 

Averages  of  whatever  kind  are  designed  to  exhibit  the  main  features  of 
a  population  by  means  of  a  few  well-chosen  numbers.  We  have  seen  that 
the  particular  average  selected  depends  upon  the  purpose  we  have  in  view. 
Now,  if  this  purpose  is  merely  one  of  comparison  between  two  similar 
groups,  then  almost  any  kind  of  an  average  will  do.  The  ordinary  and  the 
weighted  means  have  been  used  for  the  mo^t  part  in  this  work,  but  con- 
ditions may  easily  arise  where  some  other  average  is  more  suitable.  Bowley 
has  well  stated  the  following  as  the  characteristics  of  a  good  and  suitable 
average :  "  If  there  is  a  type,  it  shows  it ;  it  gives  due  influence  to  extreme 
cases  ;  it  is  not  easily  affected  by  errors,  or  much  displaced  by  slight 
alterations  in  the  system  of  calculations ;  and  it  is  easily  calculated." 

It  is  often  useful  to  give  more  than  one  average  in  order  to  describe  a 
population  ;  for  the  relative  positions  of  the  mean,  the  mode,  and  the  median 
give  a  good  deal  more  information  about  the  distribution  of  a  population 
than  any  single  average  can  give.  For  a  great  many  distributions  Pearson 
has  found  an  approximate  relation  to  exist  between  the  mean,  the  mode, 
and  the  median.  This  relation  is 

theoretical  mode  =  mean  —  3  (mean  —  median). 

It  is,  of  course,  possible  to  form  fictitious  frequency  distributions  for 
which  this  relation  does  not  hold,  but  it  is  important  as  indicating  what 
nature,  in  general,  provides. 

The  use  of  averages  for  representing  what  is  often  spoken  of  as 
the  "true  value"  can  be  better  discussed  in  the  section  devoted  to  the 
probable  error. 


686 


APPENDIX 


SECTION   III  — GRAPHIC  REPRESENTATION   OF 
STATISTICS 

A  mere  tabulation  of  any  considerable  number  of  figures  does  not  make 
it  possible,  in  general,  for  the  mind  to  grasp  the  main  facts  which  the 
figures  represent ;  in  fact,  such  a  tabulation  of,  say  a  thousand  figures,  may 
make  no  impression  on  the  mind  which  is  at  all  worth  mentioning.  By  the 
graphic  method,  however,  the  chief  characteristics  of  a  mass  of  figures  are 
presented  to  the  eye  by  means  of  a  picture  or  curve.  The  graph  gives, 
at  a  glance,  important  facts  which  may  be  overlooked,  or  which  can  be 
obtained  from  the  figures  only  by  considerable  labor. 

The  use  of  graphic  methods  in  statistics  is  very  extensive,  and  has  proved 
to  be  of  great  service.  In  fact,  everyone  who  has  to  deal  with  complicated 
groups  of  figures  comes  to  appreciate  the  graphic  method,  as  it  enables  one 
to  perceive  relations  through  the  eye. 

It  is  the  object  of  this  section  to  show  how  graphs  are  formed  from  given 
data. 

Frequency  curves.  Let  us  consider  the  graph  of  the  following  frequency 
distribution,  in  which  the  first  line  of  the  table  gives  the  marks  of  the 
classes,  and  the  second  gives  the  number  of  variates  in  the  classes : 


Values    

4.0 

4-5 

5-o 

5-5 

6.0 

6.5 

7.0 

7-5 

8.0 

8  c 

9.0 

9-5 

IO.O 

Frequencies  .... 

< 

i 

8 

33 

70 

no 

176 

172 

124 

61 

32 

10 

2 

What  we  propose  to  do  here  is  to  present  a  significant  picture  of  this 
population. 

Draw  two.  lines,  OX  and  OY,  at  right  angles  to  each  other  (Fig.  i). 
These  reference  lines  are  called  coordinate  axes.  The  line  OX  is  called 
the  ^--axis,  and  the  line  (9Fthe  j-axis.  The  point  (9,  from  which  we  meas- 
ure, is  called  the  origin,  or  zero  point.  Beginning  at  this  point  mark  off 
on  the  ;r-axis  equal  intervals  upon  a  scale  convenient  to  the  problem  at 
hand.  From  the  same  zero  point  lay  off  equal  intervals  also  on  the  j-axis. 
These  need  not  be  on  the  same  scale  as  those  on  the  .r-axis,  but  should 
be  suited  to  best  bring  out  the  facts  to  be  shown  by  the  graph.  Not  all 
graphs  are  drawn  upon  the  same  scale  therefore,  nor  are  the  two  axes  of 
the  same  graph  alike  as  to  spacing  or  scale. 

In  the  particular  case  in  hand,  let  each  interval  along  OX  represent  a 
half  inch.  The  question  as  to  what  each  interval  shall  represent  is  a  matter 
of  the  scale  used  ;  and  the  scale  must  be  chosen  to  suit  the  particular  data 
in  hand.  Next,  along  OX  lay  off  the  class  marks.  Corresponding  to  each 
class  mark  there  is  a  frequency.  From  the  various  points  on  the  ^r-axis 

1  This  distribution  is  taken  as  a  representative  of  any  frequency  distribution.  It  is  not, 
however,  made  up  artificially,  but  actually  represents  the  distribution  of  eight  hundred  ears 
of  corn  with  respect  to  length. 


APPENDIX 


687 


which  represent  class  marks  lay  off  lines  parallel  to  the  j-axis  and  of 
lengths  corresponding  to  the  various  frequencies,  according  to  the  scale  on 
the  j-axis.  When  this  is  done  there  will  be  a  series  of  parallel  lines  at 
equal  distances  apart,  all  perpendicular  to  the  .r-axis  and  parallel  to  the 
j-axis,  but  of  lengths  corresponding  to  the  various  frequencies  and  therefore 
unequal.  Joining  the  tops  of  the  lines  so  constructed  by  straight  lines 
gives  the  frequency  polygon  shown  in  Fig.  I.  The  tops  of  the  lines  thus 
joined  give  an  orderly  arrangement  of  points,  through  which  it  may  be 
possible  to  draw  a  smooth  curve.  If  it  is  impossible  to  draw  a  smooth  curve 
through  all  of  them,  draw  a  smooth  curve  as  near  as  possible  to  all  of  them. 
The  curve  so  drawn  is  called  a  frequency  curve  (not  shown  in  figure). 

r 


O'JE 


ll'U 


"l-P 


71 


0  4     4.5     5     5.5    -6     6.5     7     7.5     8     8.5     9     9.5   10 

FIG.  i 

Any  point  P  in  the  plane  represents  two  numbers :  the  one  number  is 
represented  by  the  distance  of  the  point  from  the_y-axis,  and  the  other  by 
its  distance  from  the  .r-axis.  The  number  which  gives  the  distance  of  P  from 
the  j-axis  is  called  the  abscissa  of  P,  and  the  number  which  gives  its  distance 
from  the  ^r-axis  is  called  its  ordinate.  .  The  two  numbers  together  are  often 
spoken  of  as  the  coordinates  of  the  point  P. 

Significance  of  area  under  curve.  Construct  rectangles  such  as  ABCD 
and  BC ' EF  on  the  ordinates  at  class  marks  as  mid-lines,  making  the  sides 
AD,  BC,  etc.,  bisect  the  class  intervals  along  the  .r-axis.  Suppose,  now, 
that  we  define  unit  area  as  a  rectangle  bounded  by  AB,  AD,  BC,  and  a 
line  parallel  to  AB  and  just  far  enough  from  it  so  that  the  distance 
between  AB  and  this  line  represents  unit  frequency.  Then  the  area  of 
ABCD  is  1 10,  and  the  area  of  all  such  rectangles  taken  together  is  equal 
numerically  to  the  total  population.  In  drawing  the  smooth  curve  men- 
tioned above,  we  should  aim  to  make  the  area  between  the  curve  the 


688 


APPENDIX 


.r-axis,  and  the  two  end  ordinates  (in  this  case  ordinates  at  4  and  10)  equal 
to  the  sum  of  the  areas  of  these  rectangles.  The  area  under  the  curve 
then  represents  the  total  population.  This  is  an  important  point,  because 
it  presents  to  the  eye  how  much  of  the  population  is  included  between  any 
two  measurements.  For  instance,  at  a  glance  you  could  estimate  approxi- 
mately the  portion  of  the  population  discussed  in  Fig.  i,  whose  measure- 
ments are  between  5  and  8.  The  use  of  the  area  under  the  frequency  curve 
will  be  found  helpful  in  our  discussion  of  "probable  error." 

Choice  of  scale.  In  drawing  a  graph  the  question  always  arises  as  to 
what  scale  shall  be  used  in  plotting,  but  unfortunately  no  definite  rule  can 
be  laid  down.  It  may,  however,  prove  useful  to  call  attention  to  a  few 
points.  First,  we  should  choose  such  a  scale  that  we  can  plot  all  the  points 
on  one  page  of  the  paper  used;  for  it  is  a  great  advantage  to  have  the 
whole  graph  on  one  paper,  thus  making  it  visible  to  the  eye  in  its  entirety. 
Second,  if  the  point  involved  in  the  investigation  is  a  question  of  rate  of 
increase  or  decrease,  we  should  select  such  a  scale  as  to  make  the  curve 
reasonably  steep.  Frequency  curves  are  used  a  great  deal  in  the  study  of  the 
social  sciences,  as  well  as  in  natural  science.  For  instance,  the  sociologist 
presents  the  population  of  a  city  or  country  for  successive  years  by  using 
years  as  the  marks  of  classes,  —  laying  these  off  along  the  .r-axis,  —  and 
the  population  for  these  years  as  ordinates. 

Negative  values  easily  represented  graphically.  We  often  desire  to  plot 
negative  values  as  well  as  positive  values,  and  this  is  easily  accomplished 
by  a  slight  extension  of  what  has  already  been  done  in  connection  with 
Fig.  i.  With  the  data  exhibited  in  Fig.  I  it  might  have  been  found  con- 
venient to  use  the  mean  as  the  origin  and  to  plot  the  frequency  with  respect 
to  deviations  from  the  mean.  Since  the  mean  is  in  this  case  7.25,  we  have 
the  following  set  of  deviations  and  corresponding  frequencies  to  plot : 


Deviations     

-3-25 

-2.75 

-2.25 

-1-75 

-1.25 

-0-75 

-0.25 

0.25 

0.75 

1-25 

J-75 

2.25 

2-75 

Frequencies  

i 

• 

8 

33 

70 

no 

176 

172 

124 

61 

32 

10 

2 

We  should  now  lay  off  the  positive  deviations  toward  the  right  from  the 
origin  O  (Fig.  2)  and  the  negative  deviations  toward  the  left  from  O.  The 
frequencies  should,  of  course,  be  plotted  upward  from  X'X,  just  as  in  Fig.  i. 
The  result  of  plotting  this  frequency  distribution  is  shown  in  Fig.  2.  This 
should  bring  home  to  the  reader,  who  is  not  very  familiar  with  the  use  of 
negative  numbers,  the  fact  that  negative  numbers  may  be  just  as  u  real " 
and  useful  as  positive  numbers. 

The  frequency  polygon  of  Fig.  2  does  not  differ  in  form  from  that  of 
Fig.  I.  It  is  only  differently  related  to  the  lines  of  reference  OX  and  OY. 

Graphical  meaning  of  median,  mean,  and  mode.  If  in  Fig.  i  we  select  on 
the  curve  a  point  whose  ordinate  divides  the  area  under  the  curve  into  two 
equal  parts,  the  abscissa  of  this  point  is  the  median  of  the  population.  The 


APPENDIX 


689 


abscissa  of  the  center  of  gravity  of  the  total  area  under  the  curve  is  the 
mean  of  the  population,  and  the  abscissa  of  the  highest  point  on  the  fre- 
quency curve  is  the  theoretical  mode  of  the  population. 


FIG.  2 

Graph  of  a  mathematical  function.  A  number^  is  said  to  be  a  mathematical 
function  of  a  number  x  if  to  assigned  values  of  x  there  correspond  definite 
values  oiy. 

Thus,  if  y  —  2.x,y\s  a  function  of  x, 
since  for  any  assigned  value  of  x  we 
can  compute  y.  In  general,  if  x  and_y 
are  connected  by  an  equation  each  is  a 
function  of  the  other.  The  study  of 
certain  functions  is  of  the  first  rate  in 
importance  in  the  mathematical  theory 
of  statistics,  and  this  is  much  facili- 
tated by  the  use  of  the  graph  of  the  X"— 
function  in  question.  We  therefore 
proceed  to  show  how  to  form  the  graph 
of  a  few  simple  functions  so  as  to 
give  the  general  notion  of  the  graph 
of  functions. 

Take  coordinate  axes,  as  in  Fig.  3, 
which  divide  the  plane  into  four  quad- 
rants.    If  the  abscissas  are  positive,  FIG.  3 
they  should  be  laid  off  to  the  right 

of  O  ;  if  negative,  they  should  be  laid  off  to  the  left  of  O.  The  ordinates,  if 
positive,  are  to  be  laid  off  upward  from  the  ^r-axis  ;  if  negative,  they  are  to  be 
laid  off  downward.  Then  whatever  two  numbers  (positive  or  negative)  are 
given  as  abscissa  and  ordinate,  the  corresponding  point  can  be  located. 


690 


APPENDIX 


Let  us  take  as  an  illustration  the  plotting  of  the  graph  of  y  =  2.x  +  4. 
Here  we  see  from  the  equation  that  corresponding  to  any  value  assigned 
to  x  we  get  a  value  of  y  equal  to  twice  x  plus  4.  The  corresponding  values 
are  as  follows : 


X 

o 

i 

2 

3 

4 

5 

- 

—2 

-3 

4 

-5 

y 

4 

6 

8 

10 

12 

14 

+  2 

O 

—2 

-4 

-6 

Locating,  in  Fig.  3,  the  points  corresponding  to  these  values,  and  draw- 
ing a  smooth  curve  through  them,  we  have  the  graph  of  the  function.  This 
graph  is  a  straight  line. 

We  leave  as  an  exercise  for  the  student  to  find  the  graph  of  y  =  xz.  For 
application  of  graph  of  function,  see  "Probability  Curve,"  Section  VI. 


SECTION   IV  — "SMOOTHING"  OF  FIGURES 

Sometimes  the  frequency  distribution  of  a  population  arranged  with 
respect  to  some  character  has  many  small  irregularities  which  arise  merely 
from  the  way  in  which  the  measurements  were  taken  and  grouped.  In 
such  a  case  a  process  called  "smoothing"  can  often  be  employed  to 
obtain  regularity.  A  noteworthy  instance  of  smoothing  is  to  be  seen  in  the 
adjusting  of  the  population  census  with  respect  to  age,  there  being  a  great 
many  more  people  who  report  their  ages  as  40  than  as  39  or  41.  In 
fact,  sometimes  the  unsmoothed  figures  show  one  half  more  people  of 
age  40  than  of  age  39  or  41.  It  is,  then,  manifestly  desirable  to  smooth 
these  census  returns  if  they  are  to  give  even  an  approximately  correct 
impression. 

In  representing  such  a  distribution  graphically  we  have  to  draw  a  smooth 
line  in  the  neighborhood  of  the  points,  but  not  necessarily  through  any  of 
them.  This  smooth  line  is  the  result  of  the  attempt  to  present  what  the 
distribution  would  be  if  the  causes  of  the  small  irregularities  could  be 
removed.  Sometimes  it  is  convenient  to  smooth  figures  without  resorting 
to  a  graph.  There  are  some  rather  refined  but  complicated  algebraic 
methods  l  of  doing  this,  but  in  general  a  very  simple  method  can  be  used. 
To  explain  this  method,  take  the  following  frequency  distribution  (which 
was  obtained  by  measuring  the  circumferences  of  995  ears  of  corn),  in  which 
the  groupings  into  |-inch  classes  are  not  well  selected. 


Inches  

4-5 

4-75 

5.0 

5-25 

5-5 

5-75 

6.0 

6.25 

6.5 

6-75 

7.0 

7-25 

7o 

7-75 

8.0 

8.25 

8-5 

Frequencies     .   . 

2 

4 

'3 

24 

20 

74 

125 

98 

181 

98 

208 

55 

67 

10 

it 

3 

2 

1  Darwin,  Philosophical  Magazine  and  Journal^  July,  1877. 


APPENDIX 


691 


It  may  be  well  to  explain  the  chief  source  of  this  irregularity.  This 
can  be  seen  by  observing  two  classes,  such  as  the  7-inch  class  and  the 
6. 75-inch  class.  As  the  measurements  were  recorded  to  the  nearest  tenth 
inch,  the  7-inch  class  includes  the  measurements  recorded  as  6.9,  7,  and 
7.1,  while  the  6.75-inch  class  includes  only  those  recorded  as  6.7  and  6.8. 
This  should  evidently  produce  a  biased  result.  Instead  of  making  a  new 
frequency  table  with  a  different  grouping,  we  may  substitute  for  each 
frequency  a  number  derived  by  smoothing.  This  smoothing  can  be  accom- 
plished by  substituting  for  each  frequency,  except  the  two  extreme  ones, 
the  mean  of  the  given  frequency  and  the  one  immediately  before  and 
the  one  immediately  after  it.  Thus,  for  frequency  of  ears  of  length  4.75 

2  +  4  +  13 

inches  we  should  substitute —  =  6£.  But  as  this  is  only  an  approxi- 
mation, we  may  as  well  take  the  nearest  integral  value,  or  6.  For  an  extreme 
frequency,  we  substitute  the  mean  (to  nearest  integer)  of  the  extreme  fre- 
quency taken  twice  and  the  adjacent  frequency  taken  once.  Thus,  for  the 

frequency  corresponding  to  length  4.5  inches  we  substitute  —  —  =  2§, 

or,  in  integral  numbers,  3.  It  is  sometimes  desirable  to  apply  this  process 
more  than  once  to  a  given  distribution  in  order  to  give  it  the  desired 
regularity. 

The  results  of  the  scheme  for  the  given  frequency  distribution  are  as 
follows : 


Inches  .  .  .  .   < 

4-5 

4-7S 

5-o 

5-2S 

5-5 

5-75 

6.0 

6.25 

6-5 

6-75 

7.0 

7.25 

7-5 

7-75 

8.0 

8.25 

8-5 

Unsmoothed      f 
frequencies     j 

2 

4 

!3 

24 

20 

74 

125 

98 

181 

98 

208 

55 

67 

10 

II 

3 

2 

ist  smoothed     J 
frequencies    "| 

3 

6 

M 

*9 

39 

73 

99 

'35 

126 

162 

I2O 

no 

44 

29 

8 

5 

2 

2d  smoothed     j 
frequencies     j 

4 

8 

T3 

24 

43 

70 

102 

1  20 

141 

138 

J3i 

9i 

61 

27 

14 

5 

3 

In  general  algebraic  terms,  if  vv  vv  •  •  •,  vn  are  the  marks  of  classes  and 
#  15  #2,  •  •  •,  an  the  corresponding  frequencies,  in  smoothing  the  tf's  we  should 
substitute  for  them  the  following  values  respectively : 


2  tf 


It  can  be  easily  seen  from  these  algebraic  expressions  that  the  arith- 
metic mean  of  the  measurements  is  scarcely  affected  at  all  by  smoothing, 
but  that  the  mode  is  sometimes  considerably  changed.  In  general,  the 
"standard  deviation"  (to  be  discussed  in  Section  VII)  is  but  slightly 
affected  by  smoothing. 


692  APPENDIX 

SECTION    V  — APPLICATION    OF    THE   THEORY   OF 
PROBABILITY 

The  reader  should  understand  thoroughly  that  what  is  commonly  known 
as  a  "  law  of  nature  "  is  a  generalization  based  upon  experience,  and  that  such 
a  law  cannot  be  proved  in  the  strictly  logical  sense,  but.  only  in  the  sense  of 
establishing  a  high  degree  of  probability  in  its  favor.  To  illustrate,  we  may 
take  one  of  the  best-established  facts  of  physical  science,  namely,  that  all  free 
bodies  are  attracted  by  the  earth.  The  evidence  for  this  statement  consists 
in  the  fact  that  the  thousands  and  even  millions  of  bodies  which  have  been 
observed  have,  without  exception,  followed  this  rule.  This  has  established 
a  very  high  degree  of  probability.  It  is  altogether  conceivable,  however, 
that  some  body  exists  which  would  be  repelled  by  the  earth.  Although 
experience  has  established  an  overwhelming  probability  against  such  an 
occurrence,  we  must  not  overlook  the  fact  that  experience  has  proved  the 
statement  only  in  the  sense  that  it  has  established  a  high  degree  of  proba- 
bility. It  has  done  this  and  can  do  nothing  more  than  this.  It  is  doubtful 
whether  any  person  living  has  seen  a  hundred  pennies  tossed  at  random, 
all  of  which  came  heads  up,  and  still  it  is  possible  that  this  might  happen. 
Even  if  no  one  has  seen  them  fall  with  all  heads  up,  we  are  clearly  not 
justified  in  concluding  that  there  will  always  be  some  heads  up  and  some 
tails  up.  If  a  thousand  pennies  be  tossed  at  random,  the  probability  that 
they  will  all  fall  heads  up  is  so  small  that  we  may  safely  say,  if  the  whole 
human  race  were  to  devote  a  generation  to  the  tossing  of  pennies,  a  thousand 
at  a  time,  there  would  still  be  a  very  small  probability  that  any  one  would 
toss  all  heads.  All  this  goes  to  show  that  certain  possible  events  have  such 
a  slight  probability  that  we  should  not  expect  them  to  happen  in  the  lifetime 
of  a  given  individual.  Just  so,  as  time  goes  on  and  observations  are  made  in 
greater  numbers,  exceptions  may  be  found  to  any  of  the  so-called  "  laws  of 
nature."  Such  exceptions  are,  however,  in  many  cases  exceedingly  unlikely. 

It  is  hoped  that  the  foregoing  paves  the  way  for  the  statement  that, 
while  in  this  subject  many  results  may  be  stated  in  terms  of  probabilities, 
these  results  do  not  differ  in  reliability  on  that  account  from  those  of  any 
other  science  based  on  experience.  If  a  thousand  pennies  be  tossed  at 
random,  there  is  nothing  more  uncertain  than  that  a  given  penny  will 
be  heads,  but  it  is  a  matter  of  common  experience  that  the  ratio  of  the 
number  of  heads  to  the  total  number  of  pennies  tossed  is,  in  general,  nearly 
one  half.  We  may  here  recall  the  statement  of  Section  I,  that  the  theory 
of  probability  is  needed  in  this  subject  because  we  deal  with  occurrences 
and  characters  of  such  a  nature  that  we  wish  to  make  statements  in  regard 
to  a  large  number  of  them  taken  together.  It  is  a  matter  of  common  experi- 
ence that  results,  such  as  averages  and  ratios  obtained  from  large  numbers 
of  cases,  are  nearly  stationary.  We  find  the  average  stature  of  a  thousand 
individuals  selected  at  random  from  a  large  population,  and  are  much  sur- 
prised if,  upon  taking  another  random  sample  of  a  thousand  from  the  same 


APPENDIX  693 

population,  their  average  stature  differs  materially  from  that  already  found. 
We  are  not  at  all  surprised  if  the  averages  are  substantially  equal.  There 
are,  no  doubt,  many  causes  which  influence  the  growth  of  each  individual 
differently,  but  when  they  are  all  taken  together  these  small  disturbances 
tend  to  counterbalance  each  other.  In  short,  it  is  regularity  in  large  num- 
bers which  we  expect.  While  it  may  be  common  sense  to  expect  this,  we 
shall  later  give  a  mathematical  measure  known  as  the  "  probable  error"  to 
indicate  what  deviations  we  should  expect  in  results  such  as  averages  derived 
from  a  random  sample.  This  discussion  leads  us  to  the  following  definition 
of  probability. 

Definition.  If,  in  the  long  run,  out  of  n  possible  cases  in  each  of  which 
an  event  occurs  or  fails  to  occur,  it  occurs  n\  times  and  fails  to  occur  n  —  n^ 
times,  the  probability  that  the  event  occurs  on  a  given  occasion  in  question 

is  — ,  and  the  probability  that  it  fails  to  occur  on  a  given  occasion  is • 

n  n 

In  framing  this  definition  we  idealize  our  actual  experience.  We  say 
the  probability  of  a  penny's  turning  up  heads  is  one  half.  This  may  be 
looked  upon  as  an  answer  to  the  following  question :  What  proportion  of 
the  pennies  tossed  should  we  expect  to  find  with  heads  turned  up  if  we 
should  continue  tossing  indefinitely  ? 

This  idealization,  for  purposes  of  definition,  is  analogous  to  the  idealiza- 
tion of  the  crude  chalk  mark  into  the  straight  line  of  geometry.  Since  the 

sum  of  the  probabilities  of  occurrence  and  failure  is  —  H =  I,  the 

n  n 

number  i  is  the  symbol  of  certainty.  The  expression  "  relative  frequency  " 
conveys  fairly  well  the  idea  of  probability. 

The  following  corollary  is  often  easier  to  apply  than  the  definition. 

Corollary.  If  the  entire  number  of  possible  cases  in  which  an  event  is  in 
question  can  be  analyzed  into  n'  cases,  each  of  which  is  equally  likely,  and 

m'  is  the  number  of  these  cases  in  which  the  event  occurs,  then  —  is  the 
probability  of  the  event. 

Thus,  in  tossing  two  pennies,  what  is  the  probability  that  one  will  be 
heads  and  one  tails  ? 

There  are  four  different  ways  in  which  the  pennies  may  fall :  Head  and 
tail,  tail  and  head,  head  and  head,  tail  and  tail.  Two  of  these  ways  lead 
to  the  occurrence  of  the  event.  Hence  f  =  \  is  the  desired  probability  of 
one  head  and  one  tail. 

Combination  of  probabilities.  The  probability  that  all  of  a  set  of  independ- 
ent events  will  occur  on  any  occasion  in  which  all  of  them  are  in  question  is 
the  product  of  the  probabilities  of  the  single  events. 

Proof.  Let/p/.,,  . . .,  pr  be  the  separate  probabilities  of  r  events.  Out 
of  a  great  number,  n,  of  cases,  the  first  will  happen  on  p^n  occasions.  Out 
of  these  the  second  will  happen  on  p2  (p^ri)  occasions.  Continuing  this 
process,  and  applying  the  definition  of  probability,  the  theorem  is  at  once 
established.  To  illustrate,  suppose  that  among  a  population  of  a  hundred 


694  APPENDIX 

thousand  people  thirty  thousand  are  vaccinated,  and  that  five  hundred  per- 
sons have  smallpox.  If  vaccination  has  no  influence  on  the  number  of  cases 
of  smallpox,  what  is  the  probability  that  a  person  will  be  both  vaccinated 
and  have  smallpox  ? 

Since  one  hundred  thousand  is  a  large  number,  we  may  give 

-^ =  —      =  probability  that  a  person  is  vaccinated ; 

I 00000         10 

=  probability  that  a  person  has  smallpox ; 


i ooooo      200 
3       i  3 


=  probability  that  a  person  is  both  vaccinated 


10     200        2000 

and  has  smallpox. 

Furthermore,  —  -  x  i  ooooo  =  150,  the  number  of  persons  we  should  ex- 
pect both  to  be  vaccinated  and  to  have  smallpox,  if  vaccination  has  no 
influence  on  the  number  of  cases  of  smallpox. 

Illustrations  of  probability.  Let  us  throw  out  upon  a  table  at  random  four 
pennies ;  what  is  the  probability  that  exactly  r  of  them  will  be  heads  and  the 
rest  tails  when  r  takes  values  o,  i,  2,  j,  4  ? 

(1)  Probability  that  o  will  be  head  and  4  tails  is     Q)4 

(2)  Probability  that  i  will  be  head  and  3  tails  is  4(J)4 

(3)  Probability  that  2  will  be  heads  and  2  tails  is  6(|)4 

(4)  Probability  that  3  will  be  heads  and  i  tail  is  4(^)4 

(5)  Probability  that  4  will  be  heads  and  o  tail    is  (|)4 

In  (2)  the  coefficient  4  appears  before  Q)4  because  with  four  coins  there 
are  four  different  combinations1  possible,  each  consisting  of  i  head  and  3 
tails.  Similarly  in  (3)  the  coefficient  6  appears  because  with  four  coins 
there  are  possible  six  combinations,  each  consisting  of  2  heads  and  2  tails. 

The  above  illustration  may  be  generalized  and  the  result  put  into  the 
following  form  : 

If  n  coins  are  thrown  upon  a  table  at  random,  the  probability  that  exactly 
r  of  them  will  be  heads  and  the  rest  tails  is  given  by  the  r+  ist  term  of 

the  binomial  expansion  I-  +  -  )  ;  that  is,  in  other  symbols,  "CV(?)"»  where 
the  symbol  "Cr  indicates  the  number  of  combinations  of  n  things  taken  r 
at  a  time. 

In  order  that  the  reader  may  more  fully  appreciate  the  greater  prob- 
ability of  getting  an  almost  equal  number  of  heads  and  tails  in  tossing 
pennies  than  of  getting  widely  different  numbers,  we  present  the  following 
table  for  n  =  999>  obtained  from  Que'telet  Sur  la  thdorie  des  probability. 

1  For  definition  of  a  combination,  see  text,  p.  511. 


APPENDIX 


695 


Columns  i  and  2  give  the  number  of  heads  and  tails  whose  probability 
is  in  question.  Column  3  gives  the  probability  of  exactly  the  number  of 
heads  and  tails  indicated  in  columns  I  and  2. 


I 
HEADS 

2 

TAILS 

3 
PROBABILITY 

i 
HEADS 

2 

TAILS 

3 
PROBABILITY 

499 

500 

9"C50o(!)999=  0.025225 

450 

549 

0.0001863 

490 

5°9 

999  6-5o9(.l)"9=  0.021069 

440 

559 

O.OOOO2O9 

480 

5T9 

999  Cf6i9(^)999=  0.011794 

43° 

569 

0.0000016 

470 

529 

999  C529a)999=  0.004423 

420 

579 

O.OOOOOOO4 

460 

539 

999  CWi)999  =0.001  1  10 

A  glance  at  the  table  shows  that,  in  the  long  run,  one  should  expect  499 
heads  and  500  tails  more  than  600,000  times  as  often  as  420  heads  and  579 
tails.  In  this  connection  it  is  interesting  to  inquire  into  a  case  mentioned 
on  page  692,  namely,  the  probability  of  getting  all  heads  in  a  single  throw 
of  a  thousand  pennies.  This  probability  is 


an  integer  containing  302  figures) 

and  the  statement  made  on  page  692  as  to  the  human  race  (population 

1,500,000,000)  devoting  itself  to  tossing  pennies  is  clearly  a  safe  statement. 

The  results  in  the  above  table  may  well  be  exhibited  graphically  (Fig.  4). 


490500         509 


696 


APPENDIX 


If  we  had  taken  all  the  intermediate  integers  from  499  with  500  to  440 
with  559,  we  should  have  had  ten  times  as  many  points  which  would 
arrange  themselves  along  the  curve  in  Fig.  4.  By  increasing  the  number 
of  coins  and  decreasing  the  horizontal  scale,  we  can  get  the  points  as 
close  together  as  we  please.  This  curve  in  Fig.  4  is  the  so-called  prob- 
ability curve  and  it  approaches  very  nearly  the  curve  of  error,  or  normal 
frequency  curve,  which  we  are  now  prepared  to  discuss. 


SECTION  VI— NORMAL   PROBABILITY   CURVE 

It  has  been  found  that  the  frequency  curves  of  a  great  many  biological 
measurements  follow  a  curve  variously  known  as  the  "  probability  curve," 
"normal  probability  curve,"  "curve  of  error,"  or  "normal  frequency 
curve."  In  particular  it  is  known  as  the  "curve  of  error,"  because  if 
errors  which  an  observer  makes  in  a  refined  set  of  direct  measurements 
on  a  given  quantity  be  plotted  as  abscissas,  the  corresponding  ordinates 
of  points  on  this  curve  represent  the  frequencies  or  probabilities  of  the 
errors, 

r 


The  general  form  of  the  curve  is  shown  in  Fig.  5.  The  origin  is  taken 
at  the  mean.  Then,  if  any  mark  of  a  class  is  above  the  mean,  its  devia- 
tion is  positive,  and  it  would  be  plotted  to  the  right  from  the  origin  O,  while 
if  the  mark  of  a  class  is  less  than  the  mean,  its  deviation  is  negative,  and 
it  would  be  plotted  to  the  left  from  O.  For  the  benefit  of  those  who  are 


APPENDIX 


697 


familiar  with  the  calculus,  the  derivation  of  this  curve  will  be  treated  in 
a  footnote,1  but  a  complete  understanding  of  this  footnote  is  not  necessary 
for  reading  what  follows. 

While  the  equation  of  this  curve  has  been  derived  in  many  different 
ways  by  arguments  based  on  a  few  assumptions  as  to  the  nature  and  causes 
of  deviations  from  the  mean,  it  must  be  granted  that  these  assumptions  are 
of  such  a  nature  that  experiment  is  an  important  test  as  to  whether  a 
frequency  distribution  is  of  this  type.  The  reader  should  be  on  his  guard 
against  the  mistake  that  deviations  from  the  mean,  in  all  classes  of  measure- 
ments, follow  closely  this  law  of  frequency.2  In  fact,  Pearson  has  found 
that  in  many  cases  frequency  distributions  obtained  in  biological  study  can- 
not be  so  well  fitted  by  the  normal  curve  as  by  what  he  calls  generalized 
probability  curves,  which  take  "  skewness  "  and  limit  of  range  into  account. 
These  curves  lead  us  into  mathematical  complications  which  cannot  be  well 
treated  here,  but  it  may  be  remarked  that  he  obtains  these  curves  from  the 
point  binomial  (p  +  q}n,  where/  +  q  —  I,  but p  ^  g,  and  from  a  hypergeo- 
metric  series. 

1  While  Gauss,  Laplace,  Quetelet,  Herschel,  and  other  great  mathematicians  have  derived 
the  equation  of  the  normal  curve,  and  all  agree  in  the  result,  they  differ  widely  as  to  hypoth- 
eses upon  which  they  base  the  derivations. 

We  present  here  a  derivation  based  upon  the  hypothesis  (see  Pearson,  Philosophical 
Transactions,  CLXXXVI,  A,  pp.  343-381)  that  the  normal  curve  represents  a  function 
y  —  <f>(x)  which  has  a  certain  slope  condition  obtained  from  the  point  binomial  polygon 
(i  +  i)  m  (see  Fig.  4)-  This  slope  condition  may  be  stated  as  follows  : 

slope  of  side  _  2  mean  abscissa  of  side 

mean  ordinate  of  side  2  a2 

the  jy-axis  being  the  axis  of  symmetry  and  the  <r  being  the  same  for  all  sides. 
In  calculus  form,  this  condition  would  be 

dy        _  2x 
ydx~       20-2' 

_  — 
Integrating,  y  =  ke    2<r2- 

The  constant  k  can  be  determined  by  finding  the  total  area  under  the  curve  and  equating 
this  to  the  total  population  n  which  the  area  represents.  This  gives 


and  the  final  form  of  the  equation  of  the  normal  curve  is 


in  which  <r  will  later  be  shown  to  be  what  we  shall  call  the  "standard  deviation"  and 
e  —  2.718  •  •  •,  the  base  of  Napierian  logarithms. 

If  equation  (i)  is  to  give  probabilities  instead  of  frequencies,  we  must  replace  n  by  i  in 
equation  (i). 

2  For  fulfillment  of  the  normal  law  in  nature,  see  Edgeworth,  Statistical  Journal,  Jubilee 
Number,  1885,  p.  188. 


698  APPENDIX 

However,  the  normal  curves  give,  in  general,  at  least  a  valuable  first 
approximation,  and  we  shall  follow  the  usual  method  of  employing  statis- 
tical constants  derived  from  this  curve  ;  for  these  constants  are  significant, 
even  if  the  distribution  is  not  normal.1 

Area  under  the  probability  curve  has  an  important  meaning.  If  we  select 
unit  area  as  explained  in  Section  III,  the  area  represents  the  total  population, 
and  the  area  between  the  two  ordinates,  the  curve,  and  .r-axis  represents  the 
number  of  variates  between  these  ordinates.  If  we  look  upon  the  curve  as 
representing  probabilities  instead  of  frequencies  our  horizontal  scale  is 
unchanged  but  our  vertical  scale  must  be  multiplied  by  the  total  popula- 
tion. Thus,  if  the  population  is  800,  as  in  the  case  of  Fig.  i,  we  should  say 
that  what  there  represented  unity  should  be  multiplied  by  800  in  order  that 
it  shall  represent  unit  of  probability.  Then  the  entire  area  under  the  curve 
will  be  unity,  and  the  area  between  two  ordinates,  the  curve,  and  jr-axis  is 
simply  the  probability  that  a  variate  selected  at  random  would  lie  within 
this  interval.  f  . 

SECTION  VII  — PROBABLE  ERROR  AND  STANDARD 
DEVIATION 

If  we  have  estimated  the  population  of  a  city  at  100,000  and  have 
good  reason  to  think  that  the  chances  are  even  that  this  is  correct  within 
1000,  we  give  much  more  information  by  stating  that  the  population  is 
100,000  ±  1000  than  by  giving  merely  the  figures  100,000  and  leaving  the 
reader  entirely  in  doubt  as  to  the  accuracy  of  the  determination. 

In  describing  a  frequency  distribution  the  average  gives  absolutely  no 
idea  as  to  whether  deviations  are  large  or  small,  —  nothing  in  regard  to  the 
spread  of  the  distribution.  It  is  the  object  of  the  "standard  deviation"  to 
be  descriptive  of  this  variability,  and  it  is  the  object  of  the  so-called 
"  probable  error  "  to  indicate  what  confidence  is  to  be  placed  in  statistical 
results.  The  use  which  has  been  made  of  both  "standard  deviation"  and 
«  probable  error  "  makes  it  unnecessary  to  dwell  longer  on  this  point,  but 
it  is  our  purpose  here  to  show  how  the  formulas  used  in  the  text  are  derived. 

Probable  error  of  a  single  variate.  The  probable  error  of  a  single  vat-tat e 
of  a  population  is  defined  as  that  departure  from  the  mean,  on  either  side, 
within  which  exactly  one  half  the  variates  are  found. 

By  the  use  of  the  probability  curve  (Fig.  6)  the  probable  error  may 
easily  be  explained  geometrically  when  we  look  upon  the  entire  area  under 
the  curve  as  representing  the  total  population.  In  Fig.  6  we  draw  two 
ordinates,  ST  and  S'T*,  equally  distant  from  the  mean,  and  such  that  one 
half  of  the  entire  area  under  the  curve  lies  between  them,  in  other  words, 
is  bounded  by  the  curve,  the  .r-axis,  ST,  and  S'T'.  Then  ±  OS  represents  the 
probable  error  of  a  single  variate.  If  we  should  use  a  single  variate  selected 
at  random  to  represent  the  population  it  is  an  even  chance  that  that  single 
variate  would  be  less  or  more  than  OS  from  the  best  value. 

1  See  Yule,  Proceedings  of  the  Royal  Society,  LX,  477-489. 


APPENDIX 


699 


An  approximate  value  for  the  probable  error  of  a  single  variate  in  any 
population  may  be  easily  obtained  in  the  following  manner  : 
i  .  Arrange  the  variates  in  the  order  of  magnitude. 

2.  Count  one  fourth  of  the  variates  of  least  measurements  and  note  the 
measurement  of  the  upper  one  of  these   variates.     Let  u  represent  this 
measurement. 

3.  Count  one  fourth  of  the  variates  of  greatest  measurements  and  note 
the  measurement  of  the   lower  of  these  variates.     Let  v  represent  this 
measurement. 

4.  Then  -  gives  the  probable  error  of  a  single  variate. 
The  formula  for  the  probable  error  in  a  single  variate  is 


Es  =  0.6745  \, 

where  S-*"2  means  the  sum  of  the  squares  of  the  deviations  from  the  mean 
and  n  is  the  number  of  variates.    The  conception  of  the  probable  error  of 

Y 


a  single  variate  is  of  value  because  it  aids  in  the  derivation  of  the  probable 
error  of  other  important  results.     The  formula  for  the  standard  deviation 

is  (page  429)  A/--1   ,  so  that  the  probable  error  of  a  single  variate  is  obtained 

from  the  standard  deviation  of  the  population  by  multiplying  the  standard 
deviation  by  0.6745. 


700  APPENDIX 

As  has  been  pointed  out  in  the  text,  the  standard  deviation  gives  a  good 
idea  of  the  spread  of  the  distribution.  From  the  accompanying  footnote  * 
we  are  now  in  a  position  to  appreciate  its  mathematical  significance.  It 


-  — 
is  the  <r  in  the  equation^  =  — j=  e   2  r    of  the  normal  probability  curve, 

and  bears  a  similar  relation  to  the  probability  curve  that  the  radius  of  a 
circle  bears  to  the  circle.  If  <r  is  small  the  probability  curve  is  crowded 
together  so  as  to  resemble  curve  A  in  Fig.  7,  while  if  <r  is  large  it  is  spread 
out  so  as  to  resemble  curve  B  in  Fig.  7. 

Hence  the  standard  deviation  along  with  the  mean  completely  describes 

VV^2 
,  which  is  thus  a 
n 

perfect  measure  of  variability  for  a  normal  distribution,  is  a  good  measure 
of  variability  when  the  distribution  is  not  normal,  but  it  is  not  completely 
descriptive  of  the  population. 

Another  measure  of  variability  is  sometimes  used  which  consists  simply 
in  taking  the  arithmetical  average  of  the  n  deviations,  —  these  deviations 
being  given  the  positive  sign. 

1  The  probability  that  a  system  of  n  variates  fall  in  intervals  x^  to  #,  +  A#,  x2  to  xa  +  Ax, 
. . .  xn  to  xn  +  A#  is  given  by 

P=  — *       g'Zt* '       /^... l       e~^. 

<rV27T  <rV27T  0-V27T 

This  may  be  written  more  briefly  as 

_2f2 

P=  —      — -e   2<r2(A*)». 

<r«  (2  TT)? 

For  a  given  set  of  deviations  which  occur,  <r  should  be  selected  so  as  to  make  the 
probability  P  a  maximum.  ,„ 

Equating  the  first  derivative  —  to  zero,  we  obtain 

CLl  I  „  --2          I     „.  I  M  _o 


da  ff^  "  (r«  +  i 


Now,  by  means  of  integral  calculus,  tables  are  formed  of  the  area  included  by  the  curve 


the  #-axis,  and  any  two  ordinates  at  equal  distances  ±  a  from  the  mean.  Such  a  table  with 
the  argument  -  is  found  in  Davenport's  Statistical  Methods,  second  edition,  pp.  119-125. 

This  table  shows  that  x 

-  =  0.6745  (0 

when  just  one  half  of  the  area  under  the  curve  is  included  as  described  above.  By  definition, 
the  particular  value  of  x  given  by  (i)  is  called  the  probable  error  in  a  single  variate,  and  we 
shall  represent  it  by  Es. 

Hence,  E,  =  .6745  <r- 

2  See  Galton,  Natural  Inheritance,  p.  62. 


APPENDIX 

The  formula  for  this  is  simply 


701 


where  the  marks  |  j  indicate  that  the  numbers  should  all  be  taken  with  the 
positive  sign. 

This  measure  of  variability  is  usually  known  as  the  average  deviation. 

As  to  the  relative  merits  of  these  two  measures  of  variability,  the  stand- 
ard deviation  is  to  be  preferred.  Its  relation  to  the  probability  curve  as 
indicated  above  gives  it  special  favor  mathematically,  although  a  geometric 
meaning  may  also  be  given  to  the  average  deviation. 

Probable  error  of  the  mean.  Since  in  natural  science  results  are,  in  gen- 
eral, based  on  averages,  we  are  more  directly  interested  in  the  probable 
error  in  the  mean  than  in  the  probable  error  of  a  single  variate,  although 


the  latter  conception  is  desirable  as  a  basis  for  understanding  the  former. 
We  can  best  discuss  the  probable  error  in  the  mean  by  beginning  with  an 
illustration. 

Suppose  that,  in  determining  the  average  stature  of  a  male  population 
consisting  of  a  million  individuals,  we  select  at  random  groups  of  a  thou- 
sand each.  We  could  then,  in  all,  have  available  a  thousand  such  groups 
using  no  individual  twice.  It  is  an  axiom  of  statistics,  as  we  have  already 
explained,  that  the  mean  statures  obtained  from  each  of  these  groups  will 


702  APPENDIX 

differ  but  slightly  from  each  other,  but  if  the  measurements  are  sufficiently 
accurate  there  will  be  some  differences.  If  we  should  find  the  mean  of 
these  means  (we  may  call  it  the  second  mean)  we  could  plot  a  frequency 
curve  of  the  distribution  of  means  just  as  we  have  for  the  deviations 
of  the  original  variates.  Of  course  this  curve  would  be  much  crowded 
together,  like  A  of  Fig.  7.  To  make  this  general,  with  a  very  large  popu- 
lation, and  with  n  in  each  group  instead  of  1000,  the  following  result  is 
obtained  : 

If  Es  is  the  probable  error  of  a  single  variate,  that  of  the  mean  of  ;/ 
variates  is 

F        2- 

EM     V«' 

that  is,  to  find  the  probable  error  of  the  mean,  divide  the  probable  error 
of  a  single  variate  by  the  square  root  of  the  number  of  variates. 

Probable  error  in  standard  deviation.  Taking  up  again  the  million  cases 
of  stature  divided  into  a  thousand  groups  as  an  illustration,  supposing  that 
the  standard  deviation  of  each  of  these  thousand  groups  be  found,  we 
should  see  that  they  differ  but  slightly.  However,  if  the  computations  and 
measurements  be  very  refined  there  will  be  deviations.  These  standard 
deviations  constitute  a  frequency  distribution  whose  standard  deviation 
can  be  found,  and  the  probable  error  of  the  standard  deviation  can  be 
obtained  just  as  we  have  shown  in  the  case  of  a  single  variate. 

Generalizing  this  so  as  to  have  a  very  large  number  of  groups  each  con- 
taining n  variates  taken  as  a  sample  to  represent  the  population,  the  prob- 
able error  of  the  standard  deviation  is 


that  is,  to  find  the  probable  error  in  the  standard  deviation,  divide  the 
probable  error  in  the  mean  by  V2. 

Formulas  for  probable  error  in  some  important  statistical  constants.  Enough 
has  now  been  said  to  give  the  conception  of  the  probable  error  in  any 
statistical  determination  and  a  general  notion  of  the  methods  by  which 
formulas  for  the  probable  error  are  derived. 

It  is  scarcely  necessary  to  remark  that  the  probable  error  does  not  take 
into  account  evident  mistakes  either  of  observation  or  computation.  We 
are  assuming  that  these  have  been  eliminated.  It  has  to  do  with  errors 
(deviations)  due  to  an  indefinitely  large  number  of  unassignable  causes 
such  that  the  errors  are  distributed  according  to  the  laws  of  probability. 

It  seems  unnecessary  to  continue  the  discussion  of  probable  error  in 
other  determinations,  but  it  does  seem  well  to  collect  together,  for  purposes 
of  reference,  the  formulas  for  the  probable  error  in  some  of  the  most 
important  statistical  constants. 


APPENDIX  703 

In  what   follows 

a-  is  to  represent  the  standard  deviation  ; 
n  is  to  represent  the  number  of  variates  ; 
c  is  to  represent  the  coefficient  of  variability ; 
r  is  to  represent  the  coefficient  of  correlation. 

1.  Es  —  0.6745  °"  —  probable  error  in  a  single  observation. 

Ef       0.6745  °" 

2.  EM  =  —:=  = •= —  =  probable  error  in  the  mean. 

v«  V// 

EM      0.6745  °" 

3.  E    —  -7=  = —     —  probable  error  in  standard  deviation. 

V2         V2  n 

4.  Ec  =  •  '  . —       i  +  2( )     2  =  probable  error  in  coefficient  of  varia- 

v2«  L     V'°°/J       bility 

0.6745  ^ 
= . —     approximately,  if  C\s  not  greater  than  10  per  cent. 

V2# 

0.6745  0  —  ?"*) 

5.  Er  —  —  -    =  probable  error  in  coefficient  of  correlation. 


6.  ER  =  — \l —    —  =  probable  error  in  the  regression  coefficient 

(Ta  *  11 


SECTION  VIII— CORRELATION    THEORY 

Definition.  Two  measurable  characters  of  an  individual,  or  of  related 
individuals,  are  said  to  be  correlated  if  to  a  selected  series  of  sizes  of  the  one 
there  correspond  sizes  of  the  other  whose  mean  values  are  functions  of  the 
selected  values.  The  word  "  sizes,"  here  used,  should  be  taken  to  mean 
"  numerical  measure." 

For  the  sake  of  concreteness  and  simplicity,  we  may  think  of  measuring 
the  correlation  of  sons  with  respect  to  their  fathers.  To  render  the  above 
definition  in  symbolic  language  and  to  develop  the  method  of  determining 
the  function  mentioned  in  the  definition  are  the  first  points  in  the  application 
of  mathematics  to  the  theory  of  correlation.  For  this  purpose,  let  x  and/ 
represent  variables  such  that y  =  <f>(x)  gives  the  mean  value  oiy  correspond- 
ing to  a  selected  x.  Then  the  problem  is  to  determine  <£(X). 

Suppose  the  following  system  of  corresponding  values  results  from 
measurement:  (x',y'},  (x",y"},  •••,  (x<"\  _y(;/)),  where  n  is  a  very  large 
number  indicating  the  population  of  fathers  and  corresponding  sons. 
These  observations  are  said  to  form  a  total  population  or  universe  of 
observations.  As  it  will  be  more  convenient  to  deal  with  the  deviations 
of  the  observations  from  their  mean  value  than  with  the  measurements 
themselves,  let  (/r1,.)/1),  (^'Ja)'  ' '  '>  (•*»»  /»)  rePresent  the  deviations  of 


704 


APPENDIX 


the  observations  from  their  mean  value.     These  deviations  may  be  con- 
veniently represented  with  respect  to  coordinate  axes  (Fig.  8). 

By  the  range  along  the  ;r-axis  we  shall  mean  such  an  interval  that  ordi- 
nates  drawn  at  the  extremities  of  the  interval  include  between  them  the 
total  population.  Thus,  in  Fig.  8,  the  range  is  taken  from  a  to  b.  This 
range  may  well  be  divided  into  some  number,  say  s,  of  equal  parts,  each 
of  width  AJT,  by  ordinates  at  the  points  of  division.  If  we  let  x{,  x£,  •  •  •, 
xs'  be  the  abscissas  of  the  feet  of  the  ordinates  through  the  middle  points 
of  the  s  classes,  we  shall  call  these  the  marks  of  the  classes  of /'s.  The 
values  of  y  which  belong  to  a  given  class  of  x  are  said  to  form  a  j-array. 


A'- 


X 


X 


•A' 


x 


x 


X 


X 


r 

FIG.  8 


Let  the  crosses  (x)  in  Fig.  8  represent  the  means  of  the  j's  in  each  of 
the  .r-arrays.  If  correlation  exists,  these  means  do  not  lie  at  random  over 
the  field,  but  arrange  themselves  more  or  less  in  the  form  of  a  smooth 
curve  called  the  "  curve  of  regression."  This  curve  is  a  crude  picture  of  the 
function  which  defines  the  correlation  of  the  ^-character  relative  to  the 
^-character.  Experience  has  shown  that,  in  many  sets  of  measurements, 
this  line  is  approximately  a  straight  line.  For  this  reason,  and  for  sim- 
plicity, the  line  subjected  to  the  condition  that  the  sum  of  the  squares  of  the 
deviations  (measured  parallel  to  the  _y-axis  and  weighted  with  number  of 
points  in  array)  of  the  means  from  it  shall  be  a  minimum,  is  called  the 
"line  of  regression."  When  the  means  lie  exactly  on  the  line  the  degres- 
sion is  said  to  be  "  truly  linear." 


APPENDIX 


705 


The  algebraic  details  of  subjecting  a  line  to  this  minimal  condition  are 
well  known  to  those  familiar  with  the  method  of  least  squares.  The  equa- 
tion of  the  resulting  line  is 


where  <rx  is  the  standard  deviation  of  the  population  with  respect  to  the 
^-character,  cr,,  is  the  standard  deviation  with  respect  to  the  j-character, 
and  r  is  the  correlation  coefficient  given  by 


where  the  summation  is  extended  to  every  two  corresponding  variates  of 
the  population. 

Similarly,  the  regression  of  the  ^-character  with  respect  to  the  ^-charac- 
ter is  given  by 

*  =  "%/•  <2> 

It  should  be  noted  that  (2)  cannot  be  obtained  from  (i)  by  solving  for 
x  in  equation  (i). 

Standard  deviation  of  arrays.    Suppose  that  the  regression  is  truly  linear, 

so  that  the  means  of  the  ^/-arrays  fall  on  the  linej  =  r^—,  and  furthermore 

that  the  standard  deviations  of  all  parallel  arrays  are  equal.    Then  the 
standard  deviation  of  any  array  must  be  given  by 


n 
where  the  summation  extends  to  the  entire  population. 


+ 
n 


=  <r/  -  2  r  V/  +  rV/ 

=  <r/(i-r>).  (3) 

Hence  the  standard  deviation  of  a  j-array  is  obtained  from  the  stand- 
ard deviation  <ry  of  the  total  population  with  respect  to  the  ^-character  by 
multiplying  o>  by  Vi  —  r2. 

Since  the  first  number  of  (3)  is  a  sum  of  squares  divided  by  n,  the 
second  number  must  be  positive.  Hence 

—  \<r<  i. 

This  shows  that  our  correlation  coefficient  must  take  values  between  +  I 
and  —  i . 


706  APPENDIX 

If  ;-  =  -f  i,  all  the  individual  points  of  the  population  will  lie  on  the  line 
of  regression,  and  we  can  therefore,  when  one  character  is  given,  tell 
exactly  what  the  associated  character  is  in  magnitude.  In  this  case  the 
correlation  is  said  to  be  perfect  positive  correlation.  Similarly,  if  r  =  —  i, 
the  correlation  would  be  perfect  negative  correlation. 

Three  variables.  The  theory  of  correlation  is  easily  extended  to  apply  to 
more  than  two  variables.  For  example,  we  might  investigate  the  correlation 
of  the  statures  of  sons  with  respect  to  the  statures  of  both  parents.  This  is 
the  case  of  biparental  inheritance  treated  in  the  text,  page  529,  and  the  for- 
mulas there  used  must  be  special  cases  of  those  which  we  are  about  to  derive 
for  giving  the  most  probable  value  of  a  variable  z  where  z  is  the  numerical 
value  of  a  character  correlated  with  characters  of  measurements  x  and  y. 

Suppose  that  the  following  system  of  corresponding  deviations  from  the 
means  have  resulted  from  measurement:  (x^y^z^  (xv yvz^  (x^y**  **)* 
.  .  .  ,  (xn,yniStJ).  Represent  these  measurements  with  respect  to  coordinate 
axes  in  three  dimensions.  These  axes  are  to  be  taken  at  right  angles  to 
each  other,  as  is  conventional  in  analytic  geometry,  and  may  be  referred 
to  as  the  x,  y,  and  z  axes.  It  now  requires  two  letters  to  mark  an  array  of 
z's.  We  shall  call  (.r/,  j/)  the  mark  of  a  class.  Now  imagine  the  means 
plotted  for  every  ^-array.  If  correlation  exists,  these  means  will  not  lie  at 
random  in  space,  but  will  arrange  themselves  approximately  on  a  surface 
called  the  "  surface  of  regression."  The  equation  of  a  surface  is  of  the  form 
z=f(X)y}.  We  shall  consider  only  the  case  where  this/1  function  is  of 
the  first  degree,  for  the  same  reasons  that  we  considered  only  the  case  of 
a  first  degree  function  in  the  case  of  correlation  of  two  variables. 

It  results  that  the  required  function  is 

*  =  r*"  ~  yiyz~x  +  Ty\  ~r*MrSy=y*  0) 


where  ryz  is  the  correlation  coefficient  between  the  y-  and  ^-characters,  and 
similar  meanings  are  to  be  given  to  the  other  r's,  as  indicated  by  the  sub- 
scripts. This  equation  gives  the  mean  value  of  the  ^--arrays  corresponding  to 
given  x  andj,  if  they  can  be  given  by  a  linear  function.  If  they  cannot  be 
accurately  given  by  a  linear  function,  this  equation  must  merely  be  looked 
upon  as  giving  a  first  approximation. 

Standard  deviation  of  arrays.  If  the  equation  (i)  be  used  to  estimate  the 
value  of  the  ^-character  corresponding  to  a  selected  x  and  y,  we  have  the 
square  of  standard  deviation  of  each  ^-array  about  this  estimated  value 
given  by  the  expression 


^  ) 


as  an  average  value,  where  the  summation  extends  to  all  the  observations ; 
and 

rxg  -  rxy  ryi  <rg  ryg  -  rxz  rxy  <rx 

-^-~,        and         *  =  ^         ;rW- 


I  -  r. 


APPENDIX  707 

When  expanded  and  expressed  in  terms  of  r's  and  <r's,  (2)  becomes 


The  formulas  used  in  the  text  in  discussing  biparental  inheritance  are 
special  cases  of  (i)  and  (3)  just  derived.  This  may  be  verified  by  making 
the  following  substitutions  : 

Put  x  =  hvy  =  h^  2  =  hz,  ryz  =  r2,  rxx  =  rv  rxy  -  rs,  a-*  =  <r3,  vx  =  <rv 
Then  in  the  new  notation  (i)  becomes 

Since  in  the  case  discussed  in  the  text  the  parents  were  taken  equi- 
potent,  rx  =  r2,  and  by  making  this  substitution  in  (4)  we  get 


which  is  the  formula  used  in  text.    Likewise,  if  we  make  these  substitutions 
in  (3),  we  get  for  the  variability  of  an  array  of  sons 


2.r 


which  is  the  formula  used  in  the  text. 

More  than  three  variables.  It  is  easily  seen  that  the  methods  employed 
in  the  case  of  two  and  three  variables  can  be  extended  to  any  number  of 
variables.  However,  the  complexity  of  the  algebraic  expressions  becomes  so 
great  that  it  does  not  seem  well  to  present  a  more  extended  discussion  here. 
For  the  general  case  of  any  number  of  variables,  the  reader  with  consider- 
able mathematical  training  is  referred  to  the  treatment  by  Karl  Pearson  in 
the  Philosophical  Transactions  of  the  Royal  Society,  A,  CLXXXVII,  1896, 
and  A,  CC,  1903.  In  the  papers  just  referred  to  the  general  expression  is 
also  given  for  the  variability  of  an  array  in  the  case  of  any  number  of 
variables.  It  is  from  this  general  expression  that  the  formula  used  in  the 
text  for  the  variability  of  an  array  of  offspring  after  n  generations  of 
selection  is  derived. 

Formula  for  the  correlation  coefficient  r  which  is  better  adapted  to  numer- 
ieal  calculation.  In  the  first  place,  the  calculation  of  the  standard  devia- 
tions of  both  systems  of  variates  should  be  done  by  the  shorter  method 
presented  on  page  429. 


708  APPENDIX 

The  value  obtained  for  r  on  page  705  is 


where  x  and  y  represent  deviations  from  the  means,  and  the  summation  is 
extended  to  every  pair  of  corresponding  deviations.  The  calculation  of 

^xy 

-  can  be  much  shortened  by  an  equivalent  formula  which  we  shall 
*fi<r 

now  derive.  Let  Gx  and  Gy  represent  class  marks  near  the  means  of  the 
systems  of  variates  indicated  by  the  subscripts,  and  Cx,  Cy  corrections  to 
these  class  marks  which  give  the  correct  mean  values  so  that 

Afx  =  Gx  +  Cx  , 

My       =       Gy        +        Cy      . 

Let  x'^y'  represent  deviations  from  Gx  and   Gy  which  correspond  to 
deviations  x,  y  from  the  mean.    Then 


Cx)  -  Cx^(y  +  Q 


n 
This  is  a  formula  much  better  adapted  to  computation  than  the  formula 


n<rx<ry 

Its  application  is  shown  in  the  text,  page  465. 

SECTION   IX  — RANDOM  SAMPLES 

We  know  full  well  that  we  cannot,  in  general,  measure  all  the  individ- 
uals of  a  race  or  population  whose  characteristics  we  wish  to  describe.  We 
are  obliged  to  get  our  information  and  to  construct  our  science  by  the 
selection  and  examination  of  samples  taken  at  random  from  a  large  group 
of  individuals.  To  illustrate,  it  is  not  practicable  to  measure  the  stature, 
nor,  in  general,  any  other  character  of  all  the  adults  in  the  United  States. 
We  must  be  content  to  deal  with  a  reasonably  small  number  that  will  make 
the  measurements  a  feasible  undertaking. 

An  investigator  is  always  concerned  about  the  number  of  variates  which 
must  be  measured  in  order  that  confidence  may  be  placed  in  his  results. 


APPENDIX  709 

For  instance,  he  asks,  Of  how  many  ears  of  corn  taken  at  random  must 
I  measure  the  length  in  order  to  obtain,  to  a  certain  desired  degree  of 
accuracy,  the  variability  of  the  corn  from  which  selection  is  made  ?  Must 
I  measure  fifty,  a  hundred,  or  a  thousand  ears  ?  Again,  how  many  variates 
must  I  take  to  give  a  reliable  determination  of  the  mean  ? 

Similarly,  in  any  correlation  study  he  will  be  concerned  with  the  num- 
ber of  variates  he  must  take  in  order  to  present  a  trustworthy  determina- 
tion of  the  correlation  coefficients. 

While  these  questions  cannot  be  answered  in  advance  for  all  kinds  of 
populations,  it  is  the  object  of  this  section  to  give  some  assistance  to  the 
inquiring  investigator  in  forming  a  judgment  in  this  matter.  The  best 
measure  thus  far  devised  upon  which  to  base  a  judgment  is  the  so-called 
"  probable  error." 

So  far  as  the  mean  is  concerned,  it  has  been  seen  that  the  probable 
error  of  a  single  variate  may  be  obtained  approximately  by  counting,  and 
that  the  probable  error  in  the  mean  is  obtained  from  that  of  a  single  vari- 
ate by  dividing  by  the  square  root  of  the  number  of  variates.  This  process 
can  often  be  applied  in  a  rough  way  before  much  labor  has  been  put  on  a 
problem,  and  it  becomes  a  useful  guide  where  the  mean  alone  is  in  question. 
It  should  be  remembered  that  the  probable  error  in  any  result  is,  in  gen- 
eral, inversely  proportional  to  the  number  of  observations. 

A  method  similar  to  that  just  explained  for  the  mean  can  be  used  to 
find  the  approximate  value  of  the  probable  error  of  the  standard  deviation, 
since  the  probable  error  of  _the  standard  deviation  is  obtained  from  that  of 
the  mean  by  dividing  by  VJ. 

As  for  the  coefficients  of  variability  and  correlation,  the  following  tables 
show  the  probable  errors  corresponding  to  values  of  the  coefficient  of  varia- 
bility from  i  per  cent  to  25  per  cent,  with  numbers  of  variates  from  25  to 
1000,  and  the  probable  errors  of  the  correlation  coefficient  for  values  from 
o  to  i,  with  numbers  of  variates  from  25  to  1000. 

If,  then,  we  have  an  approximate  notion  as  to  the  value  of  one  of  these 
coefficients,  we. can  find  from  the  table  the  probable  error  corresponding 
to  a  certain  number  of  variates. 

To  illustrate  the  use  of  these  tables,  suppose  that  we  know  in  advance 
that  the  coefficient  of  variability  is  in  the  neighborhood  of  20  per  cent ; 
then  with  a  hundred  variates  we  see  from  the  tables  that  the  probable  error 
would  be  approximately  i  per  cent,  while  with  five  hundred  variates  it  would 
be  only  0.44  per  cent.  We  thus  decide  upon  the  number  of  variates  by  the 
magnitude  of  the  probable  error  and  the  degree  of  accuracy  desired  in  our 
results. 

Probable  error  in  estimate  of  probability  from  a  limited  number  of  obser- 
vations. While  it  has  been  said  that,  in  a  general  way,  the  accuracy  of  a 
statistical  result  increases  as  the  square  root  of  the  number  of  observations, 
this  rule  is  often  difficult  to  apply,  and  is  an  inadequate  test  in  many 
important  cases. 


710 


APPENDIX 


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712  APPENDIX 

A  common  and  important  class  of  statistical  deductions,  which  should 
receive  very  critical  examination,  may  be  illustrated  as  follows : 

Suppose  that,  out  of  a  total  of  ten  years  which  have  been  observed,  the 
apple  crop  in  this  locality  has  been  injured  by  frost  four  years,  and  has 
been  uninjured  six  years.  If  this  data  for  ten  years  is  all  the  evidence  we 
have  bearing  on  the  probability  of  an  apple  crop,  the  best  estimate  we  can 
give  for  the  probability  that  the  apple  crop  in  this  locality  will  not  be 
injured  by  frosts  in  a  given  year  is  TV  If,  however,  our  data  extend  over 
twenty-five  years,  in  fifteen  of  which  the  apple  crop  has  been  uninjured  by 
frost,  we  again  give  ^  (£f  =  j%)  as  the  best  estimate  for  the  probability 
that  the  apple  crop  in  this  locality  will  not  be  injured  by  frosts  in  a  given 
year ;  and  certainly  more  confidence  can  be  placed  in  the  result  than  when 
only  ten  years  were  taken. 

We  might  carry  our  illustration  back  a  hundred  years  in  sixty  of  which 
the  apple  crop  in  this  locality  has  been  uninjured  by  frosts  and  we  should 
still  give  T%  as  the  most  probable  value  of  the  probability  that  an  apple 
crop  in  this  locality  will  not  be  injured  by  frost  in  a  given  year.  It  should 
be  noted  that  we  are  here  dealing  with  the  probability  of  a  probability,  or 
what  De  Morgan  has  called  the  "  presumption  of  a  probability." 

The  critical  examination  of  such  probabilities  as  the  above  derived 
from  observation  should  include  some  criterion  which  will  indicate  the 
accuracy  of  the  approximation  when  only  a  limited  number  of  cases  can  be 
examined.  Such  a  criterion  may  be  found  in  the  probable  error  of  the 
probability. 

The  problem  in  hand  may  well  be  stated  in  the  following  general  form  : 

A  bag  contains  an  indefinitely  large  number  of  white  and  black  balls  in 

unknown  ratio  ;  if  m  +  n  balls  have  been  drawn  as  a  random  sample,  and 

m  are  white  and  n  are  black,  we  give  as  the  best  value  of  the  probability 

of  drawing  a  white  ball .    What  is  the  probable  error  in  this  result  ? 

m  +  n 

Or,  in  other  words,  in  m  +  n  trials,  an  event  has  happened  m  times  and 
failed  to  happen  n  times  ;  if  we  deduce  from  this  that  — — —  is  the  probability 

that  the  event  will  happen  on  a  given  occasion,  what  is  the  probable  error 
in  this  result  ? 

From  the  works  of  Laplace,  Poisson,  and  De  Morgan,  it  follows  that 

m  0.6745      /    mn 

the  probable  error  in  is  given  by  the  formula  ±  -        —  \ 

m  +  n  m  +  n   \  m  +  n 

Applied  to  our  illustration  of  the  apple  crop  when  the  data  covered  only 
ten  years,  this  probable  error  formula  gives  ±  — •yl —  =  ±  0.104. 

From  the  magnitude  of  this  probable  error,  it  is  at  once  seen  that  the 
result  T%-  (derived  from  ten  observations)  for  the  probability  that  an  apple 
crop  will  be  uninjured  by  frost  can  at  most  be  said  to  be  but  a  crude  and 


APPENDIX 


unreliable  approximation.  It  is  more  than  an  even  wager  that  it  differs 
from  the  true  value  by  as  much  as  TV 

0.6745      12400 

When  a  hundred  years  are  used,  the  probable  error  is  —  \  — 

100      \  100 

—  0.033,  which  shows  that  the  result  T%  derived  from  a  hundred  years  is 
much  more  significant  than  that  which  was  obtained  when  only  ten  years 
were  used. 

The  following  table  will  show  how,  with  increasing  numbers,  the  probable 
error  in  the  determination  of  the  probability  decreases. 


NUMBER  OF 
OBSERVATIONS 

NUMBER  OF 
TIMES  EVENT 

PROBABILITY 
m 

PROBABLE 
ERROR 

NUMBERS  SUCH  THAT  WAGER  is 

EVEN  THAT  RANDOM  SAMPLE 
AGAIN  TAKEN   LIES  BETWEEN 

=  m  +  n 

HAPPENS  =  m 

m  +  n 

THESE  NUMBERS 

10 

6 

0.6 

±  0.104 

4.96  and          7.04 

25 

15 

0.6 

±  0.066 

13.35  an<^        !6-65 

5° 

30 

0.6 

±  0.047 

27.65  and        32.35 

100 

60 

0.6 

±  0-033 

56.7    and        63.3 

1,000 

600 

0.6 

±  0.0104 

989.6    and    1010.4 

10,000 

6000 

0.6 

±  0.0033 

9967    and    10033 

Remarks.  In  conclusion,  it  should  probably  be  said  that  we  have,  in 
the  foregoing  brief  discussion  of  statistical  methods,  touched  only  "  the 
fringe  of  a  great  subject."  We  have  for  the  sake  of  simplicity  confined 
ourselves  to  the  normal  curve  of  distribution  ;  but  it  is  to  be  hoped  that 
we  have  given  a  general  view,  in  this  short  space,  of  the  methods  by  which 
the  formulas  are  established  which  are  now  being  commonly  used  in  the 
quantitative  study  of  evolution,  and  that  the  reader  may  come  to  see  the 
proper  place  of  statistical  methods  in  solving  problems  of  this  character. 

Furthermore,  it  is  hoped  that  the  results  as  here  presented  will  be  found 
practical  in  the  sense  that  they  may  be  of  use  to  the  non-mathematical 
reader,  and  pave  the  way  for  further  investigations  along  this  line. 


INDEX 


Accessory  chromosome,  as  related  to 
sex,  634-637 ;  Gross  and  Wallace 
upon,  636;  Henking  upon,  635; 
McClung  upon,  635  ;  Paulmier  upon, 
635  ;  Wilson  upon,  634,  636. 

Acclimatization,  bearing  of,  on  insta- 
bility of  living  matter,  308-316;  by 
inoculation,  382 ;  effect  of,  upon 
transmission,  374-386 ;  extent  0^375, 
376;  in  general,  105,314-316;  of  the 
individual  and  of  the  race,  374;  of 
races,  384;  of  poplar,  376;  of  wood 
sage  on  high  and  low  altitudes,  378 ; 
permanence  of,  315;  to  chemicals, 
308-311 ;  to  cold,  313  ;  to  electricity, 
314;  to  high  temperature,  311-313; 
to  hot  springs,  379;  to  light,  313;  to 
poisons,  381-382 ;  to  temperatures, 
376-381 ;  transmission  of,  374;  with- 
out selection,  379,  381. 

Acid  secreted  by  animals  and  plants, 
267. 

Acquired  characters,  182,  308-311  ;  as 
distinct  from  congenital,  354-356;  in- 
heritance of,  349 ;  non-existence  of, 
358-360. 

Actinian,  reaction  to  chemicals,  273, 
274 ;  regeneration  in  the,  334. 

Adaptations,  350;  not  universal,  206- 
208,  412. 

Adlum,  John,  originator  of  Catawba 
grape,  134. 

Age,  influence  of,  upon  functional  activ- 
ity, 94  ;  influence  of,  upon  prepotency, 

573- 

Albinism  common  in  most  species,  114. 
Amitosis,  151. 

Amoeba,  response  to  light,  253,  254. 
Amphiaster,  147. 
Amphicyon,  50. 
Ancestral    heredity,  formula   for,  533, 

534  ;  law  of,  525-534. 
Ancestral  idioplasm,  173. 
Ancestral  units,  173. 
Animal  breeding,  654-676;  advantages 

of,  654  ;  disadvantages  of,  654,  655  ; 

disadvantage  of  many  characters  in, 

656,  657 ;  during  a  depression,  665, 


666 ;  fashion  in,  658, 659 ;  by  beginners, 
675  ;  records  in,  666-672  ;  show-ring 
consequences,  660 ;  testing  sires  and 
dams,  660-664 ;  testing  young  females, 
66 1. 

Animals,  growth  of,  influenced  by  heat, 
258,  259 ;  higher  regeneration  in, 
325,  326;  reduction  in,  compared 
with  plants,  165. 

Ant,  polymorphism  of,  20. 

Antenna  developed  as  a  foot,  43. 

Apes,  meristic  variation  in  teeth  of,  48, 

49- 

Arrays  of  the  correlation  table,  459. 

Artemia  salina,  effect  on,  by  degree  of 
salinity,  102. 

Artificial  parthenogenesis,  experiments 
in,  278-282. 

Assortative  mating,  163. 

Aster,  147. 

Asymmetry,  70. 

Atavism,  192-194. 

Attraction  of  odors,  275. 

Average  deviation,  427 ;  illustrated, 
441-443. 

Averages,  681-685 ;  arithmetic  mean, 
682,  683  ;  function  of,  682,  685  ;  geo- 
metric mean,  683,  684  ;  mode,  median, 
684,  685  ;  weighted  arithmetic  mean, 
682,  683. 

Bacillus  tuberculosis  excites  abnormal 

growth,  98. 
Bacteria,    effect    of    culture    medium 

upon,  229. 
Bailey,  experiments  in  acclimatization, 

376-378  ;  on  bud  varieties,  181 ;  on 

the  gooseberry,  130. 
Bardeleben,  studies  in  mammae,  47. 
Barrenness  to  certain  individuals,  201. 
Bathmic  influences,  202-208. 
Bear,  variation  in  digits  of,  58. 
Bees,  effect  of  food  upon,  226. 
Begonia,  regeneration  of,  238,  331. 
Belated  inheritance,  475. 
Bert,  experiments  in  grafting,  107. 
Biometrika,  journal  of  statistical  study, 

478. 


715 


7i6 


INDEX 


Biophors,  14,  208. 

Biparental  inheritance,  529-533. 

Birds,  effect  of  heat  upon  development 
of,  259 ;  variation  in  digits  of,  56. 

Birthmarks,  189-191. 

Bisexual  reproduction,  a  cause  of  varia- 
tion, 160-163;  introduces  no  new 
characters,  163. 

Blackberry,  evolution  of,  131-133. 

Blemishes  on  breeders,  590. 

Blend  in  characters,  481. 

Blended  and  exclusive  inheritance,  475. 

Bonnet,  experiments  in  regeneration, 
316. 

Bonnier,  experiments  on  acclimatiza- 
tion, 378;  experiments  with  dande- 
lion, 223. 

Born,  experiments  in  grafting,  108,  336. 

Brain  not  necessary  to  coordinated 
motion,  400,  401. 

Breeder's  business  is  the  production  of 
sires,  605. 

Breeders'  fads,  594. 

Breeders  of  speed  and  breeders  of 
breeders  contrasted,  557. 

Breeding,  polymorphism  in,  476,  477 ; 
problems  of,  outlined,  3-5 ;  purposes 
in,  599,  600 ;  systems  of,  599-627 ; 
true,  or  stability  of  type,  541-544. 

Brown-Sequard,  experiments  on  mutila- 
tions, 367. 

Bruce,  studies  in  mammae,  47. 

Bud  variation,  181. 

Bud  varieties  reproduce  by  seeds,  181. 

Bull,  E.  W.,  originator  of  Concord 
grape,  134. 

Bullfinch,  effect  of  food  upon,  228. 

Bumblebee,  antenna  of,  developed  as  a 
foot,  43. 

Burbank  system  of  planting,  643. 

Burrill,  experiments  in  crossing  straw- 
berries, 184. 

Camel,  development  of  foot  of,  60. 

Castration,  indirect  effects  of,  upon  the 
body  functions,  100. 

Catalytic  poisons,  266. 

Cats,  variation  in  digits  of,  57. 

Cattle,  acclimatization  of,  375  ;  develop- 
ment of  foot  of,  58  ;  meristic  variation 
in  digits  of,  62, 63  ;  reversions  in,  192. 

Cave  animals,  242. 

Cell,  the,  as  a  structural  unit,  143,  144; 
differentiation  in,  144  ;  effect  of  grav- 
ity upon,  239. 

Cell  division,  as  a  cause  of  variation, 
155-181;  irregularities  in,  150-152; 
mechanism  of,  145-152;  outline  of, 


146,  147;  variation  in  rate  of,  340; 
with  and  without  differentiation,  149- 
150. 

Centgener  plots,  644. 

Centrosome,  146. 

Cervical  fistulas  in  mammals,  44. 

Chance,  accounts  for  unusual  occur- 
.rences,  187;  as  distinct  from  cause, 
365 ;  law  of,  365,  366. 

Character,  defined,  17;  meaning  of 
term,  11-13. 

Characters,  acquired,  182 ;  acquired  from 
the  environment,  302-304,  308-311; 
acquired,  inheritance  of,  349 ;  are  not 
"acquired,"  358-360;  blended,  481; 
combine  in  definite  proportions,  504- 
513;  congenital  and  acquired,  354- 
356;  dependent  upon  sex,  194-196; 
development  of,  how  influenced,  361- 
363;  dominant  and  latent,  13,  14; 
dominant  and  recessive,  514,  515; 
elementary,  14;  how  behave  in  trans- 
mission, 473-478  ;  latent,  474  ;  not 
necessarily  adaptive,  412;  of  adult 
as  influenced  by  development,  350; 
of  the  individual  are  those  of  the 
race,  357;  origin  of,  413-415;  origin 
and  degeneracy  of,  contrasted,  415; 
too  many,  in  animal  breeding,  656, 
657;  variability  of,  in  same  popula- 
tion, 444. 

Chemical  action,  acclimatization  to,  308- 
311  ;  of  secretions,  383,  384. 

Chemical  effects  of  light,  240. 

Chemical  reactions  of  protoplasm,  264- 
285. 

Chemicals,  effect  of,  upon  germination, 
271  ;  rhythmical  contraction  stimu- 
lated by,  276-278. 

Chemotaxis,  271,  272. 

Chemotropism,  271-276. 

Chromatin  granules,  145. 

Chromatin  matter,  145-152. 

Chromomeres,  146. 

Chromosomes,  146-152;  but  half  the 
normal  number  of,  in  parthenogenetic 
individuals,  180;  composition  of, 
1 74 ;  constant  in  number  for  the 
species,  146;  number  of,  even  in 
bisexual  reproduction,  146;  number 
of,  reduced  by  maturation,  restored 
by  fertilization,  170;  number  of, 
sometimes  halved,  180. 

Chrysanthemums,  experiments  with,  by 
De  Vries,  119-121. 

Cleavage,  effect  of  outside  conditions 
upon,  340 ;  geometrical  character  of, 
339- 


INDEX 


717 


Coefficient,  of  assortative  mating,  532  ; 
of  correlation,  459-465 ;  short  method 
for  calculation  0^465-468;  of  heredity, 
486-488;  of  mode,  422,  423;  of  re- 
gression, 487-490 ;  of  variability,  433 ; 
of  variability,  application  of,  434 ; 
of  variability,  meaning  of,  434,  435  ; 
of  variability,  probable  error  of,  441. 

Cold,  acclimatization  to,  313  ;  effect  of, 
upon  color,  264. 

Coleoptera,  extra  eyes  in,  51. 

Color,  correlation  with  speed  in 
trotters,  468-471  ;  influenced  by  tem- 
perature, 262-264;  not  due  to  pres- 
ence of  light,  242 ;  when  important,  31. 

Combination  of  characters,  law  of,  504- 

S13- 

Combinations,  formula  for,  511 ;  of  two 
characters,  504,  505;  of  three  char- 
acters, 506,  507. 

Community  breeding,  674. 

Comparative  value  of  male  and  female, 

587- 

Conditions  of  life,  effect  of,  upon 
development,  98-105  ;  influence  of, 
upon  parthenogenesis,  102,  178. 

Congenital  and  acquired  characters, 
354-356. 

Contact,  effect  of,  upon  direction  of 
motion,  235 ;  effect  of,  upon  func- 
tional activity,  233-236. 

Continuity  in  variation,  18. 

Cope,  on  transmission,  354;  on  theory 
of  growth  force,  203,  204. 

Corn,  acclimatization  of,  375,  377,  378 ; 
effect  of  selection  upon,  445,  446; 
functional  variation  in,  83-86;  influ- 
ence of  locality  upon,  222 ;  progression 
in  oil  and  protein  content  of,  493- 
498  ;  variability  of,  427-431,  444,  447, 
448 ;  variability  of,  as  affected  by 
fertility,  449-451  ;  variation  in  com- 
position of,  83,  84. 

Correlation,  453-471,  703-708;  coeffi- 
cients of,  455-466,  705 ;  between  color, 
sex,  and  speed,  in  trotters,  468-471  ; 
between  length  and  circumference  of 
ear,  467;  weight  and  length,  461; 
definition  of,  703  ;  heredity  a  special 
case  of,  707;  meaning  of,  453~455 : 
method  of  finding  coefficient  of,  460- 
468,  707,  708 ;  shorter  formula  for 
calculation,  707,  708. 

Correlation  table,  458. 

Cows,  variation  in  functional  activity 
of,  92,  93 ;  functional  variation  in, 
77-81  ;  meristic  variation  in  mammae, 
47;  relative  fertility  of,  199. 


Crab,  segments  of,  influenced  by  para- 
site, i  oo. 
Crandall,     observations    on    curculio, 

390-393- 
Crayfish,  meristic  variation  in  oviducal 

opening,  44. 
Cross,  reciprocal,  525. 
Crossing,  608-610 ;  advantages  of,  608  ; 

disadvantages  of,  609. 
Crystals,    growth    of,    compared   with 

growth  of  living  matter,  143. 
Curculio,  egg-laying  instincts  of,  390- 

393- 
Cynips,  sting  by,  produces  functional 

deviation,  98. 
Cytoplasm,  145;  in  development,  177. 

Dallinger,  experiments  in  acclimatiza- 
tion to  heat,  379-381. 

Dams,  testing  of,  66 1. 

Dandelion,  influence  of  locality  upon, 
223. 

Darbishire,  experiments  with  mice,  524. 

Darwin,  experiments  in  cross  and  self 
fertilization,  618-624. 

Davenport  and  Castle,  experiments  on 
acclimatization,  312. 

Davenport  and  Neal,  experiments  on 
acclimatization  of  stentor,  310. 

Death  rate,  Weismann  on,  202. 

De  Candolle,  experiments  on  acclima- 
tization, 376. 

Degeneracy  contrasted  with  origin,  415, 
416. 

Degeneration  of  useful  parts,  409- 
412. 

Determinants,  152,  208,  215. 

Determination  of  sex,  629-637. 

Development,  677-680;  a  study  dis- 
tinct from  breeding,  680;  confusion 
of,  with  inheritance,  350 ;  dependent 
upon  external  conditions,  677  ;  does 
it  influence  transmission  ?  361 ;  ef- 
fect of,  upon  transmission,  372,  373, 
407-409;  from  a  half  ovum,  176; 
how  influenced,  361-363;  influence 
of  food  upon,  225-230;  influence  of 
gravity  upon,  239;  influence  of  lo- 
cality upon,  221-225;  influence  of 
moisture  upon,  230-233 ;  influence 
of  use  upon,  286-288;  influence  of, 
upon  prepotency,  574 ;  limits  of,  362  ; 
mechanism  of,  142-154;  not  an 
index  of  inherited  characters,  232; 
originates  in  geometrical  cleavage  of 
ovum,  339;  requires  good  condi- 
tions for  well-bred  individuals,  678, 
679-)  through  the  cytoplasm,  177. 


7i8 


INDEX 


Deviation,  average,  427 ;  nature  of, 
349,  350 ;  not  transmissible  as  such, 
349;  standard,  428-431;  standard, 
meaning  of,  432,  433. 

Deviation  and  probable  error  illus- 
trated, 441-443. 

De  Vries,  experiments  of,  114-129;  ex- 
perience in  plant  breeding,  642  ;  ex- 
periments with  chrysanthemum,  119- 
121;  experiments  with  primrose, 
121-129;  production  of  new  species 
by  mutation,  121-129. 

Differentiation,  by  cell  division,  149, 
1 50 ;  causes  of,  343 ;  from  internal 
causes,  144  ;  mechanism  of,  142-154; 
polarity  and  promorphology  of  ovum, 

Digitalis,  medicinal  qualities  of,  affected 

by  locality,  223. 

Digits,  meristic  variation  in,  53-64. 
Dimorphism    of    earwig,    Shorthorns, 

Herefords,  etc.,  20. 
Disappearance  of  parts,  306. 
Disappearing  parts,  288. 
Discontinuity  in  variation,  19. 
Disease,  transmission  of,  368,  384. 
Diseases  due  to  absence  of  secretions, 

269. 

Distribution,  offspring  constitute  a,  419. 
Dodd,    William,    originator    of    plum, 

I33- 
Dog,  acclimatization  of,  376;  behavior 

of,  when  deprived  of  brain,  400,  401 ; 

meristic   variation   in   teeth   of,    50 ; 

variation  in  digits  of,  57. 
Dogs,  influence  of  locality  upon,  224  ; 

telegony  in,  186. 

Dorfmeister,  experiments  with  butter- 
flies, 262. 

Double  personality,  106. 
Doubling  of  parts,  as  head,  67-69. 
Dutks,  relative  weight  of  bones  of  tame 

and  wild,  95. 

Dugong,  variation  in  digits  of,  57. 
Dwarfs,  reasons  for,  27. 
Dyads,  166. 

Earthworm,  meristic  variation  in  genera- 
tive opening  of,  44. 

Earthworms,  regeneration  in,  317-320. 

Earwig,  dimorphism  of,  20. 

Eggs,  regeneration  in,  324,  325. 

Ehrlich,  experiments  with  mice,  309. 

Eimer,  on  adaptation,  206-208  ;  on  the- 
ory of  orthogenesis,  204-208. 

Electricity,  acclimatization  to,  314. 

Embryos,  regeneration  in,  324,  325. 

Endosperm,  fertilization  of,  183,  184. 


Environment,  always  selective,  351 ; 
bearing  of,  on  instability  of  living 
matter,  290-293,  302-316;  cause  of 
evolution  of  the  horse,  302—304 ; 
direct  action  of,  307;  food,  225-230; 
general  effect  of,  upon  development, 
221-225 ;  how  influences  type  of  race, 
290-293  ;  influence  of,  upon  cleavage, 
340 ;  influence  of,  upon  partheno- 
genesis, 178  ;  influence  of,  upon  varia- 
bility, 220-293. 

Epilepsy,  transmission  of,  367. 

Evidence  that  is  not  evidence,  353. 

Evolution,  knowledge  of,  needed  in 
breeding,  5;  not  confined  to  mor- 
phology, 76;  Weismann's  theory  of, 
152. 

Ewart,  experiments  in  telegony,  186. 

Exercise,  effect  of,  upon  functional 
activity,  95,  96. 

Exophthalmia,  transmission  of,  367. 

External  influences  as  causes  of  varia- 
bility, 220-293. 

Extra  wing,  43. 

Eye,  effect  of  light  upon,  243. 

Eyes,  degeneration  of,  in  cave  species, 
411,  412  ;  supernumerary,  51. 

Fads  of  the  breeder,  594. 

Fan-top  trees,  112. 

Fashion  in  animal  breeding,  658,  659. 

Fattening,  successful  in  darkness,  246. 

Fear,  not  present  at  birth,  403. 

Female,  influence  upon,  by  previous 
mating,  185-189;  maturation  and  re- 
duction in,  165-169. 

Females,  disposal  of  surplus,  672. 

Fere,  experiments  of,  on  chicks,  259. 

Fertility,  characters  correlated  with, 
197  ;  effect  of  food  upon,  226  ;  effect 
of,  upon  type,  198,  199;  effect  of, 
upon  type  and  variability,  449-451 ; 
importance  of,  199,  584,  589;  less 
with  extremes  of  a  race  than  with  the 
means,  491 ;  often  opposed  by  selec- 
tion, 583;  relative,  196-200. 

Fertilization,  by  the  polar  body,  179, 
1 80;  connection  of,  with  mutation, 
1 80  ;  of  endosperm,  183,  184  ;  manner 
of,  161  ;  significance  of,  170 ;  influence 
of,  upon  sex,  632,  633. 

Fish,  upstream  movements,  235. 

Fisher,  studies  in  fistulas,  45. 

Flagellata,  acclimatization  to  high  tem- 
peratures, 379-381. 

Flammarion,  experiments  with  light, 
245,  246. 

Flatfishes,  415. 


INDEX 


719 


Food,  effect  of  cotton  seed  on  pork,  228; 
effect  of,  upon  bullfinches,  228  ;  effect 
of,  upon  body  temperature,  230; 
effect  of,  upon  constitutional  vigor, 
372,  373 ;  effect  of,  upon  develop- 
ment, 370-374;  effect  of,  upon  fer- 
tility, 226 ;  effect  of,  upon  functional 
activity,  96,  97  ;  energy  of,  229 ;  ex- 
cess of,  227 ;  how  reduced  by  living 
beings,  228;  influence  of,  upon  re- 
generation, 327,  328;  upon  sex,  631 ; 
upon  variability,  225-230 ;  proportion 
of,  used  in  growth,  225  ;  qualitative 
effects  of,  228-230;  quantitative  ef- 
fects of,  225-227  ;  well-bred  races  re- 
quire more,  227. 

Foundation   not   in  a  remote  female, 

595»  596- 

Fraser  on  efficiency  of  cows,  78-81. 

Fraternal  variability,  500-504. 

Free-martins,  176. 

Frequency,  curves,  686-688;  distribu- 
tion, typical,  42 1 ;  polygons,  687. 

Frequency  distribution  and  the  binomial 
theorem,  509. 

Functional  activity,  by  suggestion,  243  ; 
effects  of  light  upon,  241-246;  how 
dependent  upon  light,  251,  254. 

Functional  variation,  75-109;  between 
different  individuals  of  the  same  spe- 
cies, 77-91  ;  due  to  light,  239-254 ;  of 
same  individual  from  day  to  day,  91- 
94;  induced  by  castration,  100;  in- 
duced by  contact,  233-236;  induced 
by  external  influences,  98,  101-105; 
influenced  by  food,  96,  97,  225-230; 
influenced  by  gravity,  236-239 ;  in- 
fluenced by  hard  conditions,  97 ;  in- 
fluenced by  the  reproductive  faculties, 
100. 

Functions,  discharged  only  in  presence 
of  light,  242,  243;  exercised  under 
abnormal  conditions,  107-109. 

Funk,  Deane  N.,  car-load  lot  of  prize- 
ring  grade  cattle  belonging  to,  607. 

Furbringer,  studies  in  birds,  42. 

Galls,  98,  270. 

Gallon,  on  heredity,  478 ;  on  law  of 
ancestral  heredity,  528 ;  on  fraternal 
variability,  500,  501 ;  on  law  of  inherit- 
ance, 193,  194;  on  studies  of  stature, 
481. 

Gametic  purity,  521. 

Gemmules,  208. 

Genetic  selection,  196-200. 

Gentry,  N.  H.,  on  inbreeding,  625. 

Geotaxis,  236. 


Geotropism,  236-239  ;  in  animals,  238  ; 
of  sprout  and  root,  I II. 

Germ,  infection  of,  185 ;  influence  of 
age  or  staleness  upon,  182  ;  individu- 
ality of,  182  ;  variations  in,  are  trans- 
mitted, 348. 

Germ  plasm  and  transmission,  355. 

Germinal  selection,  162,  213-215. 

Germinal  vesicle,  166. 

Germination,  effect  of  chemicals  upon, 
271. 

Giants,  reason  for,  27. 

Glands,  specific  secretions  of,  269. 

Goltz,  experiments  on  the  dog,  400,  401. 

Gooseberry,  evolution  of,  130. 

Gorilla,  extra  incisor  in,  49. 

Grading,  602-608 ;  advantages  of,  604  ; 
abuse  of,  604 ;  begin  by,  to  get  expe- 
rience, 606;  disadvantage  of,  608; 
disappearance  of  unimproved  blood 
in,  602. 

Grafting,  frog  made  up  of  pieces  of 
two  individuals,  108;  illustrating 
stability  of  living  matter,  335,  336; 
mammary  gland  into  ear  of  guinea 
pig,  107  ;  spur  of  cock  into  comb, 
107  ;  two  species  of  animal  together, 
336 ;  two  pieces  of  tadpole,  336. 

Graphical  representation  of  statistics, 
686-690  ;  frequency  curves,  686-688; 
frequency  polygons,  687 ;  graph  of 
mathematical  function,  689,  690. 

Gravity,  effect  of,  upon  development, 
239  ;  effect  of,  upon  living  matter, 
236-239 ;  effect  of,  upon  protoplasm, 
239 ;  effect  of,  upon  regeneration, 
329-332  ;  in  struggle  with  polarity, 

237- 

Great  sires,  552  ;  the  ten  greatest,  555. 

Gross  on  the  accessory  chromosome, 
636. 

Grout,  A.  P.,  grade  Angus  steers  be- 
longing to,  605. 

Growth,  as  influenced  by  temperature, 
254-262  ;  direction  of,  due  to  light, 
249  ;  direction  of,  influenced  by  heat, 
259;  geometrical  character  of  cleav- 
age in,  339 ;  retarded  by  light,  245, 
246. 

Growth  force,  203,  204. 

Guinea  pig,  grafting  mammary  gland 
into  ear  of,  107 ;  supposed  trans- 
mission of  mutilations  of,  367. 

Habit  not  the  basis  of  instinct,  401-403. 

Habits,  are  they  transmitted?  363, 
386-403 ;  founded  on  instincts,  not 
the  reverse,  401-403  ;  learned  from 


720 


INDF.X 


elders,  353  ;  not  acquired  characters, 
358-360. 

Harris,  B.  F.,  example  of  longevity,  89. 

Heape,  experiments  on  rabbits,  190. 

Heart,  rhythmic  contraction  of,  398,  399. 

Heat,  acclimatization  to,  311-313,  379- 
381  ;  effect  of,  upon  animal  activi- 
ties, 255  ;  effect  of,  upon  direction  of 
growth,  259;  effect  of,  upon  growth 
of  animals,  258,  259;  effect  of,  upon 
growth  of  plants,  255-257. 

Hedgehog,  meristic  variation  in  verte- 
brae of,  39. 

Heliotropism,  247  ;  conditions  that  de- 
termine, 254  ;  due  to  the  luminous 
rays,  248;  general  principles  govern- 
ing, 251,  254;  of  amoeba,  253,  254; 
of  insects,  104. 

Henking  on  the  accessory  chromosome, 


35- 
rbst, 


Herst,  experments  n  regeneration, 
328. 

Herd,  management  of,  during  depres- 
sion in  prices,  665,  666  ;  records  of, 
666-670  ;  unity  of,  662  ;  without  a 
head,  664. 

Heredity,  473-547  ;  coefficient  of,  486, 
488  ;  coefficients  of  different  rela- 
tionships, 488  ;  famous  grandsires, 
556  ;  law  of  ancestral,  525-534  ;  man- 
ner of,  420-431  ;  material  basis  of, 
209;  mathematical  nature  of,  510; 
mean  of  offspring  not  mean  of  the 
parents,  490;  measure  of,  486;  mis- 
conceptions of,  473  »  offspring  differ 
from  parents,  482,  483  ;  offspring 
more  mediocre  than  the  parents, 
484-486  ;  origin  of  the  exceptional 
individual,  499,  500;  progression  in, 
492-498  ;  proper  conceptions  of,  473  ; 
special  case  of  correlation,  707  ;  statis- 
tical methods  in  study  of,  426,  478  ; 
what  is  transmitted?  511. 

Hero,  the  inbred  morning-glory,  622. 

Herringham,  studies  on  nerves,  43. 

Homoeosis,  37  ;  in  insects,  43  ;  in  verte- 
brae and  ribs,  40-42. 

Honeybee,  eyes  united,  65. 

Hopkins,  experiments  in  corn  breeding, 
83-86,  493-498. 

Horns,  meristic  variation  in,  52,  53,  66  ; 
regeneration  of,  326. 

Horse,  begging  instinct  in,  353  ;  causes 
of  evolution  of,  302-304;  defective 
voice  in,  353  ;  development  of  foot 
of,  58,  59  ;  evolution  of,  298-305  ; 
extreme  age  of,  89;  meristic  varia- 
tion in  digits  of,  60,  61. 


Horses,  acclimatization  of,  375  ;  corre- 
lation between  color,  sex,  and  speed, 
468-471;  inbreeding  in,  624;  power 
of  transmission  among,  408 ;  telegony 
in,  185. 

Horseshoe  kidney,  65. 

Hot  springs,  Infusoria  in,  311;  life  in, 

379- 

Houghton,  Abel,  originator  of  goose- 
berry, 130. 

Hunter,  experiments  in  grafting,  107. 

Huntington,  Randolph,  on  breeding, 
624. 

Hybrids,  character  of  descendants  of, 
514-521;  Mendel's  law  of,  513-525; 
sterility  of,  607. 

Hypertrophy,  288,  289. 

Idants,  173. 

Ideals  in  selection,  578,  579. 

Idioplasm,  1 52,  208. 

Ids,  146,  208' 

Illinois  station,  system  of  planting  at,646. 

Immunity,  natural  and  acquired,  382. 

Improvement,  upper  limits  of,  582. 

Inbreeding,  613-626;  advantages  of, 
614,  615;  A.  J.  Lovejoy  on,  625; 
among  animals,  624-626;  Darwin's 
experiments  on,  618-624  ;  disadvan- 
tages of,  615;  forms  of,  613,  614; 
how  to  practice,  626;  often  more 
vigorous  than  outbreeding,  622-624 ; 
lack  of  vigor  and  low  fertility  com- 
mon defects,  616,  617  ;  N.  H.  Gentry 
on,  625 ;  not  all  inbred  individuals 
inferior,  620-623 ;  not  necessarily  dis- 
astrous, 616-626;  Randolph  Hunt- 
ington on,  624;  special  dangers  in, 
616;  total  effects  of,  619,  620. 

Individual,  the,  352;  possesses  all  the 
characters  of  the  race,  357,  360. 

Individuality  in  offspring  from  same 
parents,  503. 

Infertility,  a  common  defect,  616,  617  ; 
effect  of,  584,  589. 

Inheritance,  complex,  527;  belated, 
475;  blended  and  exclusive,  475; 
from  separate  ancestors,  527  ;  from 
the  race,  193,  194;  not  limited  to  sex, 
474  ;  of  acquired  characters,  292,  349; 
offspring  more  mediocre  than  the 
parents,  484-486;  particulate,  476; 
progression  in,  492-498. 

Inoculation,  immunity  by,  382. 

Insect  poisons,  270. 

Instability,  of  living  matter,  illustrated 
by  origin  of  differentiated  tissue,  336- 
338  ;  of  protoplasm,  398. 


INDEX 


721 


Instinct,  104-106;  is  it  founded  on 
habit  ?  388-390 ;  not  founded  on 
habit,  401-403  ;  not  unerring,  389. 

Instinctive  acts,  a  series  of  reflexes, 
398-401 ;  not  uniformly  performed, 
390-394. 

Instincts,  are  they  inherited  habits  ? 
386-403 ;  due  to  external  stimuli, 
252 ;  intelligence  not  necessary  to, 
397,  398 ;  nature  of,  387,  388 ;  origi- 
nate in  reflex  action,  394-397  ;  not 
always  adaptive,  394. 

Intelligence  not  necessary  to  compli- 
cated acts,  397,  398. 

Internal  influences  affecting  the  race, 
196-217. 

Intra-uterine  influences,  189-191. 

Jochemke,  variation  in  functional  ac- 
tivity of,  92,  93. 

Kangaroo,  development  of  foot  of,  60. 
Kanthack,     experiments     with     snake 

poison,  309. 
Kerrick,  L.  H.,  car-load  lot  of  graded 

steers,  603 ;    on    herd    records,    668, 

669. 

Lamarckians,  opposers  of,  413;  views 
of,  413. 

Lancaster,  Ray,  defines  thremmatol- 
ogy* i- 

Latent  characters,  474. 

Law  of  ancestral  heredity,    194,    525- 

534- 

Law  of  chance,  365,  366. 

Life,  material  basis  of,  213. 

Light,  acclimatization  to,  313  ;  chemical 
effects  of,  240 ;  effects  of,  upon  fixa- 
tion of  carbon,  239 ;  effect  of,  upon 
functional  activity,  241-246;  effect 
of,  upon  living  matter,  239-254  ;  effect 
of,  upon  regeneration,  328 ;  general 
effects  of,  251,  254;  influence  of, 
upon  direction  of  growth,  247  ;  influ- 
ence of,  upon  eyes  of  dead  sharks, 
395;  influence  of,  upon  locomotion, 
247  ;  not  necessary  to  development 
of  color,  242  ;  rigor,  244  ;  specific  rays 
of,  that  exert  effect  upon  growth,  245, 
246 ;  vital  limits  as  to,  244. 

Line  breeding,  610-613  ;  advantages  of, 
61 1;  the  best  system  for  improvement, 
612;  disadvantages  of,  61 1,  612. 

Living  matter,  distinguished  from  non- 
living, 142,  143;  influence  of  light 
upon,  239-254;  parallelism  with 
non-living  matter,  210,  211;  relative 


stability  and  instability  of,  295-346; 
response  to  gravity,  236-239. 

Locality  a  comprehensive  term,  224. 

Locomotion,  direction  of,  due  to  light, 
250. 

Loeb,  experiments  in  chemotropism, 
273-276;  experiments  in  heliotro- 
pism,  250-254;  experiments  in  par- 
thenogenesis, 278-282  ;  experiments 
in  rhythmic  contraction,  276-278; 
observations  upon  Infusoria,  308. 

Longevity,  201,  202;  earlier  offspring 
live  longest,  502. 

Lothelier,  moisture  experiments,  231. 

Lovejoy,  A.  J.,  line-bred  swine  belong- 
ing to,  6n,  612;  on  herd  records, 
670 ;  on  inbreeding,  625. 

Lubbock,  experiments  with  ants,  273. 

McClung  on  the  accessory  chromosome, 

635- 

Male,  maturation  and  reduction  in,  169, 
170. 

Male  and  female,  comparative  value  of, 
587. 

Mammae,  meristic  variation  in,  46,  47. 

Mammary  tissue,  grafted  on  ear  of 
guinea  pig,  107  ;  in  various  parts  of 
the  body,  46. 

Man,  auricular  appendages  on,  45 ; 
cervical  fistulae  in  meristic  variation 
in  digits  of,  54,  55,  69;  meristic  vari- 
ation in  mammae  of,  47 ;  meristic 
variation  in  ribs  of,  40,  41 ;  milk  se- 
cretion not  confined  to  females,  107 ; 
telegony  in,  188. 

Manatee,  variation  in  digits  of,  54. 

Marks  due  to  prenatal  influences,  189- 
191. 

Material  basis  of  life,  213. 

Maturation  and  reduction,  a  cause  of 
variation,  163-181  ;  in  animals  and 
plants  compared,  165;  in  male  and 
female  compared,  164. 

Maturation  in  the  female,  165-169. 

Mean,  calculation  of,  424 ;  of  offspring 
not  the  mean  of  the  parentage,  490 ; 
practical  use  of,  425 ;  probable  error 
of,  440. 

Measurements,  hints  on  taking  of,  435  ; 
scheme  of,  436. 

Meat  production,  variation  in,  81,  82. 

Mechanism  of  development  and  differ- 
entiation, 142-154. 

Melon,  influence  of  locality  upon,  221. 

Men,  milk  secretion  by,  107. 

Mendel,  Gregor  Johann,  513. 

Mendel's  experiments,  516-521. 


722 


INDEX 


Mendel's  law,  513-525;  experimental 
evidence  on,  516-521  ;  experiments 
with  mice,  524. 

Mendel's  law  and  gametic  purity,  521. 

Merinos  in  New  Zealand,  223. 

Merism,  33. 

Meristic  variation,  33-74 ;  cervical  fis- 
tulae  and  auricular  appendages,  44- 
46;  doubling  of  complicated  parts, 
64-69;  due  to  cell  division,  72,  158; 
homoeosis  in,  37  ;  in  digits,  53-64 ; 
in  eyes,  51;  in  generative  parts,  44; 
in  head,  67,  68;  in  horns,  52,  53;  in 
legs,  64 ;  in  mammae,  46,  47 ;  in  radial 
series,  70-73 ;  in  spinal  nerves,  42 ; 
in  teeth,  48-51 ;  in  vertebrae  and  ribs, 
39-42;  in  wings,  51. 

Mice,  acclimatization  of,  to  ricin,  309 ; 
variation  in  digits  of,  58. 

Microsomes,  146. 

Mid-parent,  Gallon's,  481  ;    Pearson's, 

529- 

Mid-parent  deviation,  formula  for,  531. 

Mid-parent  variability,  formula  for,  531. 

Milk  production,  variation  in,  78-80, 
92,  93  ;  transmitted  by  males,  360. 

Milk  secretion  by  males,  105,  107. 

Minnesota  station,  system  of  planting 
at,  644. 

Mitosis,  as  a  cause  of  variation,  155- 
181  ;  details  of,  145-152;  irregular- 
ities in,  150-152;  pathological,  150, 

IS1-' 

Mixed  breeding,  purity  in,  507. 
Modal  coefficient,  422,  423. 
Mode,   the,    421,    422;    empirical   and 
theoretical,  422  ;  practical  value  of, 

423- 

Modifications  due  to  external  influences, 
transmission  of,  348-417. 

Moisture,  effect  of,  upon  development, 
230-233;  effect  of,  upon  spiny 
growth,  231. 

Monte  Carlo  and  roulette,  365. 

Morgan,  observations  on  acclimatiza- 
tion to  heat,  311  ;  on  fear  in  chicks, 

403- 

Morgan  horse,  296. 
Morning-glory,    Darwin's    experiments 

in  inbreeding,  621-624. 
Morphological  variation,  25-29  ;  causes 

of,  27  ;  in  mulberry  leaves,  26. 
Moss  roses,  a  bud  variety,  181. 
Moths,  flight  of,  determinedby  light, 250. 
Movement  induced  by  contact,  234. 
Mulberry  leaves,  polymorphism  in,  26. 
Multiplying  plots,  650. 
Multipolar  mitosis,  151. 


Mumford,  experiments  in  feeding,  82  ; 
on  pork  production,  228. 

Muscle  fiber,  effect  of  light  upon,  247. 

Mutability  of  species,  298-305. 

Mutants,  21;  origin  of,  in  toadflax, 
115-118. 

Mutation,  biological  significance  of,  1 36, 
137;  distinguished  from  ordinary  va- 
riation, no;  economic  significance 
of,  135,  136;  in  chrysanthemum,  1 19- 
121  ;  in  primrose,  121-129;  ^aws  °f> 
127-129;  in  toadflax,  115-118;  in 
American  native  fruits,  129-135;  in 
general,  110-138;  relation  of,  to  re- 
duction and  fertilization,  180. 

Mutation  and  elementary  species,  128. 

Mutation  and  parthenogenesis,  179. 

Mutilations,  are  they  transmitted  ?  363- 
368 ;  experiments  upon  transmission 
of,  367  ;  resemblance  of,  to  natural 
deformity,  366. 

Nageli,  experiments  with  copper,  268. 
Narwhal,  meristic  variation  in  tusk  of, 

70. 

Natural  selection  always  at  work,  588. 
Nectarine,  mutant  of  the  peach,  112. 
Neo-Darwinians,  354. 
Neo-Lamarckians,  354. 
Nerves,  meristic  variation  in,  42. 
Neugebauer,  studies  in  mammas,  47. 
Nucleus,  145-152. 

Odors,  attraction  of,  275. 

Oil  content  of  corn,  83-85  ;  effect  of 
selection  upon,  445,  446 ;  progression 
in  breeding  for,  496-498. 

Old  Granny,  example  of  longevity  and 
extreme  fertility,  89,  90. 

Oocyte,  165. 

Oogonia,  165. 

Orientation,  247. 

Origin  of  characters,  413-415. 

Orthogenesis,  204-208 ;  explained  by 
germinal  selection,  215. 

Osborn,  researches  on  evolution  of  the 
horse,  302. 

Ossification,  99. 

Otocyon,  teeth  of,  50. 

Overfeeding,  evil  effects  of,  227. 

Ovum,  r.6 1,  165;  polarity  of,  341-343; 
promorphology  of,  341  ;  segmenta- 
tion of,  without  fertilization,  177- 
180. 

Oxygen,  effect  of,  upon  protoplasm,  265. 

Panmixia,  288. 

Parry,  originator  of  blackberry,  132. 


INDEX 


723 


Parthenogenesis,  162 ;  but  one  polar 
body  in,  179;  influenced  by  condi- 
tions of  life,  178  ;  influenced  by  tem- 
perature, 281 ;  Loeb's  experiments  in, 
278-282 ;  but  half  the  normal  num- 
ber of  chromosomes  in,  180. 

Parthenogenesis  and  mutation,  179. 

Parthenogenetic  reproduction,  variation 
in,  177-180. 

Particulate  inheritance,  476. 

Paulmier  on  the  accessory  chromosome, 

635- 

Pearson,  on  bathmic  influences,  203 ; 
on  causes  of  variability,  220;  on  fer- 
tility, 196-198  ;  on  law  of  ancestral 
heredity,  529 ;  on  reduction  of  varia- 
bility, 536;  on  telegony,  188. 

Pedigree,  importance  of,  592 ;  records 
of,  670-672. 

Pedigrees,  fashionable,  595. 

Peloric  flowers  in  toadflax,  115-118. 

Performance,  as  a  guide  to  breeding 
powers,  558-567 ;  records  in  plant 
breeding,  650. 

Pfeffer,  experiments  on  chemotropism, 

273- 

Photosynthesis,  240. 

Phototaxis,  248. 

Phototonus,  248. 

Physiological  selection,  201,  589. 

Physiological  units,  14,  17,  152,  208- 
213  ;  as  affected  by  reduction,  170. 

Pigs,  acclimatization  of,  375;  develop- 
ment of,  58 ;  meristic  variation  in 
digits  of,  63. 

Planarian,  regeneration  of,  321,  322, 
334,  335 ;  regeneration  of  starving, 
327  ;  regeneration  of,  when  split,  335. 

Plant  breeding,  639-651;  advantages 
and  limitations  of,  639-641  ;  plot  or 
row  system  for,  644-649 ;  soil  and 
culture  conditions  for,  641-643;  sys- 
tems of  planting  in,  643—649. 

Plant  lice,  effect  of  conditions  upon 
reproduction,  102;  parthenogenetic 
only  at  high  temperatures,  281. 

Plants,  effect  of  heat  upon  growth  of, 
255-257  ;  regeneration  in,  325. 

Plot  system  of  planting  in  breeding 
work,  644-646. 

Plums,  evolution  of,  133. 

Poison  ivy,  immunity  to,  308. 

Poisons,  acclimatization  to,  308-311, 
381,  382;  catalytic,  266,  267;  from 
insects,  270 ;  toxic,  268. 

Polar  bodies,  164;  formation  of,  167;  for- 
mation of,  illustrated,!  68  ;  fertilization 
by,  179, 1 80;  formation  of  second,  167. 


Polarity,  in  struggle  with  gravity,  237 ; 
of  ovum,  341-343. 

Pollination,  indirect  effect  of,  185. 

Polymorphism  in  practical  breeding, 
476,  477  ;  with  regard  to  sex,  20. 

Pork,  effect  of  cotton  seed  upon, 
228. 

Precipitin  test,  382. 

Preferential  mating,  163. 

Prenatal  influences,  189-191. 

Prepotency,  551,  575;  as  affected  by 
age»  573 »  as  indicated  by  perform- 
ance, 558-567  ;  as  related  to  consti- 
tutional vigor,  573 ;  as  shown  by 
trotting  records,  551-566;  influence 
of  development  upon,  574 ;  because 
of  sex,  567-570. 

Primrose,  seven  mutants  in  eight  gen- 
erations of,  127. 

Probability,  692-698 ;  combination  of, 
693,  694  ;  definition  of,  693  ;  place  of, 
in  science  generally,  692,  693. 

Probability  curves,  695-701 ;  normal 
curve,  696,  699,  701. 

Probable  error,  437-440,  698-703;  of 
coefficient  of  correlation,  459-468, 
703,  711 ;  of  coefficient  of  variability, 
441.703,710;  of  coefficient  of  regres- 
sion, 466,  703  ;  of  mean,  440,  701,  703; 
of  single  variate,  698,  703 ;  of  stand- 
ard deviation,  440,  702,  703. 

Probable  error  and  deviation  illustrated, 

441-443- 

Probable  error  in  estimate  of  probabil- 
ity, 709-713. 

Progression,  a  few  offspring  extreme, 
492-498 ;  in  oil  content,  496-498  ;  in 
protein  content,  493-495 ;  origin  of 
the  exceptional  individual,  499,  500. 

Protein  content  of  corn,  83-85 ;  effect 
of  selection  upon,  445,  446;  progres- 
sion in  breeding  for,  494,  495. 

Protoplasm,  a  chemical  substance  with 
chemical  properties,  144;  activity  of, 
due  to  external  as  well  as  to  inter- 
nal impulses,  398-401 ;  as  influenced 
by  chemical  agents,  264-285  ;  effect 
of  contact  upon,  233-236;  effect  of 
gravity  upon,  239 ;  effect  of  heat  and 
cold  upon,  255;  irritability  of,  398; 
effect  of  external  agents  upon,  396, 
397;  physical  basis  of  life,  142,  143; 
relative  stability  and  mutability  of, 

295'  346. 
Protozoa,  but  one  maturation  division 

in,  165. 
Python,  meristic  variation  in  vertebrae 

and  ribs  of,  39,  40. 


724 


INDEX 


Qualitative  effects  of  food,  228-230. 
Quantitative  effects  of  food,  225-228. 

Race,  affected  by  internal  influences, 
196-217  ;  extinction  of,  415. 

Radial  symmetry,  34. 

Random  sample,  420,  708,  709. 

Rat,  tail  of,  grafted  into  back,  107. 

Rational  selection,  592,  593. 

Rats,  variation  in  digits  of,  58. 

Reaumur,  experiments  in  regeneration, 
316. 

Reciprocal  cross,  525,  6 to. 

Records,  in  animal  breeding,  666-672  ; 
in  plant  breeding,  645-649;  of  the 
herd,  666-670;  of  pedigree,  670-672. 

Redfield,  Casper  L.,on  prepotency,  574  ; 
on  transmission,  407,  408. 

Reduction,  a  cause  of  variability,  163- 
181,  175,  176;  apparent  purpose  of, 
167;  connection  with  mutation,  180; 
end  products  of,  167,  168;  how  ac- 
complished, 169;  illustrated,  168;  in 
the  male,  169,  170;  in  the  female, 
165-169;  in  male  and  female  com- 
pared, 164;  in  plants,  171-173;  in 
animals  and  plants  compared,  165; 
losses  sustained  by,  170;  opportuni- 
ties for  accident  during,  171  ;  Weis- 
mann's  prediction  concerning,  173, 
174;  results  in  loss  of  chromatin 
matter,  170,  173;  significance  of,  170. 

Reflex  action  the  basis  of  instinctive 
acts,  394-397- 

Regeneration,  bearing  of,  on  stability 
of  living  matter,  316-332;  by  trans- 
formation, 323  ;  character  of  restored 
part  in,  326,  327  ;  effect  of  age  upon, 
331  ;  effect  of  flowering  period  upon, 
331  ;  effect  of  food  upon,  327,  328; 
effect  of  gravity  upon,  329-332 ; 
effect  of  light  upon,  328 ;  effect  of 
temperature  upon,  327  ;  first  in  form, 
afterward  in  size,  317;  growth  in, 
not  uniform,  317,  318;  from  oblique 
surface,  334 ;  heteromorphosis  in, 
332;  internal  factors  in,  332-335;  in 
animals,  316;  in  earthworms,  317- 
320 ;  in  embryos  and  eggs,  324,  325  ; 
in  fish,  318;  in  higher  animals,  325, 
326;  in  the  planarian,  321,  322,  334, 
335;  in  plants,  325;  in  salamander, 
316;  in  actinian,334;  lateral,  333,  335  ; 
not  always  complete,  318-320,323,325; 
polarity  in,  320,  329-333  ;  what  deter- 
mines character  of  restored  part,  333. 

Regression,  advantage  and  disadvan- 
tage of,  485  ;  as  to  stature,  479-481  ; 


diagram  of,  489 ;  offspring  more  me- 
diocre than  parents,  484-486. 

Regression  coefficient,  466,  487-490. 

Regression  table,  479-482. 

Reversion,  16,  192-194. 

Reversion  and  atavism,  305. 

Rheotaxis,  235. 

Rhinoceros,  development  of  foot  of,  60. 

Ribbert,  grafting  mammary  gland  on  ear 
of  guinea  pig,  336. 

Roebuck,  meristic  variation  in  horns 
of,  53,  65,  66. 

Romanes,  on  instinct,  389;  on  trans- 
mission, 354 ;  on  transmission  of 
mutilations,  367. 

Roots,  development  of,  by  external 
conditions,  104;  growth  of,  in  run- 
ning water,  235. 

Rose,  record  of,  with  Nora,  78-80. 

Roulette  wheel,  how  made  up,  365. 

Roux,  experiments  upon  segmenting 
frogs'  eggs,  343  ;  on  preparation  of 
antitoxin,  310. 

Row  system  of  planting  in  breeding 
work,  646-649. 

Sachs,  experiments  on  growth  of  plants, 
256. 

Salamander,  regeneration  in,  316. 

Saline  solutions,  effect  of,  upon  devel- 
opment, 282-285. 

Sample,  random,  420. 

Sawfly,  antenna  of,  developed  into  a 
foot,  43. 

Schmankewitsch,  experiments  with  Ar- 
temia,  102,  283. 

Sea  urchin,  Loeb's  experiments  with, 
278-282. 

Seal,  variation  in  digits  of,  57. 

Secretions,  chemical  action  of,  383,  384. 

Seed  production  a  business,  650. 

Seedlings,  response  of,  to  gravity,  236. 

Seeds,  effect  of  moisture  upon,  232. 

Segmentation,  dependence  of,  upon 
water  content,  178;  geometrical 
character  of  cleavage  in,  339 ;  not 
dependent  on  fertilization,  178. 

Selection,  577-598 ;  blemishes  and 
accidental  injuries  bearing  on,  590; 
cessation  of,  288  ;  effect  of,  upon  type 
and  variability,  445,  446;  general 
principles  involved  in,  581-592  ;  his- 
torical knowledge  of  the  breed  essen- 
tial in,  579,  581  ;  ideals  in,  578,  579; 
importance  of  pedigree  in,  592  ;  in- 
creased number  of  "  points  "  in,  590  ; 
indirect  effects  of,  447,  448  ;  influence 
of  age  in,  589 ;  fallacy  of  "  foundation  " 


INDEX 


725 


females  in,  595,  596 ;  limit  of  power 
of,  to  reduce  variability,  534-537  ; 
natural  selection  always  at  work, 
588  ;  need  of  large  numbers  for,  584  ; 
need  of  the  actual  test  for,  586 ; 
objects  of,  579 ;  often  against  vigor 
and  fertility,  583  ;  physiological,  589  ; 
power  of,  to  modify  type,  291,  537- 
544;  progressive,  197;  purpose  of, 
581;  rational,  592,  593;  reduces  to 
utility  basis,  591  ;  results  in  absolute 
increase  of  quality,  582 ;  reversal  of, 
288;  size  in  dam,  quality  in  sire,  588  ; 
the  exceptional  breeder  not  always 
the  exceptional  individual,  585  ;  upper 
limits  of  improvement,  583  ;  value  of 
the  exceptional  breeder,  585  ;  visible 
characters  deceptive  in,  508,  510. 

Selective  death  rate,  201,  202. 

Selective  influence  of  environment,  35 1 . 

Sewall,  experiments  with  snake  poison, 

3°9- 

Sex,  correlation  with  speed  in  trotters, 
468-470  ;  determination  of,  629-637  ; 
differences  slight,  630  ;  in  mammals, 
634  ;  in  bees,  632  ;  in  plant  lice,  632  ; 
in  wasps,  633 ;  influence  of,  upon 
development  of  characters,  194-196; 
influence  of  fertilization  upon,  632, 
633;  influence  of  nutrition  upon,  631; 
inheritance  not  limited  to,  474 ;  re- 
lated to  the  accessory  chromosome, 

634-637- . 
Sex  determination,  theories  upon,  629, 

630. 
Sexes,  comparative  variability  of,  570, 

573;  equipotent,  568. 
Sharks,  effect  of  light  on  eyes  of  dead, 

395- 

Sheep,  development  of  foot  of,  58  ;  me- 
ristic  variation  in  digits  of,  63. 

Shorthorns,  polymorphism  in,  20. 

Show-ring  consequences,  660. 

Shy  breeders,  119,  200. 

Sire,  quality  in,  588. 

Sire  more  than  half  the  herd,  587. 

Sires,  great,  552;  market  for,  673;  of 
sires  and  sires  of  dams  contrasted, 
553-555  :  testing  of,  662-664. 

Smoothing  of  figures,  690,  691. 

Snakes,  rudimentary  legs  of,  58. 

Spallanzani,  experiments  in  regenera- 
tion, 316. 

Species,  supposed  conversion  of,  283. 

Sperm  cell,  161. 

Spermatocytes,  169. 

Spermatozoon,  161  ;  function  of,  281. 

Spinal  nerves,  meristic  variation  in,  42. 


Spireme,  146. 

Sports,  21,  in. 

Stability,  of  type,  296,  297 ;  shown 
by  reversion,  305 ;  of  living  matter 
illustrated  by  grafting,  335,  336 ;  by 
regeneration,  316-335. 

Stability  and  instability  of  living  matter, 
295-346  ;  illustrated  by  development 
and  differentiation,  338. 

Standard  deviation,  42^-431,  698-703, 
as  a  measure  of  variability,  700 ;  con- 
trasted with  average  deviation,  431  ; 
illustrated,  441-443 ;  meaning  of, 
432,  433  ;  probable  error  of,  440,  702, 
703  ;  shortened  method  of,  429. 

Standards    should    not    be    changed, 

579- 

Starvation,  effects  of,  upon  regenera- 
tion, 327. 

Statistical  methods,  426,  681-713  ;  need 
of,  in  heredity  studies,  478,  68 1  ; 
reliability  of,  692. 

Stature,  transmission  0^480-484,  488- 

493'  499-502- 

Steers,  functional  variation  in,  82. 

Stentor,  acclimatization  of,  to  HgCl2, 
310;  regeneration  in,  323. 

Stereotropism,  250. 

Sterility  of  hybrids,  609. 

Sterling,  originator  of  blackberry,  133. 

Stirp,  14,  152,  208. 

Strasburger,  growth  below  zero,  313. 

Strawberry,  evolution  of,  131. 

Struthers.  observations  on  ribs,  40. 

Stunted  animals,  225. 

Substantive  variation,  30-32 ;  impor- 
tance of,  31. 

Suprarenal  glands,  383. 

Swine,  development  of  foot  of,  58; 
inbreeding  in,  625. 

Symmetry,  34-37  ;  bilateral,  34,  65-68 ; 
dorsal  and  ventral,  as  distinct  from 
right  and  left,  34-36 ;  in  variable  parts, 
68-70 ;  longitudinal,  36 ;  radial,  34. 

Syndactylism,  63,  66. 

Systems  of  breeding,  599-627. 

Tapir,  development  of  foot  of,  60. 

Teeth,  meristic  variation  in,  48-51. 

Telegony,  185-189;  in  dogs,  186 ;  in 
horses,  185;  in  man,  188;  proof  by 
method  of  instance,  187  ;  scientific 
objections  to,  188. 

Teleology,  principle  not  universal,  207. 

Temperature,  acclimatization  to,  311- 
313,376-381;  all-pervading, 264;  effect 
of,  upon  color,  262-264;  upon  growth, 
254-262;  upon  parthenogenesis,  281; 


726 


INDEX 


upon  regeneration,  327  ;  of  the  body, 
230. 

Ten  great  sires,  555. 

Teratology,  100. 

Testing  sires  and  dams,  660-664. 

Testing  young  females,  66 1. 

Tetrads,  166. 

Thigmotaxis,  235. 

Thremmatology,  compared  with  evolu- 
tion, 2  ;  defined,  I  ;  more  than  a  study 
in  morphology,  8;  problems  of,  out- 
lined, 3-5. 

Thyroid,  effect  of  extirpation  of,  383. 

Toadflax,  experiments  with,  by  De  Vries, 
115-118. 

Toxic  poisons,  268. 

Transmission,  347—417  ;  heterogeneous, 
426;  how  characters  behave  in,  473— 
478;  manner  of,  420-431;  effect  of 
acclimatization  upon,  374-380  ;  effect 
of  development  upon,  407-409 ;  of 
disease,  368,  384  ;  of  effects  of  food, 
370-374;  of  effects  of  use  and  dis- 
use, 404-407  ;  of  habits,  386-403  ;  of 
immunity,  3^2;  of  mutilations,  364- 
368 ;  of  stature,  480 ;  of  variation, 
348-417  ;  not  unless  germ  is  affected, 
416,  417;  offspring  not  like  parents, 
482,  483 ;  offspring  more  mediocre 
than  the  parents,  484-486 ;  origin  of 
the  exceptional  individual,  499,  500 ; 
progression  in,  492-498 ;  what  is 
transmitted,  511. 

Trembley,  experiments  on  regeneration, 
3,6. 

Trotters,  correlation  between  color, 
sex,  and  speed,  468-471. 

Trotting  records  showing  prepotency, 

SSJ-S66- 

Tumors,  99,  271. 

Turtle,  double  head  of,  67. 

Twins,  176;  identical,  176;  from  a  sin- 
gle ovum,  176. 

Type,  as  distinct  from  the  individual, 
352;  conceptions  of,  420-425;  effect 
of  environment  upon,  290-293 ;  ef- 
fect of  fertility  upon,  198,  199,  449- 
451 ;  effect  of  selection  upon,  445, 
446 ;  mutability  of,  298-305  ;  natural, 
422 ;  power  of  selection  to  modify, 
537-544 ;  selection  standard  for,  420, 
425;  stability  of,  296,  297,  541,  544. 

Type  and  variability,  419-451. 

Use  a  function  of  structure,  387. 
Use  and  disuse,  effect  of,  285-290;  ef- 
fect of,  upon -functional  activity,  95, 


96;  effects  of,  when  transmitted,  404- 
407  ;  influence  on  transmission,  363. 

Variability,  among  offspring  of  same 
parents,  500-504 ;  as  affected  by  fer- 
tility, 449-451 ;  coefficient  of,  433 ;  de- 
termined from  groups,  426  ;  deviation 
from  type,  425;  effect  of  selection 
upon,  445,  446 ;  erroneous  concep- 
tions of,  425,  426;  highest  in  fertile 
soils,  642 ;  in  heights  of  brothers, 
501;  in  oil  and  protein,  445,  446; 
in  physical  characters  of  corn,  447, 
'  448 ;  limitations  of,  8,  9  ;  limit  to  the 
reduction  of,  534-537 ;  measure  of, 
by  average  deviation,  427 ;  measure 
*of,  by  standard  deviation,  428-431  ; 
nature  of,  10,  n  ;  of  different  char- 
acters in  same  population,  444 ;  of 
sexes,  570-573;  ultimate  unit  of, 
15-17;  units  of,  208-213. 

Variation,  bud,  181  ;  causes  of,  141- 
347 ;  caused  by  bisexual  reproduc- 
tion, 160-163  ;  caused  by  cell  division, 
155-181  ;  caused  by  external  influ- 
ences, 220-293;  caused  by  reduc- 
tion process,  163-181,  causes  of, 
must  be  studied,  141  ;  confined  to 
racial  characters,  358 ;  continuous 
and  discontinuous,  18-22;  correlated, 
16;  does  not  extend  to  non-living 
matter,  23 ;  due  to  age  or  staleness 
of  germ,  182;  due  to  temperature, 
262-264;  functional,  75-109;  func- 
tional, due  to  age,  94 ;  functional, 
between  different  individuals  of  the 
same  species,  77-91 ;  functional,  due 
to  use  or  disuse,  95,  96 ;  functional, 
from  day  to  day,  same  individual, 
91-94;  functional,  induced  by  ex- 
ternal influences,  98,  101-105;  func- 
tional, influenced  by  feed,  96,  97 ; 
how  far  possible,  29=5-346;  induced 
by  food,  225-230;  influence  of  mois- 
ture upon,  230-233;  influenced  by 
fertility,  196-200;  influenced  by  the 
reproductive  functions,  100;  influ- 
enced by  slight  chemical  changes, 
210,  2ii  ;  in  chemical  composition  of 
seeds,  —  corn,  8^-86  ;  in  fertility,  90  ; 
in  general  body  faculties,  86;  in  meat 
production,  81—83  >  i'1  m^k  secretion, 
77-8 1,  91-93;  in  parthenogenetic  re- 
production, 177-180;  in  sugar  produc- 
tion, 86;  in  race,  caused  by  external 
influences,  290-293  ;  in  rate  of  cell 
division,  340 ;  in  vital  functions, 


INDEX 


727 


87-89;  internal  causes  of,  155-217; 
kinds  of,  17-23;  morphological,  sub- 
stantive, meristic,  functional,  22 ; 
meristic,  33-74 ;  morphological,  25- 
29;  substantive,  30-32;  quantitative 
and  qualitative,  17;  nature  of,  356- 
364 ;  not  notably  less  in  partheno- 
genesis, 178;  through  inheritance  of 
modifications,  292  ;  units  of,  208-213; 
universality  of,  7,  8. 

Variations,  due  to  causes  internal  to  the 
germ,  are  transmitted,  348 ;  due  to 
external  influences,  transmission  of, 
348-417  ;  due  to  causes  not  affecting 
the  germ  not  transmitted,  416,  417; 
occur  according  to  the  binomial  the- 
orem, 508,  509. 

Varieties,  duration  of,  544,  545. 

Vigor,    often     opposed    by    selection, 

583- 

Vital  limits  as  to  light,  244. 
Vochting's  experiments  on  gravity  and 

polarity,  237. 

Wallace  on  the  accessory  chromosome, 

636. 

Water,  effect  of,  upon  growth,  230-233. 
Wattles,  46. 

Wayland,  originator  of  plum,  133. 
Weeping  varieties,  112. 


Weismann,  experiments  with  butter- 
flies, 262-264  5  on  death  point,  202  ; 
on  germinal  selection,  214  ;  on  origin 
of  characters,  413,  414;  prediction 
concerning  loss  of  hereditary  matter, 
173,  174;  on  transmission,  354. 

Whale,  variation  in  digits  of,  57. 

Wheat,  acclimatization  of,  376;  influ- 
ence of  locality  upon,  222. 

White,  Hugh,  originator  of  Clinton 
grape,  134. 

Whitney,  fund  for  exploration,  302. 

Willow,  effect  of  gravity  on  growth  of, 
238. 

Wilson,  John,  originator  of  blackberry, 
132. 

Wilson  on  the  chromosome,  634. 

Wing,  supernumerary,  4 },  51. 

Writing  with  the  feet,  286,  287. 

Xenia,  183,  184. 

Young  breeders,  675. 

Yucca  moth,   105;  instinctive  acts  of, 

388. 
Yule's  formula,  456,  457. 

Zoja,  experiments  in  regeneration  of 
blastomeres,  325. 


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